HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) All Versions of this Article: 294/2/G391    most recent 00167.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Elvevold, K. Articles by Martinez, I. Search for Related Content PubMed PubMed Citation Articles by Elvevold, K. Articles by Martinez, I.

INVITED REVIEWS

The liver sinusoidal endothelial cell: a cell type of controversial and confusing identity

¹Department of Cell Biology and Histology, Institute of Medical Biology; ²Department of Orthopaedic Surgery, Institute of Clinical Medicine, University of Tromsø, Tromsø, Norway

Submitted 16 April 2007 ; accepted in final form 30 November 2007

	ABSTRACT

TOP ABSTRACT REFERENCES

 
A look through the literature on liver sinusoidal endothelial cells (LSECs) reveals that there are several conflicts among different authors of what this cell type is and does. Major controversies that will be highlighted in this review include aspects of the physiological role, the characterization, and the protocols of isolation and cultivation of these cells. Many of these conflicts may be ascribed to the fact that the cell was only recently established as a distinct cell type and that researchers from different disciplines tend to define their structure and function differently. This field is in need of a common platform to obtain a sound communication and a unified understanding of how to interpret novel research results. The aim of this review is to encourage scientists not to ignore the fact that there are, indeed, different opinions in the literature on LSECs. We also hope that this review will point out to the reader that some issues that may seem well established regarding our knowledge about the LSECs, in reality, are still unresolved and, indeed, controversial.

reticuloendothelial system; identification; endocytosis; serum

The study of LSECs is a rather young field; in fact, the first studies on LSECs can be traced back only about 35 years, when Eddie Wisse for the first time presented convincing evidence that the LSEC represents a distinct cell type (85). Wisse showed that open fenestration without a diaphragm or basement membrane is a typical feature of LSECs. He also was the first to report that LSECs contained unusually high amounts of endocytic vesicles and suggested that they were engaged in uptake of protein from blood passing through the sinusoids. The first physiological macromolecule shown to be cleared from the circulation by LSECs was hyaluronan (18, 71). This marked the start of a series of experiments culminating in the notion that LSECs are a specialized type of scavenger endothelium that uses clathrin-mediated endocytosis to clear an array of physiological and foreign macromolecules and colloids from the blood (73). Until about 1990, most of these studies were performed by scientists that had a special interest in the biology of these cells. Most of these researchers were well informed about the young history of this field of research and were open to new ways of classifying LSECs. After about 1990 the general interest in LSECs increased, and the number of scientists that were not raised in the tradition of cells of the liver sinusoid started to grow. With an increased number of scientists coming in from other disciplines (cancer, immunology, virology, pharmacology, hematology, and more), showing an interest to include LSECs in their studies, there has been an increasing tendency to find in the literature conflicting descriptions on LSECs. The understanding of what the LSEC is and does and how to identify and distinguish it is not always obvious to new scientists in this field. The present review aims to point out the major controversies associated with studies on LSECs. Knowledge about the existing conflicts is a prerequisite to understand the field and a sound way to prepare for a future unitary view. Here we will focus on the following four major issues of LSEC controversies: 1) ignored issues related to the role of LSECs in blood clearance, 2) discrepancies in identification of LSECs, 3) controversies associated with isolation and cultivation of LSECs, and 4) the confusing role of LSECs in immunity.

Ignored Issues Related to the Role of LSECs in Blood Clearance

The following statements, commonly found in the literature, are in conflict with each other: 1) the hepatic reticuloendothelial system (RES) clears waste from the circulation, 2) the hepatic RES is equal to Kupffer cells (KCs), and 3) the LSEC represents the cell type that is mainly responsible for the clearance of most colloids and soluble waste macromolecules from the circulation. How can we comprehend these incompatible statements? The answer lies in knowledge about the history of research on RES and certain key concepts dealing with how cells internalize matter.

Phagocytosis or pinocytosis: a problem of semantics. Although regarded by many as an old-fashioned and ill-defined term, the RES is still a frequently used expression. The RES was for a long time commonly understood as just an alternative way of naming the mononuclear phagocyte system (MPS), or macrophage system. Although recent studies clearly show that a major arm of the RES consists of the LSECs, authors of most text books and scientific publications still ignore this fact and continue to bring forward the erroneous understanding that RES and MPS are synonymous terms. As will be shown in the following, the way we today understand terms that were launched more than a century ago plays a central role to explain how this conflict came to be. More than a century ago, Eli Metchnikoff introduced two terms that are still in use and form important parts of the specialized vocabulary of cell biologists: "macrophage" ("cell type that eats a lot") and "phagocytosis" ("engulfment of material, often associated with macrophages") (54). Thus it is logical and correct to associate MPS with the specialized process of phagocytosis. However, Metchnikoff did not define phagocytosis the way we do today. The idea of dividing cellular uptake into phagocytosis and pinocytosis was not introduced until 1931 when Lewis launched the concept of pinocytosis to describe the special process internalizing solutes and soluble material (48). Thus Metchnikoff and his contemporaries defined phagocytosis without reference to the physical state of the material to be taken up. This circumstance, combined with the fact that the term RES was also introduced before the idea of pinocytosis appeared and that the universal view that cells of RES generally used phagocytosis to take up material from the circulation, led to the conflict or confusion that was so clearly expressed by Ralph van Furth, who around 1970 advised that there is no need to keep the old-fashioned term RES, since the MPS covers more precisely the structure and function of RES (82). The establishment of the LSEC as a cell type distinct from the KC (85), combined with the discovery during the 1980s that LSECs represent a major scavenger cell system in liver, led Kawai and coworkers (36) to suspect that van Furth's advice might be misleading and decided to repeat the experimental protocol used a century ago to identify the cell system known today as RES. Using the original protocol of administering the colloidal vital stain lithium carmine (one of the most frequently used test substances employed around a century ago to study the RES) and using modern methodology to identify the cells that accumulated the dye, Kawai et al. were able to show that the cells that most efficiently accumulated vital stain in the liver were the LSECs but not the liver macrophages or KCs. Just as important, present-day research has revealed that the two cell types differ functionally based on their uptake preferences: LSECs do not normally perform phagocytosis but are extremely active in uptake of soluble or colloidal materials, whereas the KCs are geared to uptake of larger particles (see the following section).

Size matters. A study on rat LSECs concluded that the cells are not able to engulf particles greater than 0.23 µm under normal conditions, whereas the KCs take up larger particles (69). However, when the phagocytic function of KCs was impaired, they found that LSECs took up particles larger than 1 µm. Although colloids are too small in size to be taken up by phagocytosis in macrophages, colloidal carbon, probably the most frequently used RES test substance, accumulates primarily in KCs upon intravenous injection. This would appear to contradict the rule that large particles are home to KCs, whereas colloids and soluble macromolecules end up in LSECs. However, Donald reported in 1975 (13) that colloidal carbon rapidly sticks to platelets and activates them to form aggregates. Such free or aggregated platelets, with large amounts of colloidal carbon attached to them, are rapidly taken up by phagocytosis in KCs. Present-day scientists should realize that colloidal carbon interacts very differently than other vital stains with the blood and RES. If Donald's report on the unusual interaction of colloidal carbon with platelets had been considered by authors on RES, we might have avoided the misconception that colloidal carbon behaves like most other vital stains in its interaction with RES.

It is common to find that present-day studies on LSECs do not take into consideration the special scavenger features of these cells. A recent enzyme replacement therapy report described the use of mannose receptor-deficient mice to study the distribution of acid lipase that was injected intravenously (14). Immunohistochemistry performed on liver sections was, by the use of light microscope, interpreted to mean that the enzyme was taken up foremost in KCs. This conclusion was drawn without any further attempt to distinguish between KCs and LSECs and is in contrast to a number of other studies where other injected lysosomal enzymes were observed to be taken up foremost in LSECs (2, 30, 72). Knowing that acid lipase is a soluble molecule, it is doubtful that it is mainly cleared from the circulation by phagocytosis. Furthermore, the use of plain light/fluorescence microscopy of liver sections following intravenous administration of stained material does not allow a clear distinction among sinusoidal liver cells. It may be found in the literature that staining along the sinusoids is taken to prove uptake in either LSECs or KCs, or both. To illustrate such typical staining patterns we have included a figure showing fluorescence micrographs of liver sections following intravenous injections of a tetramethylrhodamine isothiocyanate (TRITC)-labeled soluble ligand and FITC-labeled particles (Fig. 1). In the example shown in the figure, we have injected soluble TRITC-labeled formaldehyde-treated serum albumin (TRITC-FSA) and FITC-labeled beads (2 µm). Some authors would claim that continuous staining along the sinusoids (Fig. 1B) represents uptake in KCs. Other authors would argue that the same staining pattern is typical of LSECs. Knowing that FSA and 2-µm particles distinguish LSECs and KCs (32, 60), it is advisable to employ coinjection with fluorescently labeled FSA and particles when the goal is to localize and identify the type(s) of hepatic cells responsible for uptake of certain materials.

View larger version (44K): [in this window] [in a new window]   Fig. 1. Fluorescence micrographs of a rat liver section following double intravenous administration of 0.5 mg tetramethylrhodamine isothiocyanate (TRITC)-labeled formaldehyde-treated serum albumin (TRITC-FSA), a substance known to be taken up by liver sinusoidal endothelial cells (LSECs) (32) (A), and 5 x 108 FITC-labeled beads (2-µm diameter), known to be taken up exclusively in Kupffer cells (KCs) (60) (B). Both probes can be observed to have accumulated along the sinusoids. By superimposing A and B, it can be seen that the beads have accumulated in sites that do not coincide with the presence of TRITC-FSA (C).

Discrepancies in Identification of LSECs

Membrane markers. During the 1970s and 80s, some laboratories reported the existence of membrane molecules that specifically stained endothelia of numerous organs, including both large vessels and capillaries (26, 33, 59, 81, 84). Since then, these markers have been frequently used by many laboratories to characterize endothelial cells in different tissues and species. The expression of many of these marker molecules by LSECs remains controversial (Table 1). Experiments in vitro have revealed discrepancies in the expression of CD31, von Willebrand factor (vWF), CD106, and immunomarkers such as major histocompatibility complex (MHC) class II, CD4, CD40, CD80, and CD86 in different species. Expression of vWF has been generally reported on human liver sections, whereas in cultured human LSECs the expression of this marker has been variably detected. This shows that there are differences between in vivo and in vitro observations in addition to differences between species. Another controversial LSEC marker is CD31. Electron microscopic studies in rat showed that CD31 is located intracellularly shortly after establishing cultures but later, after defenestration, CD31 is expressed on the surface as in conventional endothelial cells (10). Thus immunohistochemistry gives positive staining for CD31 in LSECs in liver sections, whereas freshly isolated LSECs do not stain for CD31 unless the cells are permeabilized before staining. The absence or presence of surface markers in LSECs is of major importance in immunomagnetic isolation of the cells. This issue will be discussed in greater detail in the section dealing with isolation and cultivation. Of note, certain treatments of animals may induce the expression of markers that are not normally present on LSECs. For instance, injection of colloidal carbon have been observed to induce the expression of vWF in LSECs in vivo (37). Variation in the expression of most of these molecules by LSECs has been observed during the development of certain liver diseases including chronic inflammatory disorders, fibrosis, viral infection, or tumor development (19, 23–25, 79, 80, 83, 87, 88). Normal aging is associated with sinusoidal capillarization (5, 9, 31, 47), leading to changes in the expression of marker molecules along the sinusoidal endothelium. This fact is not often taken into consideration in studies of human liver that frequently involve samples from individuals of different age. The presence of markers normally associated with cells of the immune system will be discussed later.

View larger version (60K): [in this window] [in a new window]   Fig. 2. Scanning electron micrographs of fenestration on LSECs. A and B are cultured on fibronectin-coated glass slides, whereas C shows the liver sinusoids with numerous fenestrae. Freshly isolated cells (A) show a well-defined and organized appearance of fenestrae in sieve plates (circle), whereas after 1 day in culture (B), the cells are largely defenestrated, and only sporadic fenestrae in sieve plates are observed (circle). Transcytoplasmic holes are observed (arrows), but these structures are most likely artefacts resulting from the preparation of the specimens and should be cautiously interpreted. N = nucleus; bars are 2 µm.

Under normal conditions LSECs employ only receptor-mediated endocytosis to eliminate soluble or colloidal substances smaller than 0.23 µm (69). Under any circumstance, it would seem useless to employ phagocytosis as a functional marker of LSECs, given the fact that they are located next to the KCs, the body's largest population of macrophages.

Uptake of soluble macromolecules. A unique feature of LSECs is their high capacity to eliminate colloids and soluble waste macromolecules from the circulation. Although this function can be used as a reliable marker to identify LSECs, it is important to be aware of the fact that every cell in the body is in principle able to perform endocytosis. However, the unsurpassed speed and capacity of endocytosis in LSECs set these cells apart from all other cell types. By challenging LSECs for a limited period (<20 min) (16) and with low amounts of ligand (<10 µg/ml), only this cell type will endocytose detectable amounts of the ligand. Of note, it is not uncommon to see in the literature that LSECs claim to be functionally identified by endocytosis by using ligand concentrations in the order of mg/ml and incubating periods of several hours. Clearly, under such conditions many cell types will accumulate detectable levels of ligand, which will make it difficult to distinguish LSECs. It should be noted that the characteristic high-activity receptor-mediated endocytosis is rapidly lost in cultured LSECs. This phenomenon is particularly prominent in rodents (Fig. 4).

View larger version (7K): [in this window] [in a new window]   Fig. 4. Progressive loss of endocytic capacity by LSECs in culture. Freshly isolated LSECs show high capacity for internalization and degradation of radioactively labeled FSA, a ligand for the scavenger receptor. This specific LSEC function is gradually lost with time in culture and disappears faster in LSEC cultures from small vertebrates like rodents (A) than larger vertebrates like pigs (B).

New markers related to specific LSEC functions. A new member of the scavenger receptor family that is expressed exclusively on the surface of LSECs is stabilin-2 (22), also called the liver hyaluronan receptor. Lymphatic vessel endothelial hyaluronan receptor (LYVE-1) is another member of the scavenger receptor family that is constitutively expressed on LSECs and absent on other hepatic cells and conventional endothelium (58). Recent literature has identified two new lectins expressed on LSECs. Liver/lymph node-specific ICAM-3-grabbing nonintegrin (L-SIGN) (1, 44, 74) is strongly and constitutively expressed on LSECs and lymph node endothelium but not on other hepatic cells or other endothelia. Liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin) has been shown to have the same cellular distribution and similar binding capacities as L-SIGN (12, 49). These new marker molecules claimed to be exclusively expressed on LSECs were described only very recently, and since the literature on these markers is still rather limited, the use of these new marker molecules to identify LSECs should be carried out with some caution.

Controversies Associated With Isolation and Cultivation of LSECs

Isolation. Detailed studies on LSECs require reliable methods for cell isolation and cultivation. The first paper describing immunoisolation of LSECs was published in 2002 (77). By using the LSEC-specific antibody SE-1, 98% pure rat LSECs were reported. Unfortunately this monoclonal antibody has so far not been commercially available. In a series of experiments where LSECs were isolated by counterflow elutriation, Knolle and coworkers (41, 42) reported that LSECs function as antigen-presenting cells (APC). However, by using immunomagnetic beads to remove CD45⁺ KCs and CD11b⁺ dendritic cells (DC) to obtain highly purified LSECs, Katz et al. (35) found no evidence of antigen-presenting function of the highly purified LSECs and speculated that the contradictory results might be explained by the possibility that Knolle and coworkers used LSEC preparations that were contaminated by other cell types. Recently, the isolation methods used by both Katz and coworkers and Knolle and coworkers were questioned by Onoe et al. (62), who employed the membrane marker CD105⁺ for positive selection of LSECs by using MACS. Onoe et al. used positive selection to obtain their cells, whereas Katz and coworkers obtained their LSECs by negative selection. However, CD105 is also expressed on liver stellate cells and myofibroblasts (55), and it has been advised to exercise caution when using this marker to identify or purify LSECs (46). Another endothelial cell marker, CD31, has been used for immunomagnetic isolation of human LSECs (45). However, in rat, the selection of CD31-positive cells yielded a population of LSECs with fewer fenestrae than LSECs isolated by elutriation (11). The latter study concluded that "cells isolated by anti-CD31 and immunomagnetic sorting lacked the hallmark features of LSEC." Although all isolation methods mentioned above may yield high relative proportions of LSECs, it is likely that the degree of purity of LSECs and the main contaminating cell types vary from one method to the other.

Cultivation. Cultivation procedures may represent the chief source of conflict in the studies on LSECs today. Some laboratories culture LSECs under conditions that allow cell proliferation and subsequent splitting and passaging before the cells are used in experiments several days or even weeks after the isolation (34, 64). This frequently used practice is associated with conflicts that can be sorted in two "schools," 1) the one claiming that LSEC features can only be studied in short-term (true primary) culture and 2) the one that frequently makes use of long-term cultures (including use of cell lines). Although these schools rarely, if ever, discuss openly their disagreements, it appears important to point out this conflict. To illustrate this, we show some of the contradictory statements that are often seen in the literature related to time of cultivation of LSECs: 1) LSEC cultures can be propagated by trypsin splitting and subcultivation (21, 34, 64); 2) studies on LSECs can be performed using cell lines originating from native LSECs (53, 64); 3) important features of LSECs, such as scavenger function and fenestration, are severely decreased or disappear completely in LSECs that are cultivated for more than 1–2 days (15, 43, 61); 4) serum (5–20%), which is normally supplemented in long-term cultures of cells (and often also in short-term primary cultures), has been noted to act toxic to dividing LSECs (43, 61); 5) LSECs proliferate only very slowly or not at all in culture (15, 43).

A fact that is often underscored is that many phenotypic features of LSECs change gradually when the cells are placed in a culture dish, and most importantly, many of the signature functions of LSECs are also rapidly lost during in vitro culture (15, 43) (see also Figs. 2 and 4). The drastic change in environment associated with the transfer of the LSECs from the intact liver to culture conditions is clearly responsible for many of these alterations. The use of light microscopy to determine the quality of a LSEC culture is at best semioptimal. In Fig. 3B, the 3-day-old cells appear very similar to the fresh cells in Fig. 3A. However, ultrastructural studies by scanning electron microscopy reveal a clear loss of fenestrae already after 1 day (Fig. 2B). In addition, the very high endocytic activity is lost after some days in culture (Fig. 4). Given that serum is lethal to dividing LSECs (43), the cultures propagated in the presence of serum will gradually change from being composed of mainly LSECs to a stromal-like culture (Fig. 3C). This puts forward the following questions: should serum be used to cultivate LSECs? How soon after seeding of freshly isolated LSECs should experiments be carried out on these cells? Do the results obtained with long-term cultivated LSECs reflect the function of these cells in the intact liver? How is the term "primary culture of LSECs" defined? Is there a possibility that cells taken to represent proliferating LSECs are instead contaminating nonsinusoidal or nonendothelial cells? If some authors claim that LSECs do not proliferate in vitro, then how come other authors use terms like "subcultivation of LSECs" and "LSECs grown to confluence"? Do LSECs from different species differ in their proliferative potential? How come some authors use LSEC cell lines when other authors claim that cell lines that originate from primary LSEC cultures have lost their original scavenger activity and fenestration? Finally, how many specialized differentiated LSEC characteristics can be lost before the cells loose their status as LSECs?

View larger version (87K): [in this window] [in a new window]   Fig. 3. Effect of serum on primary rat LSECs cultured on fibronectin-coated dishes. LSECs were cultivated for 12 h (A), and then 3 days in a special serum-free medium (B) (16), or 3 days in RPMI 1640 medium containing 10% fetal calf serum (C). The morphology of the cells in the serum-free medium (B) is very similar to the cells at early phases of culture (A). However, incubation in the presence of serum for longer periods (C) had dramatic negative effects on the viability of LSECs, also favoring the growth of contaminating fibroblast-like cells (arrows) and/or other types of endothelial cells (arrowheads).

The Confusing Role of LSECs in Immunity

The liver is enriched in macrophages (KCs), natural killer (NK) cells, and NKT cells, which have traditionally been regarded as key cellular components of the innate immune system. However, the LSEC also promotes active antigen uptake via its Fc- receptor and pattern recognition receptors such as the mannose receptor and scavenger receptor. For this reason alone, these cells must be considered as an important part of the innate immune system. In recent years the LSECs have also been implicated as inducers of tolerance in the liver. In a series of experiments, Knolle and coworkers reported that LSECs express molecules that promote antigen presentation, including MHC class I and II and the costimulatory molecules CD40, CD80, and CD86, in addition to their endocytic scavenger receptors (reviewed in Ref.39). LSECs were reported to perform receptor-mediated endocytosis and/or phagocytosis, antigen processing, and presentation with similar efficacy as those of DCs. In contrast to conventional APC populations, LSECs failed to induce differentiation of naive CD4⁺ T cells toward a T_h1 phenotype but promoted development of T_h0 cells. The failure of LSECs to induce differentiation toward T_h1, together with the production of negative immunomodulatory cytokines by LSEC-primed T cells upon restimulation, was thought to contribute to the unique hepatic immune tolerance (7). In this model, the LSEC represented the sessile, organ-resident APC-inducing local tolerance in the liver towards soluble antigens such as food antigens or self proteins. The liver DCs were thought to take up antigen in the liver as well and then migrate to local lymph nodes, mediating immune tolerance in the lymphoid compartment. This view of LSECs as functional APC was seriously challenged by Katz et al. (35), who employed new efficient separation techniques to obtain highly purified LSEC cultures. They found that, unlike DCs, LSECs had low or absent expression of MHC class II, CD86, and CD11c. However, they found that LSECs demonstrated a high capacity for antigen uptake in vitro and in vivo, and although uptake of AcLDL has been reported to be a specific function of the LSEC, they found that DCs captured AcLDL to a similar extent in vivo. Consistent with their phenotype, LSECs were poor stimulators of allogeneic T cells. Furthermore, in the absence of exogenous costimulation, Katz et al. found that LSECs induced negligible proliferation of CD4⁺ or CD8⁺ TCR-transgenic T cells. They concluded that LSECs alone are insufficient to activate naive T cells. A year later, a study by Onoe et al. (62), contradictory to the results of Katz et al. but in agreement with Knolle and coworkers, concluded that primary LSECs from mice do, indeed, express MHC class II and CD86 but not CD11c. The contradictory findings were believed to occur due to the separation technique used by Katz et al. that, according to Onoe, was unsatisfactory (as mentioned in section III above). However, selection of CD105⁺ cells as used by Onoe may not result in pure LSECs as indicated by others (46) because this marker is also expressed on liver stellate cells (55). It is also very important to note that the length of cultivation and presence of serum were different in the studies reported by Knolle, Katz, and Onoe groups. These parameters have been shown previously to seriously affect the outcome of LSEC studies.

Recently it was reported that LSECs endocytose splenocytes injected via the portal vein. The LSECs that endocytosed the splenocytes showed enhanced expression of MHC class II molecules and CD80 (78). Of note, the notion that LSECs are capable of endocytosing/phagocytosing splenocytes is in contrast to the general concept that the cells under normal conditions do not take up material exceeding 0.23 µm (69). The finding that neutrophils are removed by KCs and not by LSECs is in agreement with this notion (68). On this basis, it is difficult to explain LSEC phagocytosis of splenocytes.

The conflicts associated with the expression of MHC class II in LSECs is further underlined by a number of earlier studies that failed to demonstrate this molecule on rat or human LSECs (36, 50, 66) (see also Table 1). Obviously, further studies are needed to elucidate the role of LSECs in the immune system.

Conclusions

The study of LSECs is still a young discipline. Different laboratories have different opinions about the identity of LSECs, and therefore design methods and interpret results differently. Some of the conflicting views can be readily identified and discussed in a scientific way. But other conflicting issues are based on the fact that some authors do not even appreciate those issues of conflict that other authors identify as highly conflicting.

Role in blood clearance. A large body of evidence strongly suggests that the two major scavenger cell types of liver are KCs, which take up particulate matter, and LSECs that clear soluble macromolecules and colloids of size <0.23 µm. However, most authors of textbooks and scientific publications still ignore this and maintain the old notion that "hepatic RES = KCs." A meaningful further development of this field is difficult unless the correct notion (the hepatic RES = LSECs + KCs) is generally accepted.

Identification. Some markers used to identify LSECs are also expressed on KCs, stellate cells, or endothelial cells from different vascular beds and are therefore inadequate as LSEC-specific markers. In addition, phenotypic and functional variations are observed in LSECs from diseased livers, as well as in healthy livers of different age groups. Characterization of LSECs based on their unique scavenger function seems to be a reliable approach; however, caution should be taken for choosing the adequate experimental settings.

Isolation and cultivation. Some authors use long-term cultures and cell lines and subcultivate LSECs, whereas other authors claim that LSECs loose their unique native characteristics upon cultivation for more than 1–2 days and differ too much from native LSECs. Some authors cultivate LSECs in medium with serum, whereas others claim that serum is toxic to the cells. Clearly, the results of in vitro experiments depend on, to a large extent, the isolation and cultivation procedures used by the different authors.

Role in immunity. Some authors claim that LSECs carry MHC class II molecules and present antigens to generate hepatic immune tolerance. Other authors have not found evidence that LSECs express MHC class II or present antigens. These conflicts are largely based on different views on isolation and cultivation procedures.

The present review was written to remind scientists dealing with LSECs about the important controversies that still exist regarding these cells. Both old scholars and new scientists entering the field should consider that some issues that may seem well established regarding our knowledge about the LSECs are in reality still unresolved and controversial.

	ACKNOWLEDGMENTS

 
The excellent assistance by Cristina Øie is greatly appreciated. This work was supported in part by the Norwegian Research Council, The Norwegian Cancer Association, and the Medical Faculty, University of Tromsø.

	FOOTNOTES

 

Address for reprint requests and other correspondence: Bård Smedsrød, Dept. of Cell Biology and Histology, Institute of Medical Biology, Univ. of Tromsø, 9037 Tromsø, Norway (e-mail: bard.smedsrod{at}fagmed.uit.no)

	REFERENCES

TOP ABSTRACT REFERENCES

 

1. Bashirova AA, Geijtenbeek TB, van Duijnhoven GC, van Vliet SJ, Eilering JB, Martin MP, Wu L, Martin TD, Viebig N, Knolle PA, KewalRamani VN, van Kooyk Y, Carrington M. A dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN)-related protein is highly expressed on human liver sinusoidal endothelial cells and promotes HIV-1 infection. J Exp Med 193: 671–678, 2001.[Abstract/Free Full Text]
2. Bijsterbosch MK, Donker W, van de Bilt H, van Weely S, van Berkel TJ, Aerts JM. Quantitative analysis of the targeting of mannose-terminal glucocerebrosidase. Predominant uptake by liver endothelial cells. Eur J Biochem 237: 344–349, 1996.[Web of Science][Medline]
3. Braet F, Wisse E. Structural and functional aspects of liver sinusoidal endothelial cell fenestrae: a review. Comp Hepatol 1: 1, 2002.[CrossRef][Medline]
4. Breiner KM, Schaller H, Knolle PA. Endothelial cell-mediated uptake of a hepatitis B virus: a new concept of liver targeting of hepatotropic microorganisms. Hepatology 34: 803–808, 2001.[CrossRef][Web of Science][Medline]
5. Cogger VC, Warren A, Fraser R, Ngu M, McLean AJ, Le Couteur DG. Hepatic sinusoidal pseudocapillarization with aging in the nonhuman primate. Exp Gerontol 38: 1101–1107, 2003.[CrossRef][Web of Science][Medline]
6. Crettaz J, Berraondo P, Mauleon I, Ochoa L, Shankar V, Barajas M, van Rooijen N, Kochanek S, Qian C, Prieto J, Hernandez-Alcoceba R, Gonzalez-Aseguinolaza G. Intrahepatic injection of adenovirus reduces inflammation and increases gene transfer and therapeutic effect in mice. Hepatology 44: 623–632, 2006.[CrossRef][Medline]
7. Crispe IN. Hepatic T cells and liver tolerance. Nat Rev Immunol 3: 51–62, 2003.[CrossRef][Web of Science][Medline]
8. Daneker GW, Lund SA, Caughman SW, Swerlick RA, Fischer AH, Staley CA, Ades EW. Culture and characterization of sinusoidal endothelial cells isolated from human liver. In Vitro Cell Dev Biol Anim 34: 370–377, 1998.[Medline]
9. De Leeuw AM, Brouwer A, Knook DL. Sinusoidal endothelial cells of the liver: fine structure and function in relation to age. J Electron Microsc Tech 14: 218–236, 1990.[CrossRef][Medline]
10. DeLeve LD, Wang X, Hu L, McCuskey MK, McCuskey RS. Rat liver sinusoidal endothelial cell phenotype is maintained by paracrine and autocrine regulation. Am J Physiol Gastrointest Liver Physiol 287: G757–G763, 2004.[Abstract/Free Full Text]
11. Deleve LD, Wang X, McCuskey MK, McCuskey RS. Rat liver endothelial cells isolated by anti-CD31 immunomagnetic separation lack fenestrae and sieve plates. Am J Physiol Gastrointest Liver Physiol 291: G1187–G1189, 2006.[Abstract/Free Full Text]
12. Dominguez-Soto A, Aragoneses-Fenoll L, Martin-Gayo E, Martinez-Prats L, Colmenares M, Naranjo-Gomez M, Borras FE, Munoz P, Zubiaur M, Toribio ML, Delgado R, Corbi AL. The DC-SIGN-related lectin LSECtin mediates antigen capture and pathogen binding by human myeloid cells. Blood 109: 5337–5345, 2007.[Abstract/Free Full Text]
13. Donald KJ, Tennent RJ. The relative roles of platelets and macrophages in clearing particles from the blood; the value of carbon clearance as a measure of reticuloendothelial phagocytosis. J Pathol 117: 235–245, 1975.[CrossRef][Medline]
14. Du H, Levine M, Ganesa C, Witte DP, Cole ES, Grabowski GA. The role of mannosylated enzyme and the mannose receptor in enzyme replacement therapy. Am J Hum Genet 77: 1061–1074, 2005.[CrossRef][Web of Science][Medline]
15. Elvevold K, Nedredal GI, Revhaug A, Bertheussen K, Smedsrod B. Long-term preservation of high endocytic activity in primary cultures of pig liver sinusoidal endothelial cells. Eur J Cell Biol 84: 749–764, 2005.[CrossRef][Web of Science][Medline]
16. Elvevold KH, Nedredal GI, Revhaug A, Smedsrod B. Scavenger properties of cultivated pig liver endothelial cells. Comp Hepatol 3: 4, 2004.[CrossRef][Medline]
17. Esser S, Wolburg K, Wolburg H, Breier G, Kurzchalia T, Risau W. Vascular endothelial growth factor induces endothelial fenestrations in vitro. J Cell Biol 140: 947–959, 1998.[Abstract/Free Full Text]
18. Fraser JR, Alcorn D, Laurent TC, Robinson AD, Ryan GB. Uptake of circulating hyaluronic acid by the rat liver. Cellular localization in situ. Cell Tissue Res 242: 505–510, 1985.[CrossRef][Web of Science][Medline]
19. Fukuda Y, Nagura H, Imoto M, Koyama Y. Immunohistochemical studies on structural changes of the hepatic lobules in chronic liver diseases. Am J Gastroenterol 81: 1149–1155, 1986.[Medline]
20. Funyu J, Mochida S, Inao M, Matsui A, Fujiwara K. VEGF can act as vascular permeability factor in the hepatic sinusoids through upregulation of porosity of endothelial cells. Biochem Biophys Res Commun 280: 481–485, 2001.[CrossRef][Medline]
21. Gerlach JC, Zeilinger K, Spatkowski G, Hentschel F, Schnoy N, Kolbeck S, Schindler RK, Neuhaus P. Large-scale isolation of sinusoidal endothelial cells from pig and human liver. J Surg Res 100: 39–45, 2001.[CrossRef][Medline]
22. Hansen B, Longati P, Elvevold K, Nedredal GI, Schledzewski K, Olsen R, Falkowski M, Kzhyshkowska J, Carlsson F, Johansson S, Smedsrod B, Goerdt S, McCourt P. Stabilin-1 and stabilin-2 are both directed into the early endocytic pathway in hepatic sinusoidal endothelium via interactions with clathrin/AP-2, independent of ligand binding. Exp Cell Res 303: 160–173, 2005.[CrossRef][Web of Science][Medline]
23. Hao J, Shi J, Ren W, Han G, Zhu J, Wang S, Xie Y. Hepatic microcirculatory disturbances in patients with chronic hepatitis B. Chin Med J (Engl) 115: 65–68, 2002.[Medline]
24. Hattori M, Fukuda Y, Imoto M, Koyama Y, Nakano I, Urano F. Histochemical properties of vascular and sinusoidal endothelial cells in liver diseases. Gastroenterol Jpn 26: 336–343, 1991.[Medline]
25. Hollestelle MJ, Geertzen HG, Straatsburg IH, van Gulik TM, van Mourik JA. Factor VIII expression in liver disease. Thromb Haemost 91: 267–275, 2004.[Medline]
26. Holthofer H, Virtanen I, Kariniemi AL, Hormia M, Linder E, Miettinen A. Ulex europaeus I lectin as a marker for vascular endothelium in human tissues. Lab Invest 47: 60–66, 1982.[Web of Science][Medline]
27. Horn T, Christoffersen P, Henriksen JH. Alcoholic liver injury: defenestration in noncirrhotic livers—a scanning electron microscopic study. Hepatology 7: 77–82, 1987.[Web of Science][Medline]
28. Inchley CJ. The activity of mouse Kupffer cells following intravenous injection of T4 bacteriophage. Clin Exp Immunol 5: 173–187, 1969.[Medline]
29. Irving MG, Roll FJ, Huang S, Bissell DM. Characterization and culture of sinusoidal endothelium from normal rat liver: lipoprotein uptake and collagen phenotype. Gastroenterology 87: 1233–1247, 1984.[Web of Science][Medline]
30. Isaksson A, Hultberg B, Sundler R, Akesson B. Uptake of beta-hexosaminidase by nonparenchymal liver cells and peritoneal macrophages. Enzymes 30: 230–238, 1983.[Medline]
31. Jamieson HA, Hilmer SN, Cogger VC, Warren A, Cheluvappa R, Abernethy DR, Everitt AV, Fraser R, de Cabo R, Le Couteur DG. Caloric restriction reduces age-related pseudocapillarization of the hepatic sinusoid. Exp Gerontol 42: 374–378, 2007.[CrossRef][Medline]
32. Jansen RW, Molema G, Harms G, Kruijt JK, van Berkel TJ, Hardonk MJ, Meijer DK. Formaldehyde treated albumin contains monomeric and polymeric forms that are differently cleared by endothelial and Kupffer cells of the liver: evidence for scavenger receptor heterogeneity. Biochem Biophys Res Commun 180: 23–32, 1991.[CrossRef][Web of Science][Medline]
33. Jones TR, Kao KJ, Pizzo SV, Bigner DD. Endothelial cell surface expression and binding of factor VIII/von Willebrand factor. Am J Pathol 103: 304–308, 1981.[Abstract]
34. Karrar A, Broome U, Uzunel M, Qureshi AR, Sumitran-Holgersson S. Human liver sinusoidal endothelial cells induce apoptosis in activated T cells: a role in tolerance induction. Gut 56: 243–252, 2006.[Web of Science][Medline]
35. Katz SC, Pillarisetty VG, Bleier JI, Shah AB, DeMatteo RP. Liver sinusoidal endothelial cells are insufficient to activate T cells. J Immunol 173: 230–235, 2004.[Abstract/Free Full Text]
36. Kawai Y, Smedsrod B, Elvevold K, Wake K. Uptake of lithium carmine by sinusoidal endothelial and Kupffer cells of the rat liver: new insights into the classical vital staining and the reticulo-endothelial system. Cell Tissue Res 292: 395–410, 1998.[CrossRef][Medline]
37. Khandoga A, Stampfl A, Takenaka S, Schulz H, Radykewicz R, Kreyling W, Krombach F. Ultrafine particles exert prothrombotic but not inflammatory effects on the hepatic microcirculation in healthy mice in vivo. Circulation 109: 1320–1325, 2004.[Abstract/Free Full Text]
38. Kirn A, Steffan AM, Anton M, Gendrault JL, Bingen A. Phagocytic properties displayed by mouse hepatocytes after virus induced damage of the sinusoidal lining. Biomedicine (Paris) 29: 25–28, 1978.
39. Knolle PA, Gerken G. Local control of the immune response in the liver. Immunol Rev 174: 21–34, 2000.[CrossRef][Web of Science][Medline]
40. Knolle PA, Germann T, Treichel U, Uhrig A, Schmitt E, Hegenbarth S, Lohse AW, Gerken G. Endotoxin down-regulates T cell activation by antigen-presenting liver sinusoidal endothelial cells. J Immunol 162: 1401–1407, 1999.[Abstract/Free Full Text]
41. Knolle PA, Limmer A. Neighborhood politics: the immunoregulatory function of organ-resident liver endothelial cells. Trends Immunol 22: 432–437, 2001.[CrossRef][Web of Science][Medline]
42. Knolle PA, Schmitt E, Jin S, Germann T, Duchmann R, Hegenbarth S, Gerken G, Lohse AW. Induction of cytokine production in naive CD4⁺ T cells by antigen-presenting murine liver sinusoidal endothelial cells but failure to induce differentiation toward Th1 cells. Gastroenterology 116: 1428–1440, 1999.[CrossRef][Web of Science][Medline]
43. Krause P, Markus PM, Schwartz P, Unthan-Fechner K, Pestel S, Fandrey J, Probst I. Hepatocyte-supported serum-free culture of rat liver sinusoidal endothelial cells. J Hepatol 32: 718–726, 2000.[CrossRef][Medline]
44. Lai WK, Sun PJ, Zhang J, Jennings A, Lalor PF, Hubscher S, McKeating JA, Adams DH. Expression of DC-SIGN and DC-SIGNR on human sinusoidal endothelium: a role for capturing hepatitis C virus particles. Am J Pathol 169: 200–208, 2006.[Abstract/Free Full Text]
45. Lalor PF, Edwards S, McNab G, Salmi M, Jalkanen S, Adams DH. Vascular adhesion protein-1 mediates adhesion and transmigration of lymphocytes on human hepatic endothelial cells. J Immunol 169: 983–992, 2002.[Abstract/Free Full Text]
46. Lalor PF, Lai WK, Curbishley SM, Shetty S, Adams DH. Human hepatic sinusoidal endothelial cells can be distinguished by expression of phenotypic markers related to their specialised functions in vivo. World J Gastroenterol 12: 5429–5439, 2006.[Medline]
47. Le Couteur DG, Fraser R, Hilmer S, Rivory LP, McLean AJ. The hepatic sinusoid in aging and cirrhosis: effects on hepatic substrate disposition and drug clearance. Clin Pharmacokinet 44: 187–200, 2005.[CrossRef][Web of Science][Medline]
48. Lewis WHR. Pinocytosis. Bull John Hopkins Hosp 49: 17–26, 1931.[Web of Science]
49. Liu W, Tang L, Zhang G, Wei H, Cui Y, Guo L, Gou Z, Chen X, Jiang D, Zhu Y, Kang G, He F. Characterization of a novel C-type lectin-like gene, LSECtin: demonstration of carbohydrate binding and expression in sinusoidal endothelial cells of liver and lymph node. J Biol Chem 279: 18748–18758, 2004.[Abstract/Free Full Text]
50. Lovdal T, Andersen E, Brech A, Berg T. Fc receptor mediated endocytosis of small soluble immunoglobulin G immune complexes in Kupffer and endothelial cells from rat liver. J Cell Sci 113: 3255–3266, 2000.[Abstract]
51. Mak KM, Lieber CS. Alterations in endothelial fenestrations in liver sinusoids of baboons fed alcohol: a scanning electron microscopic study. Hepatology 4: 386–391, 1984.[Medline]
52. Matsumura T, Takesue M, Westerman KA, Okitsu T, Sakaguchi M, Fukazawa T, Totsugawa T, Noguchi H, Yamamoto S, Stolz DB, Tanaka N, Leboulch P, Kobayashi N. Establishment of an immortalized human-liver endothelial cell line with SV40T and hTERT. Transplantation 77: 1357–1365, 2004.[CrossRef][Medline]
53. Matsuura T, Kawada M, Hasumura S, Nagamori S, Obata T, Yamaguchi M, Hataba Y, Tanaka H, Shimizu H, Unemura Y, Nonaka K, Iwaki T, Kojima S, Aizaki H, Mizutani S, Ikenaga H. High density culture of immortalized liver endothelial cells in the radial-flow bioreactor in the development of an artificial liver. Int J Artif Organs 21: 229–234, 1998.[Medline]
54. Metchnikoff E. Lectures on the Comparative Pathology of Inflammation. London: Kegan Paul, Trench, Trubner, 1893. Reprinted in New York, NY: Dover Publications, 1968.
55. Meurer SK, Tihaa L, Lahme B, Gressner AM, Weiskirchen R. Identification of endoglin in rat hepatic stellate cells: new insights into transforming growth factor beta receptor signaling. J Biol Chem 280: 3078–3087, 2005.[Abstract/Free Full Text]
56. Mori T, Okanoue T, Sawa Y, Hori N, Ohta M, Kagawa K. Defenestration of the sinusoidal endothelial cell in a rat model of cirrhosis. Hepatology 17: 891–897, 1993.[CrossRef][Web of Science][Medline]
57. Mousa SA. Expression of adhesion molecules during cadmium hepatotoxicity. Life Sci 75: 93–105, 2004.[CrossRef][Medline]
58. Mouta Carreira C, Nasser SM, di Tomaso E, Padera TP, Boucher Y, Tomarev SI, Jain RK. LYVE-1 is not restricted to the lymph vessels: expression in normal liver blood sinusoids and down-regulation in human liver cancer and cirrhosis. Cancer Res 61: 8079–8084, 2001.[Abstract/Free Full Text]
59. Nachman RL, Jaffe EA. Subcellular platelet factor VIII antigen and von Willebrand factor. J Exp Med 141: 1101–1113, 1975.[Abstract/Free Full Text]
60. Nedredal GI, Elvevold KH, Ytrebo LM, Olsen R, Revhaug A, Smedsrod B. Liver sinusoidal endothelial cells represents an important blood clearance system in pigs. Comp Hepatol 2: 1, 2003.[CrossRef][Medline]
61. Ohi N, Nishikawa Y, Tokairin T, Yamamoto Y, Doi Y, Omori Y, Enomoto K. Maintenance of Bad phosphorylation prevents apoptosis of rat hepatic sinusoidal endothelial cells in vitro and in vivo. Am J Pathol 168: 1097–1106, 2006.[Abstract/Free Full Text]
62. Onoe T, Ohdan H, Tokita D, Shishida M, Tanaka Y, Hara H, Zhou W, Ishiyama K, Mitsuta H, Ide K, Asahara T. Liver sinusoidal endothelial cells tolerize T cells across MHC barriers in mice. J Immunol 175: 139–146, 2005.[Abstract/Free Full Text]
63. Pusztaszeri MP, Seelentag W, Bosman FT. Immunohistochemical expression of endothelial markers CD31, CD34, von Willebrand factor, and Fli-1 in normal human tissues. J Histochem Cytochem 54: 385–395, 2006.[Abstract/Free Full Text]
64. Rauen U, Hintz K, Hanssen M, Lauchart W, Becker HD, de Groot H. Injury to cultured liver endothelial cells during cold preservation: energy-dependent versus energy-deficiency injury. Transpl Int 6: 218–222, 1993.[CrossRef][Medline]
65. Sakurai F, Mizuguchi H, Yamaguchi T, Hayakawa T. Characterization of in vitro and in vivo gene transfer properties of adenovirus serotype 35 vector. Mol Ther 8: 813–821, 2003.[CrossRef][Medline]
66. Scoazec JY, Feldmann G. In situ immunophenotyping study of endothelial cells of the human hepatic sinusoid: results and functional implications. Hepatology 14: 789–797, 1991.[Web of Science][Medline]
67. Scoazec JY, Feldmann G. The cell adhesion molecules of hepatic sinusoidal endothelial cells. J Hepatol 20: 296–300, 1994.[CrossRef][Web of Science][Medline]
68. Shi J, Fujieda H, Kokubo Y, Wake K. Apoptosis of neutrophils and their elimination by Kupffer cells in rat liver. Hepatology 24: 1256–1263, 1996.[Web of Science][Medline]
69. Shiratori Y, Tananka M, Kawase T, Shiina S, Komatsu Y, Omata M. Quantification of sinusoidal cell function in vivo. Semin Liver Dis 13: 39–49, 1993.[Web of Science][Medline]
70. Smedsrod B. Clearance function of scavenger endothelial cells. Comp Hepatol 3, Suppl 1: S22, 2004.
71. Smedsrod B, Pertoft H, Eriksson S, Fraser JR, Laurent TC. Studies in vitro on the uptake and degradation of sodium hyaluronate in rat liver endothelial cells. Biochem J 223: 617–626, 1984.[Web of Science][Medline]
72. Smedsrod B, Tollersrud OK. Sinusoidal liver endothelial cells recruit lysosomal enzymes from the circulation by mannose-receptor mediated endocytosis. In: Cells of the Hepatic Sinusoid, edited by Wisse E, Knook DL, and Wake K. Leiden, The Netherlands: Kupffer Cell Foundation, 1995, p. 180–183.
73. Smedsrød B, Pertoft H, Gustafson S, Laurent TC. Scavenger functions of the liver endothelial cell. Biochem J 266: 313–327, 1990.[Web of Science][Medline]
74. Soilleux EJ, Morris LS, Rushbrook S, Lee B, Coleman N. Expression of human immunodeficiency virus (HIV)-binding lectin DC-SIGNR: consequences for HIV infection and immunity. Hum Pathol 33: 652–659, 2002.[CrossRef][Web of Science][Medline]
75. Steffan AM, Gendrault JL, McCuskey RS, McCuskey PA, Kirn A. Phagocytosis, an unrecognized property of murine endothelial liver cells. Hepatology 6: 830–836, 1986.[Web of Science][Medline]
76. Steffan AM, Lafon ME, Gendrault JL, Smedsrod B, Nonnenmacher H, Koehren F, Gut JP, de Monte M, Martin JP, Royer C, Kirn A. Productive infection of primary cultures of endothelial cells from the cat liver sinusoid with the feline immunodeficiency virus. Hepatology 23: 964–970, 1996.[CrossRef][Medline]
77. Tokairin T, Nishikawa Y, Doi Y, Watanabe H, Yoshioka T, Su M, Omori Y, Enomoto K. A highly specific isolation of rat sinusoidal endothelial cells by the immunomagnetic bead method using SE-1 monoclonal antibody. J Hepatol 36: 725–733, 2002.[CrossRef][Medline]
78. Tokita D, Shishida M, Ohdan H, Onoe T, Hara H, Tanaka Y, Ishiyama K, Mitsuta H, Ide K, Arihiro K, Asahara T. Liver sinusoidal endothelial cells that endocytose allogeneic cells suppress T cells with indirect allospecificity. J Immunol 177: 3615–3624, 2006.[Abstract/Free Full Text]
79. Ueno T, Inuzuka S, Tanikawa K. Changes of the extracellular matrix and cells producing it in acute liver injury. Gastroenterol Jpn28,Suppl 4: 107–111; discussion 112–105, 1993.
80. Urashima S, Tsutsumi M, Nakase K, Wang JS, Takada A. Studies on capillarization of the hepatic sinusoids in alcoholic liver disease. Alcohol Alcohol Suppl 1B: 77–84, 1993.
81. van der Kwast TH, Stel HV, Cristen E, Bertina RM, Veerman EC. Localization of factor VIII-procoagulant antigen: an immunohistological survey of the human body using monoclonal antibodies. Blood 67: 222–227, 1986.[Abstract/Free Full Text]
82. Van Furth R, Cohn ZA, Hirsch JG, Humprey JH, Spector WG, Langevoort HL. The mononuclear phagocyte system: a new classification of macrophages, monocytes and their precursor cells. Bull World Health Organ 46: 845–852, 1972.[Web of Science][Medline]
83. Volpes R, van den Oord JJ, Desmet VJ. Immunohistochemical study of adhesion molecules in liver inflammation. Hepatology 12: 59–65, 1990.[Web of Science][Medline]
84. Wion KL, Kelly D, Summerfield JA, Tuddenham EG, Lawn RM. Distribution of factor VIII mRNA and antigen in human liver and other tissues. Nature 317: 726–729, 1985.[CrossRef][Medline]
85. Wisse E. An ultrastructural characterization of the endothelial cell in the rat liver sinusoid under normal and various experimental conditions, as a contribution to the distinction between endothelial and Kupffer cells. J Ultrastruct Res 38: 528–562, 1972.[CrossRef][Medline]
86. Worgall S, Wolff G, Falck-Pedersen E, Crystal RG. Innate immune mechanisms dominate elimination of adenoviral vectors following in vivo administration. Hum Gene Ther 8: 37–44, 1997.[Web of Science][Medline]
87. Xu B, Broome U, Uzunel M, Nava S, Ge X, Kumagai-Braesch M, Hultenby K, Christensson B, Ericzon BG, Holgersson J, Sumitran-Holgersson S. Capillarization of hepatic sinusoid by liver endothelial cell-reactive autoantibodies in patients with cirrhosis and chronic hepatitis. Am J Pathol 163: 1275–1289, 2003.[Abstract/Free Full Text]
88. Yamasaki M, Ikeda K, Nakatani K, Yamamoto T, Kawai Y, Hirohashi K, Kinoshita H, Kaneda K. Phenotypical and morphological alterations to rat sinusoidal endothelial cells in arterialized livers after portal branch ligation. Arch Histol Cytol 62: 401–411, 1999.[CrossRef][Web of Science][Medline]
89. Yokomori H, Oda M, Yoshimura K, Nagai T, Ogi M, Nomura M, Ishii H. Vascular endothelial growth factor increases fenestral permeability in hepatic sinusoidal endothelial cells. Liver Int 23: 467–475, 2003.[CrossRef][Web of Science][Medline]
90. Zhang L, Dailey PJ, Gettie A, Blanchard J, Ho DD. The liver is a major organ for clearing simian immunodeficiency virus in rhesus monkeys. J Virol 76: 5271–5273, 2002.[Abstract/Free Full Text]
91. Zhang M, Gaschen B, Blay W, Foley B, Haigwood N, Kuiken C, Korber B. Tracking global patterns of N-linked glycosylation site variation in highly variable viral glycoproteins: HIV, SIV, and HCV envelopes and influenza hemagglutinin. Glycobiology 14: 1229–1246, 2004.[Abstract/Free Full Text]

This article has been cited by other articles:

				C. K. Seckert, A. Renzaho, H.-M. Tervo, C. Krause, P. Deegen, B. Kuhnapfel, M. J. Reddehase, and N. K. A. Grzimek Liver Sinusoidal Endothelial Cells Are a Site of Murine Cytomegalovirus Latency and Reactivation J. Virol., September 1, 2009; 83(17): 8869 - 8884. [Abstract] [Full Text] [PDF]

				S. C. Satchell and F. Braet Glomerular endothelial cell fenestrations: an integral component of the glomerular filtration barrier Am J Physiol Renal Physiol, May 1, 2009; 296(5): F947 - F956. [Abstract] [Full Text] [PDF]

				A. C. Straub, L. R. Klei, D. B. Stolz, and A. Barchowsky Arsenic Requires Sphingosine-1-Phosphate Type 1 Receptors to Induce Angiogenic Genes and Endothelial Cell Remodeling Am. J. Pathol., May 1, 2009; 174(5): 1949 - 1958. [Abstract] [Full Text] [PDF]

				V. C. Cogger, I. M. Arias, A. Warren, A. C. McMahon, D. L. Kiss, V. M. Avery, and D. G. Le Couteur The response of fenestrations, actin, and caveolin-1 to vascular endothelial growth factor in SK Hep1 cells Am J Physiol Gastrointest Liver Physiol, July 1, 2008; 295(1): G137 - G145. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: 294/2/G391    most recent 00167.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Elvevold, K. Articles by Martinez, I. Search for Related Content PubMed PubMed Citation Articles by Elvevold, K. Articles by Martinez, I.