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1 Center for Basic Research in
Digestive Diseases,
Although the
clinical features of sclerosing cholangitis from opportunistic
infections of the biliary tree in patients with acquired
immunodeficiency syndrome (AIDS) are well known, the mechanisms by
which associated pathogens, such as Cryptosporidium parvum, cause disease are obscure. Using an in vitro
model of biliary cryptosporidiosis, we observed that
C. parvum induces apoptosis in
cultured human biliary epithelia. Both caspase protease inhibitors and
neutralizing antibodies to either Fas receptor (Fas) and Fas ligand
(FasL) inhibited this process; neutralizing antibodies to other
apoptotic cytokines [interleukin-1
(IL-1
), tumor necrosis
factor-
(TNF-
), and transforming growth factor-
(TGF-
)] had no effect. C. parvum stimulated FasL membrane surface translocation,
increased both FasL and Fas protein expression in infected biliary
epithelia, and induced a marked increase of soluble FasL (but not
IL-1
, TNF-
, and TGF-
) in supernatants from infected cells.
When a coculture model is used in which infected and uninfected cell
populations were physically separated by a semipermeable membrane, both
uninfected biliary epithelia and uninfected Fas-sensitive Jurkat cells
(but not a Fas-resistant Jurkat cell line) underwent apoptosis when
cocultured with infected biliary epithelia. Moreover, both a
neutralizing antibody to FasL and a metalloprotease inhibitor blocked
the apoptosis in uninfected cocultured cells. Activation of caspase
activity was also observed in uninfected cocultured biliary epithelia.
The data suggest that C. parvum
induces apoptosis in biliary epithelia by a Fas/FasL-dependent mechanism involving both autocrine and paracrine pathways. These observations may be relevant to both the pathogenesis and therapy of
the cholangitis seen in AIDS patients with biliary cryptosporidiosis.
acquired immunodeficiency syndrome; cholangiopathies; opportunistic infections; parasitic diseases; caspase
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