Differential and mutually exclusive expression of CD95 and CD95 ligand in epithelia of normal pancreas and chronic pancreatitis

Acinar regression in chronic pancreatitis may be due to immune attack in parenchymal areas neoexpressing HLA-DR molecules. CD4⁺Th1 cytotoxic T cells induce apoptosis of their targets via oligomerizing CD95 (APO-1/Fas) death receptors on target cells by their CD95 ligand (CD95L). We determined the expression of CD95 and CD95L in epithelia of normal and chronically inflamed pancreatic tissues. We applied RT-PCR and Western blotting for CD95L expression profiles, serial frozen section immunohistochemistry to detect CD95, CD95L, and HLA-DR molecules, CD3, CD4, CD11c, and S-100 protein (S100p). Normal pancreases and chronic pancreatitis contain CD95L message and protein. Immunohistochemistry revealed a mutually exclusive expression of CD95 and CD95L. Physiologically, acini were CD95^-/CD95L⁺, ducts were CD95^-/CD95L^-, and islets were CD95^-/CD95L⁺. In areas of lymphohistiocytic infiltration, mainly consisting of CD3⁺CD4⁺ T cells and CD11c⁺, CD4^+/-, S100p⁺ interstitial dendritic cells, and in areas of initial fibrosis, acini and ducts were HLA-DR⁺, acini CD95⁺/CD95L^-, and ducts CD95⁺/CD95L^-. Islet cells were CD95^-/CD95L⁺ in both conditions. IFNγ, levels in protein lysates, as measured by an immunoassay, were significantly higher in chronic pancreatitis than in normal pancreas (p < 0.0003). In vitro, IFNγ, down-modulated CD95L message and protein in ASPC1 and BxPc3 pancreatic carcinoma cells. In conclusion, pancreatic epithelia differentially express CD95 and CD95L in a mutually exclusive manner. In chronic pancreatitis the CD95^-/CD95L⁺ status is conserved in islet cells even in the vicinity of lymphohistiocytic infiltrates, whereas it is lost in acini coexpressing HLA-DR. As a potential consequence, and possibly triggered by local release of IFNγ, CD4⁺Th1 cells may cognately interact with and successfully attack exocrine cells by triggering CD95 on their target without being killed by epithelial, CD95L-mediated, counterattack.