Expression of cathepsins B, L, S, and D by gastric epithelial cells implicates them as antigen presenting cells in local immune responses

Helicobacter pylori infection is linked to chronic gastritis, peptic ulcer and gastric carcinoma. During H. pylori infection, class II MHC expression by the gastric epithelium increases, as does the number of local CD4(+) T c ells, which appear to be important in the associated pathogenesis. These ob servations suggested that the epithelium might present antigens to T cells. Thus, we sought to determine whether gastric epithelial cells process anti gens to establish their function as local antigen presenting cells (APC). W e examined a panel of gastric epithelial cell lines for expression of the a ntigen processing cathepsins B (CB), L (CL), S (CS), and D (CD). The mRNA f or these enzymes were detected by RT-PCR and the enzymes in the gastric epi thelial cells were identified by various independent methods. We corroborat ed the expression of CB and CD on gastric epithelial cells from human biops y samples, The functions of these proteases were confirmed by assessing the ir ability to digest ovalbumin, a conventional dietary antigen, and protein s from H. pylori. In summary, multiple lines of evidence suggest gastric ep ithelial cells process antigens for presentation to CD4(+) T cells. To our knowledge, these are the first studies to document the antigen processing c apacity of human gastric epithelial cells, (C) American Society for Histoco mpatibility and Immunogenetics, 2001. Published by Elsevier Science Inc.