MAST-CELLS PROCESS BACTERIAL AGS THROUGH A PHAGOCYTIC ROUTE FOR CLASS-I MHC PRESENTATION TO T-CELLS

The pivotal role of mast cells in allergic reactions and inflammatory processes is well established and recent studies have suggested that m ast cells may also have a role in specific immune responses, Because m ast cells have been shown to phagocytose and kill enterobacteria, we w ished to determine whether they could also process bacterial Ags for p resentation to T cells, Using a model system in which a well-character ized T cell epitope is expressed within bacteria as a fusion protein, we demonstrate in this paper that mast cells are indeed capable of pro cessing bacterial Ags for presentation through class I MHC molecules t o T cell hybridomas after phagocytic uptake of live bacteria, Processi ng occurs from a number of Gram-negative enterobacteria including Salm onella typhimurium and Escherichia coli, Parallel assays show that pro cessing of the model Ag from enterobacteria by mast cells is similar i n efficiency to processing by peritoneal macrophages. Consistent with earlier observations demonstrating a function of the bacterial fimbria l protein FimH in promoting bacterial binding to mast cells, the magni tude of the Ag processing response of E. coli is influenced by bacteri al expression of FimH, Taken together, these observations extend the r ange of cell types capable of the phagocytic pathway of Ag processing and suggest that mast cells may have a previously unrecognized role in the induction of specific immune responses to bacteria.