ANTIGEN EXPRESSED BY SALMONELLA-TYPHIMURIUM IS PROCESSED FOR CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX PRESENTATION BY MACROPHAGES BUT NOT INFECTED EPITHELIAL-CELLS

Macrophages were shown to mediate class I major histocompatibility com plex (MHC-I) presentation of a fusion protein (Crl-OVA) expressed in S almonella typhimurium, a bacterium which fails to escape from vacuolar compartments after phagocytosis or penetration into host cells. Salmo nella typhimurium also penetrates into non-phagocytic intestinal epith elial cells, a portal of entry for systemic infection. We tested the a bility of infected epithelial cells to process antigen expressed by S. typhimurium for presentation by MHC-I molecules to CD8(+) T cells. CM T-93 murine adenocarcinoma cells expressed K-b and effectively present ed the OVA 257-264 peptide to CD8 OVA T-hybridoma cells, but infected CMT-93 cells failed to process Crl-OVA expressed in S. typhimurium. Th erapeutically useful MHC-I-restricted cytotoxic T-lymphocyte (CTL) res ponses may be generated by macrophage presentation of Salmonella antig ens or recombinant antigens expressed in Salmonella vaccine vectors. O ur data suggest that an inability of epithelial cells to present these antigens may limit the utility of CTL in epithelial immunity in salmo nellosis, but studies of additional epithelial cell systems are needed .