MACROPHAGE-T CELL-INTERACTION IN MURINE SALMONELLOSIS - SELECTIVE DOWN-REGULATION OF ICAM-1 AND B7 MOLECULES IN INFECTED MACROPHAGES AND ITS PROBABLE ROLE IN CELL-MEDIATED-IMMUNITY

Vaccine development and understanding of cellular immune modulatory me chanisms in salmonella infections have been impeded due to the paucity of data on antigens capable of eliciting effective immune responses. The present study was done to evaluate the efficacy of five major puri fied salmonella antigens (porins, pili, flagella, outer membrane prote ins and heat shock proteins) in modulating T cell-macrophage interacti ons which play a central role in resistance to and recovery from infec tion with several intracellular pathogens, including salmonella. The r esults showed that the T cells recovered 10 days post-immunization (D- 10 T cells) from mice immunized with porins and outer membrane protein s showed maximum proliferation in the presence of macrophages incubate d with dead bacteria; however, this response was decreased when T cell s were co-cultured with live Salmonella typhimurium-infected macrophag es. Delayed-type hypersensitivity responses, as measured by increased footpad thickness at 24 h, though induced effectively by porins, pili and flagella, were completely abrogated when D-10 T cells were pre-inc ubated with macrophages infected with live bacteria. The phagocytic an d bactericidal ability of normal macrophages, when grown in presence o f T cel supernatants, was not influenced by the immunizing agents, but T cell supernatants obtained from mice immunized with porins and heat -shock protein triggered increased bactericidal activity. Further, the expression of the co-stimulatory molecules ICAM-1 and B7 increased wi th increasing bacteria (dead):macrophage ratio, but this expression wa s down-regulated upon incubation with live bacteria.