Protective immunity induced by porin against Salmonella infection in mice

Porin, a major outer membrane protein was purified from Salmonella typhimurium and its immune potential was studied in mice. Active immunization with porin induced about 45 per cent protection to an intravenous challenge with 10LD50 of S. typhimurium. Further, in porin immunized mice significant level of anti-porin antibodies and DTH reaction were detected. Attempts were also made to improve the immune potential of porin. Freund's complete adjuvant when mixed with immunogenic doses of porin enhanced the anti-porin antibody titre. However, it could not improve the protective ability of porin. On the other hand, porin when injected along with lipopolysaccharide (LPS) induced a higher level (55% survival with 50LD50) of protection than porin or LPS alone. This finding was also substantiated by the significantly reduced in vivo growth of challenge organisms in mice immunized with porin plus LPS. These results indicate that porin is a protective antigen and LPS significantly enhances the protective ability of porin.