Protective immunity and the cell-mediated immune response in mice following oral administration of an avirulent strain of Salmonella typhimurium.

Oral vaccination with Salmonella typhi-murium M 206 has been shown to confer highly significant protection on BALB/c and low-responder (LR) Biozzi mice a 30 days, but no protection was observed in high-responder (HR) Biozzi mice. None of the three strains showed any evidence of significant protection 10 days after primary vaccination. A correlation was noted between the degree of protection and the results of tests measuring cell-mediated immunity, both in vitro (MIF test), and in vivo (colloidal carbon clearance). Phagocytosis was significantly more active in vaccinated mice, both at days 10 and 30, except in HR mice. MIF production was only found at day 10 in HR mice, and was present at day 30 in both HR and LR mice. Our results emphasize the importance of the role of macrophage phagocytosis in the protection of mice against Salmonella infections.