Role of immunoglobulin and peritoneal phagocytes in the protection of rats against salmonella infection.

Intradermal vaccination of rats with heat-killed Salmonella dublin protected against an intraperitoneal challenge of live S dublin. Serum from vaccinated animals administered intraperitoneally protected normal rats against intraperitoneal challenge with S dublin and four other serotypes. Protection was attributed to opsonic antibodies which promoted phagocytosis by mononuclear phagocytes. The opsonin was identified as IgG2a which prevented lysis of macrophages and enabled them to contain the pathogen at the site of infection. In vitro, mononuclear phagocytes killed S dublin for up to two hours after phagocytosis in the presence of immune rat serum.