Infection and Reinfection of Chickens with Salmonella typhimurium: Bacteriology and Immune Responses

The Spc' mutant stimulated strong IgG, IgA, and IgM responses in serum, small-intestinal contents, and bile. These were detected by enzyme-linked immunosorbent assay (ELISA) against antigens of crude whole bacterial cell protein sonicate, lipopolysaccharide, flagella, and outer-membrane proteins. There was some evidence of an anamnestic response with IgA in bile following reinfection with the Salmonella. The peak response of antibody-producing cells from the spleens of infected chickens, assayed by solid-phase ELISA, occurred at 3 weeks postinoculation. A strong delayed hypersensitivity reaction, detected by foot-pad swelling after inoculation with either whole-cell or outer-membrane proteins, was observed between 2 and 5 weeks after infection with the Spc' mutant. The data indicate that outer-membrane proteins are major immunogens for both humoral and cell-mediated arms of the immune system.