The correlation between serum IgA antibody levels and resistance to infection with Salmonella typhimurium after oral immunization with various salmonellae.

Subsequent to oral feeding of various Salmonella strains to mice, the IgA antibodies directed against the O-somatic antigens of the immunising strain were measured in both serum and intestinal juice, using the ELISA technique. 21 days after oral immunization the IgA antibody levels were relatively high only in those mice which were resistant to challenge with a virulent strain of Salmonella typhimurium. Because there was no correlation between protection and the specificity of the 'O' somatic antigens of the immunising and challenge strains, the IgA antibodies measured were not responsible for protection. Nevertheless, the level of these antibodies affords a good index of the resistance of mice or immune status of mice to Salmonella infection.