Immunity to Salmonella gallinarum during ontogeny of the chicken: III. Bactericidal antibody

The bactericidal activity of chicken serum before and after injection of 1–35-day-old chickens with Salmonella gallinarum has been studied. The bactericidal action of immune serum is temperature-dependent. Treatment of both normal and immune serum with mercaptoethanol, by heating to 56°, produced a ten-fold reduction in bactericidal activity. The ingested yolk contained bactericidal factors at 1 day of age. Bactericidal activity of normal serum declined very slowly during the first 5 weeks of development. Bactericidal activity released by injection of S. gallinarum, showed some specificity for the somatic-O antigens and a high degree of species specificity. Injection of S. gallinarum into 1-day-old chicks resulted in the rapid release of a high level of bactericidal activity into the circulation. The bactericidal antibody response to an injection of S. gallinarum increased from 4 to 35 days of development. In chickens of 3 weeks of age, or older, induced bactericidal antibody remained at a high level for several weeks.