Prenatal Immunization of the Lamb to <i>Brucella</i>: Dissociation of Immunocompetence and Reactivity

Abstract

Abstract Many animal species do not respond markedly to the somatic antigens of Brucella or Salmonella until several weeks of age (1). Smith (2) found that only 1 of 58 human infants receiving typhoid vaccine at 1 to 30 days of age produced agglutinins against somatic antigen, although 46 of the 58 responded to the less complex flagella antigen. Passive transfer of antibody has been shown to inhibit immunization (3, 4), and maternal antibody may negate immune response in the neonate. Other evidence suggests that late maturation of immunocompetence is responsible for the non-reactivity toward the somatic antigens of Gram-negative bacteria. Silverstein and coworkers (5) have found that although the fetal lamb responded fully to several types of antigen at various times during fetal life, it did not produce antibody to Salmonella typhosa at any time in utero or by 6 weeks of age. Sterzl et al. (6) also were unable to detect antibody formation in fetal pigs injected with Brucella suis or Salmonella paratyphi. To resolve the question of late maturation versus non-reactivity, we have studied the antibody response of the fetal and neonatal lamb to Brucella antigens. The results clearly indicate that sheep are capable of responding to the antigenic stimulus at periods up to 70 days before birth, and that other factors are involved in the non-reactivity of newborn lambs toward the same antigen.