Induction of T and B cell immunity by anti‐idiotypic antibody

Abstract A small dose of the IgG 1 fraction of anti‐idiotypic antibody (āId 1) raised in guinea pigs against a strain A/J antibody specific for streptococcal Group A carbohydrate sensitizes A/J mice against Group A streptococci. This is opposed to the previously established suppressive function of anti‐idiotypic antibody of the IgG 2 class (āId 2). Correspondingly, āId 1 but not āId 2 is eliminated from the circulation in the way typical of an immunogenic molecule. However, the stimulatory component in the IgG 1 fraction is not necessarily itself IgG 1 antibody. Sensitization occurs in both B and helper T lymphocytes and is specific for Group A streptococci. In the B cell compartment sensitization is restricted to precursor cells expressing the idiotype. The concomitant activation of T helper cells therefore suggests that these cells make use of receptors with a similar or identical idiotype. Efficient sensitization by āId 1 of both T and B cells is also demonstrated in strain C57L/J mice which upon immunization with Group A streptococci express a partially cross‐reacting idiotype as a minor component. When such animals were primed with āId 1, essentially all of the anti‐carbohydrate antibody carried the partially cross‐reacting idiotype.