Stimulation and inhibition of macrophages prior to immunization with a hapten-carrier conjugate.

Delayed hypersensitivity reactions and antibody-mediated reactions to the carrier and to the hapten have been studied in animals treated with BCG or/and trypan blue before immunization with a hapten-carrier complex. The results show that it is possible to induce, with BCG, at the beginning of the response, an antigenic competition between hapten and carrier moieties of the antigen molecule. Macrophages which modulate the response to the hapten-carrier complex by acting both on T cells involved in cellular immunity and those involved in antibody synthesis, appear to be the target of antigenic competition.