Mechanisms involved in the antibody-mediated suppression of tuberculin-type delayed hypersensitivity: the effects of antigen concentration on tolerance induction, the ability of antigen-antibody complexes to render tolerant and the effects of toleration on antigen-induced in vitro proliferation.

Long-lived tuberculin-type delayed hypersensitivity to chicken conalbumin (CA), as measured by skin-reaction, is inhibited in CAF1 mice by passively administered hyperimmune mouse antiserum to CA. We describe here three new parameters of this inhibition: (1) induction of tolerance is not dependent on the concentration of antigen used to sensitize, even when 3.6-fold more antigen is administered than the tolerizing antibodies can bind; (2) antigen-antibody complexes formed in vitro can inhibit; and (3) although induction rather than reaction is suppressed by antiserum treatment, early stages of sensitization are not inhibited. This is shown by the capacity of inguinal lymph node cells from suppressed mice to proliferate in vitro, in response to antigen, 7 and 14 days after sensitization and antiserum treatment. In fact, this in vitro proliferative response is specifically enhanced in suppressed mice on day 7. These results suggest a complex mechanism of antibody-mediated immunoregulation.