Inhibition of immunological components by antigenic competition and other immuno-depressing procedures.

Four experimental procedures leading to lower antibody production, namely administration of a minute amount of antigen or excess of antigen, competition with an unrelated antigen and treatment with methotrexate, were studied for their effect on each of the forms of immunological responses in guinea-pigs to a DNP-BSA conjugate. It was found that delayed hypersensitivity and 2-ME sensitive antibody production were more reduced by administration of excess of antigen or by competition than by giving a minute amount of antigen or methotrexate. On the other hand, IgG1 production was more suppressed in the groups receiving minute amounts of antigen or methotrexate treatment than in those given excess of antigen or subjected to competition. IgG2 production was markedly reduced in all four groups of animals. However, excess of antigen and competition changed the kinetics of both total antibody and IgG antibody production (peak on day 20 after immunization). The peak of total as well as IgG2 antibody-production in the groups given a minute amount of antigen or methotrexate, was on day 35, the same as in optimally immunized animals. These results suggest that a common mechanism for reduction of the immune response may be responsible for the excess of antigen and competition effects on one hand and the minute amount of antigen and methotrexate effects on the other. Competition with an unrelated antigen and excess of the same antigen could both act on the same effector cell. Methotrexate could act not only by killing a proportion of immunologically competent cells, but also by lowering their sensitivity to stimulation by antigen.