Effect of Antibody on Antibody Synthesis

I t has long been recognized that preexisting antibody, either endogenously formed, or passively administered near the time of the injection of the corresponding antigen, can affect the subsequent antibody response. An excess or, in some cases, even an equivalent amount of passively administered antibody can partially or completely inhibit the primary response in a previously unchallenged animal (1-12) and passively administered or previously synthesized antibody may, under certain conditions, diminish the response to a secondary challenge (10, 13-15). On the other hand, with certain antigens, relatively small amounts of passively administered antibody actually may enhance the antibody response (12, 16-18). The mechanism by which preexisting or passively transferred antibody suppresses the antibody response is not entirely clear. I t could be either by covering the immunogenic sites of the antigen and thereby preventing or diminishing the immunogenic stimulus, or by a direct suppressive action on the cells destined to respond to the antigen. In the broad sense, either of these actions might be considered a "feedback mechanism" since the product of the response, antibody, would serve, directly or indirectly, to prevent or diminish the response. Most of the available observations of this phenomenon are based on experiments which utilize complex antigens and at least equivalent or, more often, large excesses of antibody in relation to the immunogenic challenge and are, therefore, of little help in choosing between these two possibilities (8-14). Those experiments designed to eliminate the excess antibody by exposing potentially immunocompetent cells to passive antibody prior to or during transfer to unresponsive hosts have led to conflicting results (10, 11).