The effect of antigen dose on the kinetics of circulating antibody synthesis and on antibody affinity was studied in a haptenic system. High doses of antigen resulted, early in immunization, in higher concentrations of antibody followed later in the immune response by decreased serum levels of antibody as compared with lower doses of antigen. The affinity of the initial antibody synthesized was very similar over a wide antigen dose range. Subsequently, however, a rapid rise in affinity was seen in animals immunized with low doses of antigen, while relatively little change in affinity was seen in animals immunized with higher antigen doses. Suppression of active antibody formation by passive antiserum led to an increase in antibody affinity.
The results are discussed in terms of the mechanisms involved in the selection of a population of cells to participate in the immune response and the mechanisms whereby antigen dose and circulating antibody function to control antibody synthesis.