Relative Concentrations of IgM and IgG Antibodies during the Primary Response

Abstract

The synthesis of IgM and IgG antibodies to bovine serum albumin was examined during the primary response in the rabbit. After separation of the two immunoglobulins by gel filtration or density gradient ultracentrifugation, the quantity of antibody was determined by a modified antigen-binding procedure. The assay allowed weight estimates of the antibody concentration to be made, was dependent only on the primary union of antigen with antibody and did not demonstrate a selective efficiency in detecting one immunoglobulin class of antibody over the other. IgM and IgG antibodies initially appeared in the serum at approximately the same time. At the peak of the primary response IgG antibody was present in a 50-fold molar excess over IgM. Active synthesis of IgM antibody took place in the presence of this large excess of IgG antibody. These observations do not support an inhibitory role of IgG antibodies on IgM synthesis. During the study it was determined that the intact IgM antibody molecule bound a maximum of five to six antigen molecules when measured by the modified antigen-binding procedure.