Abstract
Three antigenically distinct immunoglobulins of the IgG type, denoted as γ2, γ1 and γGs, have been previously identified in bovine serum. Forty to 50% of the serum IgG is composed of the γGs fraction, which was found to be the only important protein component of the colostrum.
Cattle given several courses of immunization with rabbit serum albumin or egg albumin in incomplete Freund's adjuvant have a remarkable immune response. As a consequence of immunization, important changes were observed in the concentration of antibodies associated with the different classes of IgG immunoglobulins. By comparing the antibody activities of these fractions after the first and the third courses of immunization, the increase of γ2 type antibody was found to be much more pronounced than that of the γGs class antibodies. This gradual quantitative shift of activity from γGs to γ2 immunoglobulin accompanied and was apparently responsible for a similar change in the association rates of the different classes of IgG globulins. During the immunization period there was a transition from low to high speed association of antibodies belonging to the γ2 type. Simultaneously, a progressive decrease in the association rates of γGs class antibodies was found after several courses of immunization. The reason for variability in the association rate of the different IgG classes of antibodies during the course of immune response is discussed.
