Regulation of the Immune Response

The ability of 7S and F(ab')(2) antibody fragments to suppress priming with low doses of antigen was compared. The 7S preparation was approximately 100-1000 times more potent than the F(ab')(2) preparation when the agglutinin titers of the two preparations were the same. The presence of any ability to suppress priming in the F(ab')(2) preparation may reflect an inherent capacity of the F(ab')(2) antibody or contamination with small amounts of 7S antibody. The difference between 7S and F(ab')(2) antibody in ability to suppress priming is attributed to the lack of the Fc portion on the F(ab')(2) antibody. The Fc portion may be needed to prevent rapid excretion of antibody from the body, to induce rapid phagocytosis of antigen-antibody complexes with consequent breakdown and elimination of antigen, or to inactivate or suppress the antigen-sensitive cells from reacting to antigenic determinants. More detailed studies will permit a better assessment of the importance of these three possible regulatory roles of the Fc portion of the immunoglobulin in the immune response.