Regulation of the Immune Response with Antigen Specific IgM Antibody: A Dual Role

Abstract IgM a-SRBC antibody administered before antigen produced an augmented response to a suboptimal dose of sheep erythrocytes (SRBC) in the mouse; however, this effect was not observed in two strains of rats tested. The same dose of IgM a-SRBC antibody which elicited an augmented response when given before the SRBC caused a significant suppression of the immune response when given 1 or 2 days after the SRBC. In vitro, IgM a-SRBC antibody suppressed the response of cultured mouse spleen cells to all doses of SRBC, whether given before or after immunization. In the intact mouse, IgM a-SRBC antibody apparently augments the primary immune response to low doses of antigen by increasing the number of SRBC localized in the spleen. Antibody must be present at the time of injection of the antigen for this effect to occur. However, IgM antibody can also act to suppress antibody-forming cells after antigen localization has occurred. Thus IgM antibody appears to play a dual role in the regulation of the immune response in the mouse.