Antibody-Mediated Suppression of the Immune Response: Effect on the Development of Immunologic Memory

Abstract

The nature of the immune response to a second injection of sheep red blood cells (SRBC) following a primary immune response suppressed by passive antibody was investigated in C57BL/Ks mice. Mice received a primary injection of SRBC and homologous anti-SRBC serum; 2, 4, 6 and 8 weeks later groups of mice were challenged with SRBC. The immune response was evaluated by determining the number of cells synthesizing 19S or 7S anti-SRBC in the spleens. A quantitatively low response which qualitatively resembled a secondary immune response was observed when mice were challenged with SRBC 2 weeks after the primary immune response had been suppressed by passive antibody. This response could not be duplicated in normal mice by priming with lower doses of antigen, suggesting that simple antigen clearance is not the sole mechanism in antibody-mediated suppression of the primary immune response. Increasing the interval up to 8 weeks between the suppressed primary response and the second challenge of antigen resulted in responses which approached those observed in the secondary response of normal mice. The possibility that antibody might prevent full expression of the secondary immune response was studied by testing the response in the antibody-free environment of a cell culture system. The immunologic responsiveness of spleen cells from normal mice, from mice injected with anti-SRBC, from mice primed with SRBC only, and from mice given anti-SRBC and SRBC was examined in cell culture. Spleen cells obtained from normal mice and from passively immunized mice responded with equal in vitro primary responses to SRBC, showing that the suppressive effects of antibody can be washed from the cells. Spleen cells obtained from passive antibody-suppressed mice produced a secondary response in vitro equal to that seen in cell cultures prepared from primed spleen cells. These results show that although passive antibody suppressed the synthesis of antibody during the primary response, priming for a secondary immune response was not inhibited.