Effects of antigen-feeding on intestinal and systemic immune responses. IV. Similarity between the suppressor factor in mice after erythrocyte-lysate injection and erythrocyte feeding.

Profound antigen-specific suppression of humoral antibody responses to subsequent antigen challenge can occur in mice after oral antigen administration. We previously demonstrated that suppression of antibody responses in mice fed heterologous erythrocytes was mediated by a serum suppressor factor. This soluble factor markedly inhibited anti-erythrocyte antibody responses after erythrocyte challenge in vivo or in vitro. We now demonstrate a suppressor factor in the serum of mice injected parenterally with an erythrocyte lysate that is indistinguishable by several criteria from the suppressor factor in the serum of erythrocyte-fed mice. The suppressor factor in both erythrocyte lysate-injected and erythrocyte-fed mice has a mol wt of 150,000 daltons, is heat stable, contains Ig determinants, and lacks detectable erythrocyte determinants. Suppression mediated by both factors is antigen-specific, not H-2 restricted, and inhibits IgM responses to a greater extent than IgA or IgG responses. These findings indicate that the production of serum suppressor factors like those seen after antigen-feeding does not require enteric antigen exposure.