EFFECTS OF IGM ALLOTYPE SUPPRESSION ON SERUM IGM LEVELS, B-1 AND B-2 CELLS, AND ANTIBODY-RESPONSES IN ALLOTYPE HETEROZYGOUS F1-MICE

IgM allotype heterozygous F1 mice were independently suppressed for Ig h6a or Igh6b to evaluate the contribution of B-1 and B-2 cells to natu ral serum IgM levels and Ab responses. B-2 B cells expressing IgM of t he suppressed allotype were evident in the spleens of suppressed mice 4 to 6 weeks after cessation of the suppression regimen, whereas B-1 B cells of the suppressed allotype were undetectable for up to 9 months . Although serum IgM of the suppressed allotype was initially depleted in mice suppressed for either allotype, by 7 months of age, there wer e detectable levels of IgM of the suppressed allotype in the serum; ho wever, the levels were significantly below that found in nonsuppressed mice. When mice were immunized with either the T-independent or T-dep endent form of phosphorylcholine, those suppressed for either allotype , and consequently depleted of B-1 B cells of that allotype, did not r espond with phosphorylcholine-specific IgM of the suppressed allotype. In contrast, when mice were immunized with alpha 1-3 dextran, the Igh 6a allotype-suppressed mice were able to produce dextran-specific IgM of that allotype. These results show that allotype-bearing B-1 cells o f both allotypes can be effectively suppressed by this suppression pro tocol and this produces long-lasting effects on B-1 cell levels and se rum IgM of the suppressed allotype. These observations reflect the der ivation of the majority of B-1 cells from fetal-neonatal precursors, w hich cannot be replaced by newly emerging B-2 cells of adult origin. T heir ablation by antibody treatment results in permanent alterations t o the adult B-cell repertoire.