The immune response to bacterial dextrans. I. Genetic control of responsiveness.

The in vivo antibody response to the thymus-independent (TI) antigen dextran B512 (Dex) was studied in various mouse strains. We found no non-responder strains but rather that the magnitude of Dex-specific plaque-forming cell and serum antibody responses varied markedly among individual mice, even if these were of the same age and litter and kept in the same environment. This was the case both for mouse strains previously described genetically as high (IgCHb,j) and for those described as low (IgCHa) responders to Dex [14]. In 'low'-responder BALB/c mice, the responsiveness to Dex increased with age, such that a large fraction of these mice responded as well as 'high'-responder C57BL/6 mice. Analysis of aged back-cross populations derived from IgCHb and IgCHa parental strains further substantiated these findings. Thus, all backcross mice, irrespective of IgCH haplotype, responded on the average equally well to Dex. According to our studies, therefore, the assignation of high or low responsiveness to IgCH locus-linked genes cannot be done unequivocally.