The immune response of nine inbred and one outbred strain of mice to the streptococcal group A polysaccharide was investigated with respect to magnitude and restriction. Analytical isoelectric focusing served as a tool to estimate the degree of restriction of Group A polysaccharide-specific antibodies.

It proved feasible to distinguish low and intermediate from high responder strains, and to delineate strain-specificity of isoelectric focusing spectra of the immune sera. For example, immune sera of BALB/c mice, restricted high responders, and of C57BL/6 mice, heterogeneous low responders, had distinct focusing properties.

Responsiveness was a dominant autosomal genetic trait in C57BL/6 x BALB/c F1 hybrid mice, irrespective of the maternal and the paternal genotype; the immune sera of these mice had their own, rather uniform isoelectric focusing spectra whereby structural genes of the low responder strain were expressed to predominant levels in 81% of the hybrids.

Responsiveness in C57BL/6 x BALB/c F2 progeny segregated into 79% high and 21% low responders, and showed no genetic linkage to the following characteristics: hair color, sex, H-2 type, and Ig allotype of the heavy chain. The isoelectric focusing properties of these immune sera indicated segregation into patterns like BALB/c mice (40%), F1 hybrids (48%), and C57BL/6 mice (12%). Since this segregation is independent of any of the above criteria in these F2 mice a regulatory gene(s) is postulated that controls the clonal pattern of the immune response.

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