Genetic parameters of the polygenic regulation of antibody responsiveness to flagellar and somatic antigens of salmonellae

Selective breedings of mice were carried out for quantitative antibody responsiveness to flagellar Ag., f (Selection III) or somatic Ag., s (Selection IV) of two non cross-reacting Salmonellae (Salm. tm., Salm. or.) alternated for immunization of consecutive generations. At the selection limit, these selections produced homozygous high (H) and low (L) responder lines for the character investigated: peak agglutinin response to optimal secondary immunization. The responsiveness to both f and s Ags. is submitted to polygenic regulation. The heritability (h2) realized during the selective breeding was 0.37 +/- 0.07 for the response to fAg. and 0.40 +/- 0.1 for the response to s Ag. The respective part of genetic and environmental variance in F2 hybrids was 64% and 36% in selection III and 61% and 39% in selection IV. In the two selections, the dominance variance is negligible (less than 1%), therefore the genetic variance is essentially additive. The additive variance calculated as the heritable fraction of the F2 hybrid variance is somewhat lower, the reason for this difference is discussed. The quantitative antibody response to f Ag. in selection III is controlled by about seven independent loci. The antibody response to s Ag. in selection IV is controlled by about four independent loci. A possible association of relevant genes with the H-2 locus was investigated. In selection III, no significant participation if H-2 linked genes, in the regulation of responses to f and s Ags. of Salm. tm and Salm. or. could be demonstrated. In selection IV a partial contribution of H-2 linked genes was observed concerning responsiveness to both f and s Ags. of Salm. tm. but not Salm. or. Ags. The H-2 effect accounts for 25% of the total interline difference.