Differences in the genetic control of primary and secondary antibody responses.

Primary and secondary antibody responses to f and s antigens of Salmonella typhimurium have been studied in H and L lines of mice genetically selected for primary reponse to sheep erythrocytes (SE) (Selection I). The range of interline separation obtained (non-specific effect of Selection I) was as large as for the selection antigen in the primary response to f antigen and slightly smaller in the primary response to s antigen. For these two antigens the interline difference was reduced after booster. The kinetics of responses were compared with those obtained in H and L lines of Selections III and IV carried out for secondary responses to f and s antigens of S. typhimurium respectively (specific effect of Selection III and IV). The genetic analysis was made in Selection I from the variances of individual agglutinin titres obtained in large groups of interline hybrids immunized with S. typhimurium. These calculations gave a reliable estimate of the effective number of independent loci regulating primary and secondary responses. The results demonstrated a major difference in the genetic control: a single locus regulated the secondary response to f antigen while six loci were involved in the control of the primary response. A similar difference was evident for s antigen. The primary response was likely to be under polygenic regulation although the effective number of loci could not be calculated, while the secondary response was under monogenic control.