Immunization of rabbits from a closed colony with streptococcal Group A-variant vaccines identified about two-thirds of them as low and heterogeneous responders. One-third of the rabbits showed a restriction of the response independent from the magnitude. Selective breeding from one monoclonal high-responder male and two restricted high-responder female rabbits succeeded in segregation of high-responder progeny after two generations. Their antibody levels were on the average 2.5 times higher than those of the random group of rabbits and a small group of low-responder offspring.
Immunization of 13 offspring originating from rabbits bred for restricted high response to the streptococcal Group C polysaccharide revealed that 11 progeny were restricted high responders and 2 progeny monoclonal high responders. This finding suggests that high responsiveness to the Groups A-variant and C polysaccharides is inherited as genetically linked traits.
Selective breeding combinations between restricted and monoclonal high-responder rabbits by brother-sister matings succeeded in narrowing the isoelectric focusing spectra of Group A-variant-specific antibodies in the offspring. It furthermore revealed a preferential expression of monoclonal antibodies after three generations with a similar net charge as those identified first in the original monoclonal paternal parent. These data suggest that similar copies of structural genes for the variable regions are transmitted from the parent to the progeny.