Expression of a mouse immunoglobulin V gene in homozygote and heterozygotes.

Our earlier work had demonstrated a fine-specificity idiotype in anti-NP antibodies of C57Bl/6 mice. It was controlled by a VH gene (VH-NPb). The idiotype could be demonstrated in all anti-NP of the C50Bl/6 mice (IgG, IgA, IgM including natural anti-NP). The VH-NPb gene is condominant with CBA allele F1 hybrid mice in the production of natural antibodies but dominant over the CBA allele in immune antibody formation (92% of F1 mice were like C57Bl/6). Probably the product of this gene has a higher affinity for NP than the average affinity of idiotype-negative antibody in the F1 hybrids. Both the codominance in natural antibodies and the dominance in immune antibodies had the peculiar characteristic that genotypically identical individuals varied a great deal. The share of idiotype-positive antibody in the total natural anti-NP titre of (C57Bl/6 x CBA)F1 mice varied from less than 33% to more than 67%. In immune antibodies individual differences were still greater, in ca 92% of mice only idiotype-positive anti-NP could be detected and in ca 8% only idiotype-negative antibody was detectable. Only few F1 hybrid mice had detectable amounts of both types. Homozygous mice of the LP strain behaved in all aspects like the F1 mice. Of their natural anti-NP titres 50% were due to idiotype-positive antibody and in the immune antibodies the figure was 86%. Individual non-immune sera again contained varying mixtures of idiotype-positive and idiotype-negative antibody, but immune sera contained only one or the other type. The third allotype b strain tested, C57Bl/Ka, took an intermediary position between LP and C57Bl/6. Ca 70% of natural anti-NP titres were due to idiotype-positive antibody but all immune anti-NP was idiotype-positive.