The number of antibody-producing clones as revealed by the distribution of allelic variants of immunoglobulin light chains.

A new method of evaluation of the number of clonal precursors of antibody-producing cells based on the phenomenon of allelic exclusion is proposed. The distribution of the allotypes of specific antibodies in the population of heterozygous F1 hybrids depends on the number of clonal precursor cells. The smaller the number of precursors, the larger the variance of the distribution. The frequency of clones producing antibodies to the azobenzoate hapten (approximately 10(-8) after first and approximately 10(-9) after second and third immunizations) in (MSU X August)F1 rats calculated in the present work is in reasonable agreement with the data obtained (for other haptens) by limiting dilution cloning assays. The difference in the numbers of anti-hapten and anti-carrier clones is discussed. The numbers of IgM and IgG-synthesizing clones are calculated from the distributions of the allelic variants of corresponding rat antibodies to lactoside. The data suggest the existence of distinct IgG precursors which contradicts the hypothesis of IgM-IgG switch within the clones only.