Recombinant Rabbit Secretory Immunoglobulin Molecules: Alpha Chains with Maternal (Paternal) Variable-Region Allotypes and Paternal (Maternal) Constant-Region Allotypes

A population of IgA molecules having heavy chains coded by two parental chromosomes in trans position has been identified in rabbits heterozygous at both the VHa locus, which controls allotypic specificities on the variable part of heavy chains, and the Cαg locus, which controls allotypic specificities on the constant part of alpha chains. These recombinant molecules have alphachain allotypic specificities controlled by both the maternal VHa gene and the paternal Cαg gene or conversely, the paternal VHa gene and the maternal Cαg gene. These recombinant molecules were found in F(ab)2αfractions obtained after passage of F(ab)2αpreparations through immunosorbent columns designed to remove one population of F(ab)2αmolecules, i.e., g74- or g75-type molecules. The effluent F(ab)2αfractions were then examined by radio-precipitation methods for allotypic specificities controlled by the VHa and Cαg loci. About 40% of the g75 F(ab)2αmolecules from each of three rabbits with the a1g74and a2g75allogroups were alg75 recombinants. These alg75 recombinant molecules represented from 2.5-5.6% of the total unfractionated F(ab)2αsample. The F(ab)2αfractions from two rabbits with the a1g75and a3g74allogroups had from 1.8-8.2% recombinant molecules: some were alg74 recombinants and some were a3g75 recombinants. Somatic recombination as a mechanism responsible for the synthesis of polypeptide chains in which part of the information is obtained from one chromosome and part from the homologous chromosome is discussed.