Distribution of Allotypic Specificities A1, A2, A14, and A15 Among Immunoglobulin G Molecules

Abstract

The distribution of specificities A1, A2 (Fd-associated allotypes of rabbit heavy chains), A14 and A15 (Fc-associated allotypes of rabbit γ chains) was studied using ¹²⁵I-labeled IgG from homozygous and heterozygous rabbits of known pedigree. The IgG of an A1, 14/A2, 15 rabbit whose pedigree showed that A1 was genetically associated with A14 had closely similar proportions of these two specificities (80%), whereas IgG of an A1, 15/A2, 14 rabbit with A2 in coupling with A14 had equal proportions of these two specificities (20%). A rabbit with suppressed phenotypic expression of the A1 allotype was also suppressed for the A14 to which it was coupled. The quantitative expression of the Fc allotype (A14 or A15) is influenced by the Fd allotype with which it is genetically associated. The binding experiments indicated that the genetic association between Fd and Fc allotypes was faithfully reproduced in at least 90% to 95% of γ chains and a search for “recombinant” molecules (A1 with A14 and A15 in an A1, 14/A2, 15 heterozygote) was negative within the limits of the method (5% to 10%). Although a preliminary report (1) suggested that such molecules did occur, these low figures seem to indicate that the formation of “recombinant” molecules which utilize the genetic information for the Fd region from one homologous chromosome and for the Fc region from the other cannot play a major role in generating the diversity of antibody heavy chains.