Role of the B-G-region antigen in the humoral immune response to the B-F-region antigen of chicken MHC.

In the chicken MHC there exist two regions, designated F and G, which were separated by crossing-over. The F region contains genes controlling all functions characteristic of the MHC. So far only one gene has been assigned to the G region and it is responsible for the presence of an RBC antigen. When cross-immunizing animals of the congenic lines CB and CC with erythrocytes, we have found that both F- and G-specific antibodies were produced. By using the recombinant haplotypes Br1 and Br2 we were able to dissociate the F from the G antigen and immunize with them separately. It was found that production of F antibodies required the copresence of the G antigen, whereas G antibodies were formed regardless of the presence of absence of the F-region antigen. It could be demonstrated that a prerequisite of the role of the G antigen with respect to the F antigen was the localization of both antigens on the same erythrocyte. Possible mechanisms underlying this phenomenon are discussed.