Rat erythrocytes elicit antibody formation against RT1.A region-determined antigens in allogeneic recipients

Highly purified erythrocytes of inbred LEW (RT1(1)) rats (LEW-E) elicited antibody responses in inbred BN (RT1n) rats. Intravenous infusion of 1 X 10(8) LEW-E elicited IgM haemagglutinins and after one further infusion of LEW-E IgG haemagglutinins were raised as well. These haemagglutinins were mainly directed to RT1.A region-determined classical transplantation antigens but a weak response to non-RT1 minor histocompatibility antigens was also obtained. In the reciprocal combination erythrocytes of BN and LEW.1N rats, which carry the RT1n haplotype on the LEW strain genetic background, infused into LEW rats yielded strong IgM haemagglutinin responses to RT1.A antigens only but failed to elicit IgG antibody. Infusion of LEW.1N rats with LEW-E elicited only weak IgM haemagglutinin responses. These findings demonstrate that RT1.A antigens are immunogenic for they elicit IgM alloantibody responses. IgG haemagglutinin responses to LEW-E may depend on the presence of minor histocompatibility antigens in conjunction with RT1.A antigens on LEW-E or alternatively on control by Ir-genes located outside the RT1 complex.