Genetic complementation of histocompatibility-linked Ir genes in the rat

Different inbred rat strains that are congenic with respect to the major histocompatibility system (H-1) show either' a low, an intermediate, or a high immune response to the synthetic polypeptide (H, G)-A--L. Two out of four low responder H-1 haplotypes are found to complement intermediate responsiveness to high responsiveness. This effect is observed for the primary and secondary response and is detectable at the humoral and cellular level, i.e., antibody production and anamnestic response in vitro. Interallelic and intergenic complementation models are outlined. The ensuing implications for H-linked Ir gene control of immune responsiveness and for the structure of major histocompatibility systems are discussed.