A major histocompatibility locus in fish: serological identification and segregation of transplantation antigens in the common carp (Cyprinus carpio L.).

In this study, experiments are described that were designed to investigate whether fish have an immune regulatory systems similar to the major histocompatibility complex (MHC) in higher vertebrate species. From combinations of gynogenetic carp showing either slow or fast rejection of skin transplants, the latter were chosen for alloantiserum production by hyperimmunization with peripheral blood leucocytes. The resulting alloantisera were analyzed for hemagglutinating reactivity with gynogenetic siblings and proved to be operationally monospecific in absorption experiments. The serologically determined carp erythrocyte specificities were shown to correspond to two codominantly expressed allelic products of a single locus and were designated K1 and K2, respectively. Flow cytometer analysis revealed that the same products are also present on leucocytes from peripheral blood, thymus, spleen, and pronephros. K1- and K2-homozygous second-generation gynogenetic siblings were used to study the histocompatibility nature of the K locus products. Skin transplants between K-allogeneic gynogenetic siblings were rejected significantly faster than within K-syngeneic combinations. Taken together, these data suggest that the K locus incorporates MHC class I-like characteristics.