MHC variation and tissue transplantation in fish

Major histocompatibility complex (MHC) genes were originally discovered bec ause of their role in tissue rejection in mammals and have subsequently bee n implicated in the incidence of autoimmune diseases and resistance to infe ctious diseases. Here we present the first demonstration that a gene define d by molecular sequence in the fish MHC, specifically a class II locus, pla ys an important role in tissue rejection. This effect in them endangered Gi la topminnows appears to be additive and depends on the number of MHC allel es shared between the host and the recipient fish of the scale transplants. In addition, there was lower success of scale transplants in MHC-matched i ndividuals in a population with high microsatellite variation than in a pop ulation with low variation. This suggests that other loci, presumably other MHC loci, play a significant role in transplantation success in fishes, as they do in mammals.