Mixed lymphocyte reactions (MLR) in rainbow trout (Salmo gairdneri) sibling.

Suitable conditions for 2 way MLR were determined in random combinations of commercially cultured trout and were then applied to full siblings in two families reared for experimental purposes. The primary aim of the investigation was to determine whether the immunogenetic predictions from mammalian and avian experiments would apply, i.e. (i) that all full sibs, short of rare intra-MHC recombinants, can be assigned to a maximum of four different MHC genotypes, and (ii) that individuals of the same genotype are mutually histocompatible as tested in MLR. If both predictions apply, five or more siblings tested in all pairwise combinations should invariably display compatible pairs, so that a maximum of four groups of mutually incompatible individuals should emerge. The findings did not fit this model, and two alternative immunogenetic models are discussed.