Polygenic control of mixed lymphocyte reaction in dogs.

The genetics of the MLR of the dog are studied using LD typing cells. The four new homozygous reference cells described bring the total number of defined LD specificities in this species to 11. In families, LD specificities generally segregate en block with the SD specificities of the DLA complex. The recombination frequency between the SD and LD loci is provisionally estimated to be 0.007. A slight but significant stimulation between two SD identical LD typed siblings could not be explained on the basis of a single recombination between the SD loci and one LD locus and therefore suggested the existence of an additional LD system. Unrelated SD different individuals with two different LD determinants in common frequently stimulate each other in MLR, but low responses are also encountered. The results described are compatible with a hypothesis of two segregant series of alleles for the genetic control of the MLR and linkage disequilibrium between certain alleles of these series. More conclusive evidence of the validity of this hypothesis and further knowledge of other factors which determine the response in the MLR are required before a reliable estimate of the importance of LD structures in histocompatibility can be made.