Histocompatibility in the rabbit. The effect of imbreeding on skin graft survival time

Skin grafts were exchanged between siblings from 16 inbreeding lines of rabbits. Progressive inbreeding and genome fixation through 12 generations of brother X sister matings does not produce a concomitant increase in graft survival time but instead produces a heterogenous response reflecting the residual segregation of individual histocompatibility loci. Grafts exchanged between RL-A incompatible siblings were not maintained for more than 12 days, regardless of the degree of inbreeding. The frequency distributions of the survival times of grafts exchanged between animals from all inbreeding lines from each generation, F5 through F8, agree best with the expected values calculated by assuming that 17 independent histocompatibility loci, with 95% confidence limits of 11 and 28 loci, must be matched to assure acceptance of skin grafts for 60 days or more. However, in animals from line Sh5b, only 3 significant histocompatibility loci appear to be segregating. Two of the significant histocompatibility loci segregating in line Sh5b have not geen identified;the third significant locus is either the Hg blood group locus or is linked to the Hg locus. Established loci that remain polymorphic during intensive inbreeding may be important in the development of a model transplantation system; as inbreeding progresses these established loci may be maekers for histocompatiblity loci thathave a significant effect on allograft survival time.