Animal model of the insulin-dependent Diabetes mellitus in BB rats: their RT1u homogeneity and prolonged survival of allogeneic skin grafts.

Two substrains of BB rats spontaneously developing the insulin-dependent diabetes-like syndrome were studied. Both the partially inbred BB/K and randombred BB/DK substrains proved RT1u homozygous. Their ancestral WOK stock was shown to be heterogeneous for the RT1u (f = 0.84) and RT1a (f = 0.16) haplotypes. Regarding the H-loci of the RT1 complex, the RT1 haplotype of BB rats seems not to be a recombinant between RT1u and RT1a from the ancestral WOK stock. The generally lowered immune responsiveness of BB recipients to allogeneic skin grafts might be caused by a mutation event at their RT1u haplotype or by some other "major gene(s)" from their genetic background.