Ability of H 2 regions to induce graft vs host disease

Individual young adult F₁ hybrid mice were irradiated with 500 R and 24 hr later injected with 5 x 10⁷ spleen cells obtained from a sex matched parental strain donor. The injected animals were then followed for a period of 3 mth and loss of body weight, mortality rate, and other signs of fatal graft vs host disease (GVHD) were recorded. The donor recipient strain combinations were selected in such a way as to provide genetic differences in the entire H 2 complex, the K or D regions alone, the K or the D end, and the central (I) regions alone. The data obtained on only few combinations indicate that strong GVHD (100% mortality rate within the 1st mth after the injection) occurs only in those donor recipient combinations which differ in the entire H 2 complex or in the K end (K + I regions). Much weaker GVHD (mortality rate of only 50% or less and death of individual mice spread over the entire observation period) is observed when the donor and the host differ in either the K, I, or D region alone. The degree of GVHD induced by 3 regions, when taken singularly, is about the same. Surprisingly, the K region GVHD was somewhat stronger in combinations of mutant strains in comparison with recombinant strain combinations.