Lyt-2^+ T cells Modify GVHR Induced by L3T4^+ T cells in MHC Class I Plus II-Disparate Hosts

When B6 T cells are injected into unirradiated (bm1×bm12) F1 hosts, graft-versushost reactions (GVHR) are induced which are classified into two types. The one is MHC class II GVHR induced by L3T4^+ cells and the other is MHC class I GVHR by Lyt- 2^+ cells. When both L3T4^+ and Lyt-2^+ cells were injected into (bm1×bm12) F1 mice, a strong immunodeficient state was induced. Responsiveness to mitogens was abrogated. Class II GVHR showing polyclonal B cell activation was markedly suppressed by inducing class I GVHR simultaneously. The spleen cells of hosts with class II plus class I GVHR showed a marked decrease in IgM^+ cells and an increase in Thy-1^+ Lyt-2^+ cells by flowcytometric analysis. The latter population might function as suppressor and/or cytotoxic cells against host MHC antigens. Significance of the phenomena in the development of autoimmune disease is discussed