Effects of non-major histocompatibility antigens on acute graft-versus-host reaction after allogeneic bone marrow transplantation.

In the present study using an experimental BMT system we analyzed the effects of disparity at non-MHC Ag including minor lymphocyte stimulatory-1a (Mls-1a) Ag on the acute GVH reaction (GVHR) induced by MHC class I Ag. Mismatch at MHC (class I) Ag alone did not induce clinically detectable acute GVHR in this model. However, BMT mice prepared with a combination of both class I and non-MHC Ag mismatches showed signs of clinical GVHR and various cytokines were produced by the spleen cells at an early stage (4 days) after BMT. Although no clinical GVHR was detected in BMT chimeras prepared with a non-MHC mismatched but MHC matched combination, large amounts of various cytokines were secreted by spleen cells. Cytokine production in the latter two kinds of chimeras paralleled the increase of Mls-1a reactive Vbeta6+ T cells in the host spleen. Marked cytokine production induced by Mls-1a Ag was confirmed by MLR. Thus, these cytokines appeared to be produced by T cells responding to Mls-1a (ie Vbeta6+ T cells) and to augment the T cell responses to MHC class I which resulted in clinically detectable GVHR in chimeras prepared with the combination mismatched at both MHC class I and non-MHC loci.