Evidence for two distinct mechanisms in acute fatal graft-versus-host reaction across minor histocompatibility barriers.

The roles of Lyt-1+ and Lyt-2+ T cells in the mechanisms of minor histocompatibility graft-versus-host reaction (MiHL-GvHR), as well as the influence of the source tissues from which those T cells were drawn, have been examined. Using SJL/J recipients H-2 matched to B10.S donors, the responses obtained transplanting donor spleen cells alone, spleen cells mixed with marrow, or lymph nodes mixed with marrow, and treated with anti-Thy-1, anti-Lyt-1, and/or anti-Lyt-2 monoclonal antibodies (MABs) were compared. The results indicated that both Lyt-1+ and Lyt-2+ cells may contribute to MiHL-GvHR and that, at least in part, they may play separate roles. It was also found that when the T cells were derived from the spleen, as opposed to the lymph nodes, there were substantial differences between the observed GvHR survival patterns and in the relative influences of Lyt-1+ versus Lyt-2+ cells on the resultant survival. With the spleen transplant, the Lyt-1+ cells exerted a dominant influence, but with the lymph node transplant, the influence of Lyt-2+ cells was dominant. There was also evidence to suggest the possibility of a Lyt-1 helper-cell contribution to the MiHL-GvHR exhibited by this transplant combination. Finally, it was found that the relative influences of Lyt-1+ and Lyt-2+ cells on MiHL-GvHR were expressed at two distinctly places in the survival curves, the former being seen in the early phase of acute GvHR and the latter at a later phase of the acute response.