CD8+, Radiosensitive T Cells of Parental Origin, Oppose Cells Capable of Down-Regulating Cytotoxicity in Murine Acute Lethal Graft-versus-Host Disease

Murine graft-versus-host (GVH) disease takes two forms depending upon the parental/F1 strain combination employed. Anemia, lymphopenia, hypogammaglobulinemia, profound anti-F1 cytotoxicity, and the loss of cytotoxic potential against third party alloantigen is seen in acute lethal GVH disease. In contrast to this, in chronic GVH disease there is polyclonal B cell activation, auto-antibody production, no anti-F1 cytotoxicity, and retained cytotoxicity against allotargets. We have previously reported that this marked disparity in disease expression results from a radiosensitive host veto cell which protects the F1 mouse from parental anti-F1 cytotoxicity in mice undergoing CGVH disease. This cell could be inducedin vitroorin vivoin CGVH disease. Using anin vitrosystem, we now demonstrate that a CD4⁺, radiation-sensitive, T cell does emerge in acute lethal GVH disease which is capable of down-regulating cytotoxicity. The cell does not appear to be a veto cell in that it attenuates cytotoxicity directed against nonself alloantigen. The function of this cell does not appear to be influenced by minor lymphocyte stimulatory gene products. We further report that, in ALGVH disease, regulation by this cell is not readily apparent due to the emergence of a CD8⁺T cell of parental (B6) origin, which opposes its action.