SUBSETS OF T CELLS IN THE RAT MEDIATING LETHAL GRAFT-VERSUS-HOST DISEASE

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Abstract
Mouse monoclonal antibodies that recognize rat thymocyte membrane antigens define 2 nonoverlapping subsets of rat periperal T cells. These T cell subsets mediate different immunological functions and are probably analogous to the Lyt-2+ and Lyt-2- subsets in the mouse. The activity of these 2 T cell subsets in mediating graft-vs.-host disease (GVHD) in rats is reported; the role played by donor B cells is examined. Parental strain thoracic duct lymphocytes were depleted of one or other of the 2 subsets, and the residual cells transferred to sublethally irradiated F1 recipients. With 1 subset, known to contain the precursors of cytotoxic T cells, the disease, although usually fatal, tended to run a rather protracted course. In contrast, the subset containing helper T cells and cells that proliferate strongly in the mixed lymphocyte reaction caused a disease that was as rapidly fatal as that resulting from the injection of unfractionated donor cells. The activity of this subset was uninfluenced by the presence or absence of donor B cells. Recipients of parental lymphocytes depleted of both T cell subsets showed no evidence of disease and gained weight at the same rate as rats given no parental cells. GVHD apparently can be mediated by more than 1 type of effector T cell. Although cytotoxic T cells of donor origin may be capable of mediating lethal GVHD, these cells apparently play no indispensable role in this condition.