Kinetics of thymus-derived lymphocyte count changes in rats affected by graft-versus-host reaction.

The effect of GVHR on thymus-dependent lymphocytes of various lymphoid organs has been followed autoradiographically and by scintillation technique in a temporal dependence on the induction of the reaction. GVHR was induced in (BD X Lw) F1 hybrid rats with parental spleen (BD) cells. As marker of the thymus-dependent lymphocytes the in vitro 3H-uridine incorporation was used. Compared to B cells, T lymphocytes of rats have a higher ability of incorporating labeled uridine. T lymphocytes in peripheral blood and the thoracic duct achieved their peak at 3 or 4 days following GVHR induction. On the fourth day, simultaneously with a GVH-altered thymus a rapid decline in the number of these cells was also observed. A mobilization of T lymphocytes from the spleen and lymph nodes into the circulation already in the very first days of the reaction might be responsible for the peak seen in PBL and TDL. The GVH-alteration lasting 21 days caused an evident reduction of thymus-dependent lymphocytes in all the organs studied here. The immunological attack of GVHR is considered to be primarily responsible for the exhaustion of T cells. The discussion bears on the possibility of a more progressive action of GVHR on the more mature T lymphocyte subpopulation.