Increased reactivity of responding cells in the mixed lymphocyte reaction by a thymic humoral factor

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Abstract
A thymic humoral factor (THF) induces competence in a certain sector of the lymphoid cell population. The target cell for THF activity was studied using the one‐way mixed lymphocyte culture (MLC). Cells from various lymphoid tissues (responding cells) were preincubated in THF for 1 hour and then mixed with mitomycin‐C‐treated cells (stimulating cells). The results obtained indicate that THF increases MLC competence of lymphocytes from spleen and thymus origin of intact mice and that of spleen of thymus‐deprived mice. In contrast, no enhancing effect in the MLC response by THF could be observed when bone marrow‐derived spleen cells, cortisone‐resistant thymocytes or lymph node cells were used as responding cells. These results confirm our hypothesis that THF leads to differentiation of young thymus‐derived (T) cells, promoting them to maturation and thus to the acquisition of full immune competence.