Activation of T and B lymphocytes in vitro. IV. Regulatory influence on specific T cell functions by a thymus extract factor.

In the presence of a preparation of purified thymus extract factors (TEF), spleen cells from athymic nude mice develop in vitro immune responses to soluble DNP-protein conjugates, to particulate sheep red blood cells, and to allogeneic cells. TEF has similar effects also on the in vitro antibody responses of normal mouse spleen cells, enhancing antigen-dependent plaque-forming cells responses to dinitrophenyl carrier complexes of unprimed and primed mice. TEF fails to reconstitute helper cell function in cultures of T cell-deprived spleen cells. The thymic factor increases the reactivity or normal thymus cells in the in vitro mixed lymphocyte reaction and has at high doses mitogenic effects. The role of humoral thymus factors on the differentiation process of T cells is discussed.