Lymphocytopoietic factor in lymph.

The evidences which suggest the presence of a lymphocytopietic factor in rat thoracic duct lymph are summarized briefly. The intravenous injections of the extracted materials from lymph plamsa into syngeneic recipient rats resulted in the massive proliferation of lymphoid cells predominantly in the thymus dependent areas and thymic cortex, suggesting that the target cells for the factor are not marrow-derived (B) cells, but thymus derived (T) cells. The existence of a thymus is not necessarily required for the production or secretion of the factor. The augmenting effect of the factor on T cell functions, eg. local graft-versus-host rection and helper activity of plaque forming response to sheep erythrocytes, is mentioned. The physicochemical characteristics of the factor are nondialysable and heat-stable glyco-protein molecules. The roles of lymph humoral factor in T cell-differentiation or proliferation are discussed.