The long-range goal of this work is to obtain a better understanding of molecular mechanisms involved in cell mediated immunity. Emphasis will be placed on the nature and activity of a suppressor factor produced by a lymphoblast T-cell line. Evidence supporting the suppressor T-cell hypothesis is presented in this proposal. Experiments will be conducted to determine the chararacteristics of this factor and its mechanism of action. Studies will also be initiated to determine the mechanics of the exceptional stimulation by lymphoblast B-cell lines as compared to poorly stimulating T-cell lines. Lymphoblast cell lines will also be investigated for use as targets in cell mediated lympholysis, where normal human lymphocytes have been found to be specifically cytotoxic to some lines in the absence of in- vitro stimulation. The experimental hypothesis that presensitization can normally occur to blast or tumor associated antigens will be tested. Correlations will also be sought between sensitized lymphocytes and disease states of donors. This type of cytotoxicity will also be compared with other known cellular immune mechanisms in an attempt to build a molecular model for cell mediated lympholysis. The studies on immune suppression are desired to shed additional light on the normal regulation of the immune response as well as for their potential benefits in transplantation and carcinogenesis. Studies on lympholysis of lymphoblast cell lines may lead to a better understanding of immune surveillance mechanisms.