Purification and functional characterization of a low molecular weight immune modulating factor produced by Lewis lung carcinoma.

Previously, we reported that mouse tumors contain a low molecular weight factor which is capable of affecting in vitro properties of macrophages. We now describe the purification to homogeneity of the only factor with macrophage modulating activity from one of these tumors Lewis lung carcinoma. The purified tumor factor appears to be a carboxylic acid and it retains all of the macrophage modulating properties which are characteristic of the unfractionated crude tumor extracts. This factor therefore reverses the spreading of macrophages, enhances the migration of macrophages out of capillary tubes and inhibits their chemotactic and tumoricidal activities. The purified tumor factor also inhibits immune responses of spleen cells. Specifically, proliferation of normal lymphocytes in response to mitogens and to alloantigens, as well as the generation of cytotoxic T lymphocytes in a mixed leukocyte culture, are suppressed when these cells are cultured in the presence of the purified tumor factor. The mixed leukocyte reaction of lymphoid cells obtained from mice which had been treated with the tumor factor is reduced compared to the response of lymphocytes obtained from normal mice. It is possible that there is a relation between production of this factor by tumor cells and survival of the tumor in a host.