Inhibition of cell-mediated immunity by tumour cell products: depression of interleukin-2 production and responses to interleukin-2 by mouse spleen cells.

Supernatants from cultures of mouse and human tumour cells inhibited the production of interleukin-2 (IL-2) by stimulated mouse spleen cells. The tumour cells tested, all of which were active, included a mouse and a human melanoma, three methylcholanthrene-induced fibrosarcomas of mice, and human HeLa cells. Supernatants from normal mouse and human fibroblasts were inactive. Inhibition was dose-dependent. Spleen cells from aged mice were more susceptible to inhibition than spleen cells from young mice. When tumour cell culture supernatants were fractionated on Sephacryl S-300, two peaks of activity were found, with apparent molecular weights of approximately 50 and 18 kD. Supernatants from tumour cell and fibroblast cultures caused variable, but generally weak, inhibition of responses of lymphoblasts to IL-2. It is suggested that inhibition of IL-2 production may be an important mode of action of tumour cell products that inhibit cell-mediated immunity.