NK suppressive factor in MLC-supernate. I. Defective responsiveness of NK cells from urogenital cancer patients to suppressive MLC-supernates

A soluble suppressive factor (or factors) was demonstrated in the supernate from a 72-h mixed lymphocyte culture (MLC) that exhibited suppressive activity toward the natural killer (NK) activity of allogeneic as well as autologous lymphocytes in vitro, as detected in a 4-h 51Cr release assay on K562 target cells. Suppression of the NK activity reached significant levels when the MLC-supernate was added to the medium at a concentration of 30% (v/v). The percent suppression on NK activity of healthy controls was 23.7±8.7% (mean±SD). The activity of alloactivated lymphocytes to produce a suppressive factor was poor in prostatic cancer (M1 stage) and renal cancer, but not in bladder cancer and prostatic cancer (M0 stage). On the other hand, the NK activity of the lymphocytes from any type of cancers tested was not suppressed by the addition of MLC-supernates from normal individuals. The unresponsiveness was observed even in the early stage of cancer, thus suggesting that a qualitative abnormality might exist in NK cells even from an early stage of Carclnogenesis.