Generation of suppressor cells for natural killer activity in cancer patients after surgery

Natural killer (NK) cell activity was examined in breast cancer patients before and after surgery, and the cells involved in the postoperative depression of cytotoxicity were characterized. NK activity against K562 target cells determined in 4-hour 51Cr release assay of blood lymphocytes from preoperative patients was comparable to that of normal donors. After surgery the patients showed a decrease in NK activity but not in number of large granular lymphocytes in the effector cell populations. When blood mononuclear cells from postoperative patients were depleted of monocytes by adherence to a serum-coated plastic dish and a Sephadex G10 column and then cultured for 24 hours, they showed an increase in NK activity. Furthermore, adherent blood cells of postoperative patients, but not of normal donors or preoperative patients, suppressed the lytic function of NK cells of normal individuals. Twenty-four-hour preculture of suppressor and effector cells was required for suppression of cytotoxicity. Neither postoperative sera nor culture supernatants of suppressor monocytes and effector cells suppressed NK activity. In contrast, the lymphoproliferative response to mitogen was not affected by surgery, and postoperative blood monocytes did not inhibit the mitogenic response of normal lymphocytes. The results suggest that the appearance of suppressor monocytes in the circulation could be one cause of depression of NK activity in postoperative cancer patients.