Serum factors which suppress natural cytotoxicity in cancer patients.

Spontaneous cytotoxicity mediated by natural killer (NK) cells is potentially an important mechanism of immunosurveillance against tumor or virus-infected cells. NK activity is impaired in many cancer patients. This study investigated the possibility that humoral factors are responsible for depressed NK activity in cancer patients and examined whether these factors were anti-lymphocyte antibodies (ALA) or immune complexes. The degree of NK suppression induced by 20 cancer patients' sera was determined by preincubating normal peripheral blood mononuclear cells with cancer sera. Eight of the 20 serum samples from cancer patients had NK-suppressive humoral factors. Elimination of immune aggregates by ultracentrifugation did not remove the inhibitory factors. The degree of NK suppression induced by cancer sera correlated with the extent of NK impairment in the serum donors (p less than 0.05). The cancer sera was examined for the presence of ALAs using flow cytometry. All cancer sera tested contained only low ALA reactivity to NK cell-enriched suspensions (less than 15%). This is in marked contrast to previous reports regarding NK-inhibitory systemic lupus erythematosus sera which contained large amounts of large granular lymphocyte (LGL) reactive ALAs. This study demonstrates that certain cancer sera suppress NK cell function. These inhibitory serum factors do not appear to be LGL-reactive ALAs or immune aggregates.