Phenotypic and functional analyses of natural killer cells: Impaired NK activity partly due to the CD56+cell dysfunction in cancer patients

Natural killer (NK) cells are cytolytic effecters that are capable of killi ng tumor or virus-infected cells. To determine whether the differences in N K function could be detected among cancer patients who received immunothera py using interferon-alpha, we assessed NK activity against K562 target cell s by flow cytometry. We found significantly lower values in cancer patients compared with those in healthy subjects. When cancer patients were classif ied into various clinical groups, patients with progressive tumors and pati ents at cancer stage IV showed a statistically significant impairment in NK function. The lymphocyte subset predominantly responsible for cytolysis ag ainst K562 was found to be the CD56+ cells. Analysis of NK activity with th e number of CD56+ cells contained in peripheral blood lymphocytes (PBLs) sh owed a positive correlation between these two factors in healthy controls b ut weak or null correlation in cancer patients. The incidence of impaired N K activity observed in cancer patients could not necessarily be correlated with the number of the CD56+ cells in PBLs: NK activity per single CD56+ ce ll decreased markedly in groups exhibiting impaired NK function. These obse rvations demonstrate that differences existed in NK activity among cancer p atients and that the depression of NK activity was partly due to a deficien cy in the functional ability of CD56+ cells.