Decreased peripheral blood natural killer (NK) cell lytic activity may be associated with tumor presence. We evaluated peripheral blood NK lytic activity in 38 patients with bronchogenic carcinoma and compared this to ten normal volunteers of comparable age. The patients with carcinoma had significantly (P < 0.001) less NK activity (20 ± 17 lytic units at 25% specific lysis)/106 peripheral blood lymphocytes) against the K562 tumor target compared to normal (69 ± 9, SD). NK subpopulations can be defined phenotypically using CD56, CD16, and CD3 monoclonal antibodies and express differing degrees of lytic activity. NK cells from patients with carcinoma had the same absolute number of CD56+ cells and percentage of CD56+CD16+ NK cells (the most lytic subpopulation). However, patients with carcinoma had significantly (P < 0.001) more CD56+CD16-CD3- cells in their overall NK population. This is of note, since this subpopulation is the least lytic. Patient NK cells bound to tumor cells as effectively as those from normal volunteers; however, the maximum rate of kill of patient NK cells was significantly (P < 0.001) less. Thus, decreased NK lytic activity in patients with carcinoma was not due to decreased numbers or proportion of NK cells in peripheral blood or to defective tumor cell binding, but rather to the large CD56+CD16-CD3-NK subpopulation which is characterized by minimal lytic activity. The relation of this NK cell population with the presence of carcinoma is currently under investigation.

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This work was supported by grants from the Cancer Center of the Medical College of Wisconsin and the Midwest Athletes Against Childhood Cancer (MACC) Fund, Milwaukee, WI.

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