[Effect of cancerous ascites on natural killer activity]

The effect of cancerous ascites on NK activity was evaluated by a 12-hr exposure method. Erythroleukemia cell line, K 562, was used as the target cells, the effector cells were isolated from 34 healthy volunteers. The final protein concentration of ascites was adjusted to 0.02, 0.2 and 2.0 mg/ml, after centrifugation and membrane filtration. When ascites was added at the start of assay, NK activity was almost completely suppressed by cancerous ascites of 2.0 mg/ml; it was not suppressed by 0.02, 0.2 mg/ml. No suppression was found when cancerous ascites was added 6 hrs after the start of assay. Our results suggest that the lowered NK activity of cancer patients may be attributable to unknown factor (s) released from cancer cells.