Phagocytosis of monocytes in cancer patients.

The phagocytic activity of monocytes directed at yeast particles was investigated in patients with untreated malignant tumors and in normal controls. Phagocytic activity was found to be significantly increased in the patients. It could be shown that the increased activity is caused by factors contained in the patient's plasma. These factors are only partly destroyed by heat inactivation, suggesting that both heat labile and heat stabile factors are contributing to the observed enhancing effect on phagocytic activity. The heat labile portion could well be the complement component C5, while the heat stabile portion is so far undefined.