Phagocytosis by human blood leukocytes measured by the uptake of 131I-labeled human serum albumin: inhibitory and stimulatory effects of cytochalasin B.

In the study of phagocytosis, the experimental systems used must be able to distinguish among various aspects of the phagocytic process, such as chemotaxis, adherence of the ingestate, engulfment, fusion of phagosome and lysosome, metabolic perturbations, and extracellular release of various substances. Chang introduced a method for measuring the degree of ingestion of starch particles by rabbit exudate granulocytes in vitro, by the concomitant uptake of radioiodinated (1311) human serum albumin (1). This method was sensitive and quantitative, and was particularly useful for distinguishing adherent from ingested particles, since, even if surface particles could not be dislodged, radioactive label in the media could be washed away. We have modified this method in a study of phagocytosis by human blood leukocytes in vitro, and employed it to emphasize the importance of the particle ingested, in the results obtained. In using the mold metabolite, cytochalasin B, to modify ingestion, we have found particle-dependent stimulatory as well as inhibitory effects of the drug, which have similarities to effects of cytochalasin B in other systems, but were not detected in previous studies of the effects of that drug on phagocytosis (2-7).