Measurement of phagocytosis utilizing 51Cr-labeled tannic acid treated erythrocytes

Macrophages recognize and ingest tannic acid treated erythrocytes (TAE) by a mechanism which does not involve the well characterized receptors for immunoglobulin and complement. Since the TAE are susceptible to osmotic lysis, a clear distinction can be made between erythrocytes which are ingested from those attached to the phagocytes' surface. We present a quantitative assay for macrophage phagocytosis using 51Cr-labeled TAE. Uptake of TAE was linearly related to the incubation time during the first 40 min, and increased with the TAE concentration in a log fashion. Furthermore, both attachment and ingestion were positively related to the concentration of tannic acid used to pretreat the erythrocytes. As an example of the application of the method, we compared the ingestion of TAE with that of opsonized erythrocytes (EA) by resident and elicited mouse peritoneal macrophages. While the uptake of EA by thioglycollate-induced macrophages was increased by a factor of approximately 7 over the resident population, the uptake of TAE was only stimulated 2.3-fold. The method will be useful in comparative physiological and pharmacological studies of immunological and non-immunological phagocytosis by macrophages.