Phagocytosis of in vitro-aged erythrocytes--a sharp distinction between activated and normal macrophages.

Phagocytosis experiments performed in vitro in the absence of serum with mouse peritoneal macrophages have shown that normal macrophages can bind to in vitro-aged sheep red blood cells without antibody or complement, but only activated macrophages are able to ingest these erythrocytes. This sharp qualitative functional difference may be an index for the characterization of the activated state of macrophages.