Erythrocyte Catabolism in the Inflammatory Peritoneal Monocyte

S ummary . Inflammatory peritoneal exudates were prepared in rats by the intraperitoneal injection of a solution of either casein or methaemalbumin, and 85–95% of the cells harvested from the peritoneal cavities were mononuclear cells. These cells actively phagocytosed antibody‐coated rat erythrocytes containing haemoglobin labelled in vivo with 59 Fe. Erythrocyte phagocytosis occurred rapidly: when the ratio of erythrocytes to monocytes was 1: 8, a mean of 61.7 (± SD 12.5)% of the radioactivity was present in the monocytes within 2 h. The uptake of radioiron introduced into the incubation system in the form of haemoglobin bound to haptoglobin, haem bound to haemopexin, or iron bound to transferrin or ferritin proceeded much more slowly. Monocytes harvested after cither casein or methaemalbumin injection were capable of degrading haemoglobin and transforming up to half the radioiron originally present in haemoglobin into ferritin. A greater proportion of the haemoglobin was degraded by the ‘methaemalbumin monocytes’. Haemoglobin catabolism was accompanied by the formation of approximately equimolar quantities of bilirubin. Most of the radioiron released into the supernatant medium was in the form of either ferritin or haem bound to haemopexin. The behaviour of inflammatory peritoneal monocytes therefore appears to be different from that of liver and spleen reticuloendothelial cells, which release most of the iron derived from erythrocyte haemoglobin catabolism in a form which is available to transferrin. The results of this study may provide an explanation for the increase in plasma haem concentration and the methaemalbuminacmia which has been observed after haemorrhage into the tissues in situations in which there is no intravascular haemolysis and the haptoglobin binding capacity of haemoglobin has not been exceeded