Macrophage Heterogeneity in Thromboplastin Response

The procoagulant activities of non‐elicited mouse monocytes/macrophages from four anatomical localizations were compared. These cell populations were further examined for their ability to increase their procoagulant activity on exposure to endotoxin or phytohaemagglutinin (PHA). Peritoneal macrophages exhibited the highest basal procoagulant activity. Their activity was further enhanced by stimulation with endotoxin and PHA, but marked strain differences were noted. This procoagulant has been identified as tissue thromboplastin. Isolated adherent spleen cells, peripheral blood monocytes or lung alveolar macrophages had a low basal procoagulant activity that did not increase on exposure to PHA or endotoxin. The identity of the weak procoagulant in these cells is uncertain. The presence of lymphocytes in the macrophage cultures (4:1 ratio) enhanced slightly (1.3 to 1.5‐fold) the response of peritoneal macrophages to endotoxin or PHA but did not significantly influence the procoagulant activity of the other macrophage subpopulations under the conditions tested. These results demonstrate heterogeneity among different macrophage subpopulations with regard to cellular procoagulant expression.