The endotoxin-induced coagulant activity of human monocytes.

Leucocyte suspensions, exposed to endotoxin in vitro, develop coagulant activity which has been identified as tissue factor. Pure suspensions of polymorphonuclear (PMN) neutrophils, lymphocytes and monocytes were exposed to endotoxin and tested for tissue factor activity after 4 h incubation at 37 degrees C. The results indicate that the monocyte is the cell primarily responsible for the endotoxin-induced coagulant activity of mixed leucocyte suspensions, the small amount of activity demonstrated in PMN neutrophil and in lymphocyte suspensions at high cell concentrations being accounted for by monocyte contamination of less than 1%.