Generation of procoagulant activity by mononuclear phagocytes: a possible mechanism contributing to blood clotting activation within malignant tissues.

This study investigated the procoagulant activity (PCA) of mononuclear phagocytes from rabbits bearing the V2 carcinoma. Macrophages harvested from either intraperitoneally or subcutaneously growing tumors were found to express a very strong procoagulant activity as compared with peritoneal macrophages and circulating mononuclear cells from the same animals. On the other hand, when incubated with or without endotoxin in short-term cultures, circulating mononuclear cells from tumor-bearing animals generated significantly more procoagulant activity than those from control animals. In all instances, procoagulant activity was identified as tissue factor by using assay systems with plasmas selectively deficient in the various clotting factors. These results indicate that, besides cancer cells, mononuclear phagocytes might also play an important role in the activation of blood coagulation and in the deposition of fibrin at the host-tumor interface.