Generation of procoagulant activity by hairy cells in response to endotoxin and phorbol esters

Several investigators have suggested that hairy cells are neoplastic B lymphocytes. These cells, however, also share some biological properties with mononuclear phagocytes. A property of these cells is the capacity to generate procoagulant activity (PCA) in response to a variety of stimuli. In this study we investigated the PCA of peripheral blood hairy cells in 19 consecutive patients with hairy cell leukaemia (HCL). Monocyte-depleted blood mononuclear cells, tested immediately after isolation, expressed little, if any, activity. However, after exposure to endotoxin, a marked increase in PCA was observed (42.1 +/- 8.7 vs 1.3 +/- 0.2 units/5 X 10(1) hairy cells). A significant correlation was found between the number of lymphocytes/hairy cell and the level of endotoxin-induced PCA suggesting that lymphocytes potentiate the procoagulant response of hairy cells. When stimulated with 12-0-tetradecanoyl-phorbol-13-acetate (TPA), patients' cells produced about 2-8 times more PCA than endotoxin-stimulated cells. The PCA induced by endotoxin and TPA was identified as tissue factor. These findings suggest some further relationship between hairy cells and monocytes.