The formation of a thrombin-like material (TLM) following stimulation of leukocytes.

When thrombin, tissue thromboplastin or Russell's viper venom was added to a suspension of either lymphocytes or neutrophils containing normal plasma, aggregation of these cells ensued. The aggregate formed one gelatinous mass which was readily separable from the cell free supernatant, an aliquot of which caused platelet aggregation. This leukocyte derived platelet aggregatory substance had characteristics similar to thrombin but not AGEPC. When plasma deficient in Factor V was substituted for normal plasma, the platelet stimulatory substance was not produced. Substitution with plasma deficient in Factor VII, VIII, IX, X or XI was without effect. Thrombin clotting time measurements indicated a generation of activity, relative to thrombin, of about 3.0 U/5 X 10(6) cells.