IS LYMPHOCYTE CO-OPERATION NECESSARY FOR THROMBOPLASTIN SYNTHESIS BY HUMAN-MONOCYTES

  • 1 January 1983
    • journal article
    • research article
    • Vol. 53  (3) , 731-738
Abstract
Human monocytes synthesize the protein component of thromboplastin and express increased procoagulant activity when appropriately stimulated in vitro. The activity reached maximum between 2 and 20 h depending on the stimulant used. The presence of lymphocytes (lymphocyte:monocyte ratio 4:1) enhanced this activity only very slightly (up to 1.3-fold) at the time of maximal monocyte thromboplastin expression. Lymphocytes had a marked potentiating effect on PHA [phytohemagglutinin] stimulation that became clearly evident after 12 h, at which time the thromboplastin response of monocytes alone to PHA had subsided. The thromboplastin activity of monocytes remained at a high level for 24-40 h in the presence of PHA or endotoxin and lymphocytes, but lymphocytes did not influence the early (4-8 h) thromboplastin response. Neither did lymphocytes alter the magnitude or the time course of the response when monocytes were stimulated with PPD [purified protein derivative], TPA [12-O-tetradecanoyl-phorbol-13-acetate] or immune complexes. The lymphoblastoid cell line Molt 4 [human leukemia] (T cell like) was as effective as lymphocytes, Daudi [Burkitt''s lymphoma] cells (B cell like) were slightly less effective. The enhancement of thromboplastin activity in PHA-stimulated monocytes could be induced also by conditioned medium from PHA stimulated lymphocytes. Freshly isolated monocytes synthesize thromboplastin directly upon interaction with a stimulant, and are not dependent on a helper effect of lymphocytes or lymphocyte products. Such help, however, will prolong the ability of the monocytes to respond.