Adherent Mononuclear Cells And Activated Protein C (APC)

Abstract

Addition of bovine APC to dilute whole blood or euglobulin assays of fibrinolytic activity produces little effect on rates of clot lysis. However, addition of APC to undiluted non anti coagulated or to 3.2% citrated whole blood followed by 125I-fibrinogen and thrombin produces clots which release fibrin degradation products and lyse within 24 hours. Ordinarily clotted non-anticoagulated whole blood does not lyse.Addition of increasing amounts of APC from 12-100ug/ml increases the rate of whole blood clot lysis at least 20 fold over a 3.2% citrate control. This response is dose dependent with no evidence of saturation. Addition of increasing amounts of APC (25-200ug/ml) to platelet poor plasma (PPP) increases the rate of clot lysis only twofold. This increase is also dose dependent but is saturated at 80-100ug/ml. Addition of APC (60ug/ml) to 3.2% citrated PPP plus adherent mononuclear cells (1,000-2,000/MM3) again increases the rate of clot lysis at least 20 fold as with the whole blood system. However, this increase in rate is delayed. Substitution of platelet rich plasma (PRP) for PPP eliminates the lag phase. Substitution of non-adherent cells (1,000 MM3), RBC (3 million/MM3) or polymorphonuclear cells produces no acceleration of PPP clot lysis above the PPP-APC control. When deoxyglucose (1.4 × 10-1M) and anti-mycin (2.9 × 10-5M) are added to the PPP plus adherentxells before APC, the cell dependent acceleration of clot lysis is abolished. Removal of plasminogen activator (PA) and plasminogen (P) from PPP by lysine agarose adsorbtion also inhibits the effect of APC and adherent cells whereas reconstitution restores activity to 60%.We conclude that adherent mononuclear cells are required for expression of optimal APC pro-fibrinolytic activity and that this may require both P and PA. This suggests another role for mononuclear cells (monocytes) found in inflamatory and thrombotic lesions.