HLA-DR is a procoagulant

Numerous incidents of thromboembolic complications have been documented in cancer patients and in recipients of mismatched organ transplants. Tumor procoagulants have also been implicated in the process of metastasis. Two protein bands of 35,000 and 28,000 daltons isolated from human ovarian carcinoma possessed procoagulant activity. The 35,000 dalton protein had an amino terminal sequence identical to that of the major histocompatibility antigen HLA-DR. Further, isolation of the protein using immunoaffinity column chromatography with monoclonal antibody to HLA-DR resulted in the isolation of procoagulant activity. The immunoaffinity purified protein enhanced thrombin generation in recalcified normal plasma approximately 20- fold. HLA-DR procoagulant activity was completely inhibited by Staphylococcal enterotoxin A. We propose that the procoagulant nature of HLA-DR may contribute to thrombotic disorders in several cancers and in association with graft rejection. The ability of enterotoxin A to inhibit this procoagulant may lead to development of future therapeutic strategies.