An inhibitor of blood coagulation, a new protein with an apparent molecular weight of 34,000 and an isoelectric point of 4.9, was purified from human placental tissue by EDTA extraction. Five cDNA clones were isolated from the human placental lambda gt11 cDNA library using the mouse monoclonal antibody raised against the coagulation inhibitor as the probe. The longest insert consists of 1,566 nucleotides, and contains 960 nucleotides entirely encoding the 320 amino acids of the inhibitor, and a poly A tail. The deduced amino acid sequence was corroborated by chemical analyses of the protein. The entire amino acid sequence shows homology to those of lipocortin I, lipocortin II, and endonexin-related proteins. The cDNA for the inhibitor was expressed in Escherichia coli under the regulation of the trc promotor of the plasmid pKK233-2. The resulting recombinant protein manifested inhibitory activities against both blood coagulation and phospholipase A2 activity, as did the coagulation inhibitor isolated from human placenta.

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Anti-annexin V (anti-ANXV) IgG and lupus anticoagulant (LAC) were both shown to be capable of inducing apoptosis in umbilical vein endothelial cells [Nakamura et al.: Biochem Biophys Res Commun 205:1488-1493, 1994]. In the present study, we have demonstrated that anti-ANXV IgG prolongs the activated partial thromboplastin time and has an affinity for phospholipids in enzyme-linked immunosorbent assay. This indicates overlapping of anti-ANXV and LAC activities, suggesting that ANXV may be involved in the autoimmune mechanism for LAC production.

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