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Anti-Annexin V

Annexins are a family of calcium-dependent phospholipid-binding proteins. They are abundant in the eukaryotic kingdom.Though structurally well investigated the in vivo function of the annexins is still unclear.. They definitively belong to a family of ubiquitous cytoplasmic proteins involved in signal transduction. All annexins have been shown to have putative binding site for protein kinases C but only annexin V would possess a potential pseudo-substrate site. Thus annexin V seems to modulate the activity of some PKCs on thein substrates. Annexin V was found to play a major role in matrix vesicle-initiated cartilage calcification as a collage-regulated calcium channel. Annexin V’s preferential binding partner is phosphatidylserine (PS). PS is predominantly located in membrane leaflets, which face the cytosol. However, recent findings show that each cell type has the molecular machinery to expose PS at its cell surface. This machinery is activated during the execution of apoptosis. Once PS is exposed at the cell surface it exhibits procoagulant and proinflammatory activities. Annexin V will bind to the PS-exposing apoptotic cell and can inhibit the procoagulant and proinflammatory activities of the dying cell. These findings together with the presence of Annexin V in the extracellular space depict a novel pathophysiological significance for Annexin V in vivo. The occurrence of autoantibodies to annexin V has been described in several pathological disorders. It is concluded that extracellular annexin V provides an antigenic stimulus for autoantibody production. Such autoantibodies may have a detrimental role interfering with putative functions of annexin V. So it has been shown that concentration of anti-annexin V autoantibodies were significantly raised in sera from patients with rheumatoid arthritis compared to normal controls. Elevation in the anti-Annexin V levels were furthermore detected in patients with Systemic lupus erythematosus (SLE), in these CASE higher incidences of arterial or venous thrombosis, intrauterine fetal loss and prolonged activated partial thromboplastin time were found (5,6). Anti-annexin V antibodies in sera from patients with lupus anticoagulant (LAC) were shown to exhibit anti-phospholipid and LAC properties. The presence of antibodies to Annexin V has furthermore been hypothesized to play a role in recurrent abortions, preeclampsia and fetal death.

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