Studies of the Release Reaction Induced by Cell Contact in Platelets from Patients with Systemic Lupus Erythematosus
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Blood platelets-respond to a variety of chemicals and proteins, including immunoglobulin G (IgG) by changing shape from a disc to a sphere, aggregating to form a platelet plug, and releasing the stored contents of their intracellular organelles (the release reaction). Whether the interaction of IgG with platelets can cause the release reaction depends on the extracellular environment of the platelet and the nature of the IgG. Small soluble IgG aggregates or small immune complexes will bind to the surface of platelets, but will only cause platelet release if the platelets are brought into contact with each other by centrifugation. In phase I of this study, platelets from patients with systemic lupus erythematosus, which have been shown to bind significantly more IgG to their surface than platelets from non-lupus controls, released greater amounts of 14-C-serotonin than platelets from non- lupus individuals upon cell contact by centrifugation. Phase II of this study attempted to locate the cause of the greater release of lupus platelets to a factor on lupus platelets, or a factor in lupus plasma. Comparisons of lupus and control platelet releases after the platelets had been resuspended into lupus plasma, control plasma, or buffer showed no statistically significant difference in release. Release of the contents of lupus platelet intracellular organelles in vivo may contribute to the pathogenesis of lupus kidney disease (lupus nephritis).