THE QUANTITATION OF PLATELET-ASSOCIATED IGG ON COHORTS OF PLATELETS SEPARATED FROM HEALTHY-INDIVIDUALS BY BUOYANT DENSITY CENTRIFUGATION

  • 1 January 1982
    • journal article
    • research article
    • Vol. 60  (1) , 136-139
Abstract
As platelets age in the circulation they evidently become progressively smaller and less dense through the loss of protein. The smallest, least dense platelets have a significantly shortened survival, but the mechanism of clearance of these platelets was not known. To evaluate whether the binding of IgG could play a role in the clearance of senescent platelets, platelet size, total protein and platelet-associated IgG was measured on subpopulations of platelets isolated from 6 healthy individuals using a discontinuous iso-osmotic arabinogalactan (stractan) gradient. There was a close correlation between density, size and total protein content (r > 0.9) for all platelet fractions. There was also a relationship between the amount of platelet-associated IgG (PAIgG), total protein and platelet size (r > 0.9) for the first 3 progressively less dense platelet fractions. The 4th platelet fraction containing the smallest, least dense and, on current evidence, oldest platelets had very elevated amounts of IgG. This amount was .apprx. 10 times higher than the mean platelet IgG for the same individual and was similar to the amount of PAIgG found on platelets from patients with immune thrombocytopenia. A progressive increase in the ratio of PAIgG measured after platelet solubilization to PAIgG measured on intact platelets was also noted for the first 3 populations, indirectly suggesting that platelets clear IgG from their surface during aging. Increased binding of IgG to senescent platelets may mediate their destruction.