PA-IgG on platelet subpopulations of different buoyant densities: high levels on the low density population is an artifact.

We isolated subpopulations of normal blood platelets from platelet rich plasma (PRP) and, in parallel, from platelet rich saline (PRS) on the basis of their buoyant densities. The MPV, being smallest in the lightest subpopulation, correlated significantly with platelet buoyant density (P < 0.002). In agreement with previous reports, we showed that the least dense platelet subpopulation, separated from PRP, had a high level of PA-IgG (3,486 mol/plt). This value was significantly greater (P < 0.02) than PA-IgG in the lightest subpopulation separated from PRS (693 mol/plt). We believe that the procedure of separating platelets from PRP artificially increased PA-IgG in the least dense subpopulation. Our data showed that when subpopulations were prepared from PRS, PA-IgG correlated with platelet buoyant density (P < 0.002), and that the subpopulation with the highest density had the highest level of PA-IgG.