Human platelet suspensions can be observed to produce small amounts of H2O2 (0.04 nmoles H2O2/min/2.5 X 10(5) cells/cu mm) and measurable chemiluminescence when exposed to target particles for phagocytosis, such as latex spherules. Both H2O2 production and chemiluminescence are characteristic of phagocytosing polymorphonuclear leukocytes (PMN) and analysis of the purified platelets indicates contamination by PMN at the level of 0.2%. The amount of H2O2 produced and the chemiluminescence observed can be duplicated by adding latex spheres to a preparation of PMN at a concentration equivalent to the contaminant in the platelet preparations. We conclude that the H2O2 produced and chemiluminescence observed from activated platelets is due to the presence of small amounts of contaminating PMN. These studies emphasize the importance of controlling for PMN contamination in studies of platelet biochemistry and physiology.

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