Native DNA (dsDNA) was found to induce the aggregation of isolated human platelets and the release of platelet 5HT; this activation was inhibited by both theophylline and TYA, suggesting a role for cAMP and metabolic products formed from arachidonate. By contrast, nonaggregating amounts of dsDNA inhibited platelet activation induced by collagen or thrombin. This inhibition, which could be overcome by use of greater amounts of the stimulatory agents, was not associated with the loss of platelet viability. Activation of platelets by dsDNA was not observed in plasma or in isolated platelet systems to which small amounts of cell-free plasma were added. However, dsDNA maintained in plasma its ability to inhibit platelet aggregation induced by collagen and thrombin. RNA and single-stranded DNA failed to induce platelet aggregation or release of 5HT and to block the platelet activation stimulated by dsDNA. Further, dsDNA did not significantly inhibit platelet aggregation in platelet-rich plasma stimulated by ADP or epinephrine. These data implicate dsDNA as a selective and potentially important activator and modulator of platelet responsiveness.

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This work was supported by grants from the National Institutes of Health (AI 12870 and HL 23457) and the Chicago Heart Association. This work was presented in part to the Annual Meeting of the American Association of Immunologists, June 5, 1978 (1).

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