ANTIMICROBIAL PROTEINS OF NEUTROPHILS AS REGULATORS OF PLATELET ACTIVITY

The effects of antimicrobial proteins of neutrophils [human defensins (HNP), rabbit defensins (NP) and human lactoferrin (LF)] on platelet a ggregation and cytoplasmic free Ca2+ levels ([Ca2+]i) have been studie d. The results show that HNP (0.1 to 40.0 mu g/ml) or NP (0.1 to 100.0 mu g/ml) were unable to trigger platelet aggregation and [Ca2+]i chan ge. However, HNP (40.0 mu g/ml) reduced thrombin, collagen and ADP-ind uced aggregation of washed platelets as well as the [Ca2+]i increase c aused by thrombin, ADP and LPS. NP inhibited [Ca2+]i increase in ADP- or LPS-stimuiated platelets too. Nevertheless, it was not accompanied by a reduction of platelet aggregation. LF in the concentration range from 0.1 mu g/ml to 100.0 mu g/ml did not influence the platelet activ ation induced by thrombin, ADP, collagen or LPS. Participation of if i n the regulation of platelet activity was observed only with a high co ncentration (200.0 mu g/ml) of protein and was expressed as a (Ca2+]i increase. These data show that defensins and if participate in neutrop hil-mediated modulation of platelet functional activity.