Modulation of human monocyte leukotactic responsiveness by thromboxane A2 and 12-hydroxyheptadecatrienoic acid (12-HHT).

The leukotactic responsiveness of human peripheral blood monocytes is regulated by the cell-directed inhibitor of monocyte leukotaxis, CDI-MLx. The actions of CDI-MLx on normal monocytes in vitro were abrogated by co-incubation with inhibitors of cyclooxygenase and thromboxane synthetase with indomethacin and dazmegrel (UK-38,485) being most active. The actions of CDI-MLx were mimicked by the thromboxane A2 analogue, U-46619, and by 12-HHT with half-maximal inhibition observed at 10(-10) M; PGE2 was 1000-fold less active. SQ 29,548, a thromboxane A2 receptor antagonist, blocked the effects of CDI-MLx, U-46619, and 12-HHT. Production of PGE2 and thromboxane B2 by purified monocytes was stimulated by CDI-MLx and this effect was also blocked by indomethacin, dazmegrel, and dazoxiben. These data suggest a major regulatory role for thromboxane synthetase products in human monocyte leukotaxis.