DECREASED ARACHIDONIC-ACID METABOLISM IN HUMAN PLATELETS BY AUTOLOGOUS NEUTROPHILS - POSSIBLE ROLE OF CELL-ADHESION

The amount of the 12-lipoxygenase and cyclo-oxygenase products, 12(S)- hydroxy-(Z,Z,E,Z)-5,8,10,14-eicosatetraenoic acid (12-HETE) and 12(S)- hydroxy-(E,E,Z)-5,8,10-heptadecatrienoic acid (HHT), in human platelet s stimulated by thrombin (0.1 and 2.5 units/ml), was studied in the pr esence of autologous neutrophils. A decreased formation of both produc ts was induced by unstimulated neutrophils or neutrophils challenged w ith N-formylmethionyl-leucyl-phenylalanine (0.1 mu M) or Ca2+ ionophor e A23187 (0.15 mu M). The effect of neutrophils was observed only in t he presence of Ca2+. 12-HETE and HHT were also produced in platelets s timulated with thrombin in the absence of Ca2+ and/or Mg2+, but their level was not altered by neutrophils. ,20-Dihydroxy-(Z,Z,E,Z)-5,8,10,1 4-eicosatetraenoic acid (12,20-DHETE), the cytochrome P-450 product fr om 12-HETE in neutrophils, was hardly detected, and its level did not compensate for the decrease in 12-HETE observed after platelet and neu trophil co-incubation. 5(S),12(S)-Dihydroxy-(E,Z,E,Z)-6,8,10, 14-eicos atetraenoic acid (5(S),12(S)-DHETE), the 5-lipoxygenase product of 12- HETE in neutrophils, was never detectable. In addition, the inhibition of 12-HETE and HHT formations appeared not to be due to degradation o r thrombin uptake by neutrophils, nor was the decrease observed when t he two cell populations were physically separated. A monoclonal antibo dy against the human platelet glycoprotein GMP140 (CD62), mediating Ca 2+-dependent platelet-neutrophil adhesion, mimicked the inhibitory eff ect of neutrophils in a dose-dependent fashion. Furthermore, the 12-HE TE and HHT productions were not affected when platelets were stimulate d in the presence of neutrophils previously incubated with sialidase, which removes the sialic acid from a sialyl Lewis(x) structure assumed to be the neutrophil receptor for platelet GMP140. We conclude that t he decrease in thrombin-stimulated 12-HETE and HHT formation observed when platelets were co-incubated with autologous neutrophils might be the consequence of platelet-neutrophil adherence, presumably through p latelet GMP140.