Opsonized‐zymosan induces a respiratory burst in human blood platelets

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Abstract
Opsonized‐zymosan‐stimulated polymorphonuclear cells show a cyanide‐insensitive oxygen consumption. We have investigated whether opsonized‐zymosan could induce similar metabolic change in human blood platelets. Preparation of intact human blood platelets, obtained by separation through a Ficoll layer (23% w/v) were challenged with opsonized‐zymosan. the polymorphonuclear cell contamination was less than 1/108 platelets. The opsonized‐zymosan‐stimulated platelets showed an increase of oxygen consumption. The mean of xygen burst measured by a polarographic method with a Clark electrode was 11 nmole/109 platelets/min (S.E.M. 4; n = 15). The duration of the burst was 2 min. Unstimulated platelets did not show the oxygen burst. The inhibitors of respiratory chain and prostaglandin synthesis completely abolished the oxygen consumption by opsonized‐zymosan‐stimulated platelets. The simultaneous addition of NADH (1 mM) and opsonized‐zymosan induced a burst of oxygen consumption, which occurred after a variable lag phase (10‐2 min) from the stimulation, also in the presence of inhibitors. This burst, which lasted about 1 min. amounted to 10 nmole/109 platelets/min (S.E.M. 2; n = 15) and it was higher in the presence of NAN3 a catalase inhibitor. Zymosan treated with hydrazine or heated plasma (56°C) did not cause increased oxygen consumption. Inulin or inulin‐treated serum did not stimulate platelets. In these experimental conditions some NADH disappeared, as shown by isotachophoresis. The results demonstrated that an immunological stimulus may activate a membrane‐linked cyanide‐insensitive oxygen metabolizing system.

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