The generation and cellular distribution of leukotriene C₄ in human eosinophils stimulated by unopsonized zymosan and glucan particles

Human eosinophils (EOSs) stimulated under optimal conditions with 5 × 10⁸ unopsonized zymosan particles at 37 °C for 30 minutes produced an average total immunoreactive leukotriene (LT) C₄ of 1.6 ng per 10⁶ EOSs, and 30% to 60% of the generated product remained cell associated. The dose-response characteristics of zymosan-induced LTC₄ generation were different from those of phagocytosis, suggesting that the two events were independent. Pretreatment of EOSs with 10^-8 mol/L of formyl-methionyl-leucyl-phenylalanine for 30 minutes led to a twofold to fivefold augmentation of LTC₄ generation by cells subsequently activated by unopsonized zymosan. Optimal EOS activation with 1 μmol/L of the calcium ionophore A23187 at 37 °C for 15 minutes produced more than 100 times greater quantities of LTC₄ than with zymosan. The amount of immunoreactive LTC₄ that remained cell associated after calcium ionophore A23187 stimulation reached a maximum after 5 minutes and then declined. Of the relatively small amount generated in the first minute, 71% was cell associated, but this figure declined to 9% after 15 minutes, by which time there had been a redistribution of the LTC₄ to the supernatant. Inflammatory leukocytes may respond to zymosan because the cells recognize either one or both of its major polysaccharide components, glucan and mannan. Glucan, but not mannan, stimulated EOSs to generate LTC₄ in a dose- and time-dependent manner. Under optimal conditions, there was no significant difference in the total quantities of LTC₄ elaborated by EOSs stimulated by glucan and by unopsonized zymosan. This suggests that zymosan may induce leukotriene generation in the human EOS through a glucan recognition mechanism.