EFFECT OF LIPOXINS AND OTHER EICOSANOIDS ON PHAGOCYTOSIS AND INTRACELLULAR CALCIUM MOBILIZATION IN RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) LEUKOCYTES

Rainbow trout (Oncorhynchus mykiss) macrophages generated lipoxin (LX) A4, LXA5, leukotriene (LT) B4, LTB5 and 12-hydroxyeicosatetraenoic ac id (12-HETE) during the phagocytosis of zymosan and Escherichia coli, but not of the yeast Saccharomyces cerevisiae. Prostaglandin (PG) E2 w as also detected in supernatants from macrophages incubated with eithe r zymosan or calcium ionophore A23187. LXA, (10(-8)-10(6) M) and LTB4 (10(-9)-10(-7) M) provoked rapid and transient dose-dependent increase s in intracellular calcium ([Ca]i) concentrations in leukocyte suspens ions containing 40-60% macrophages. EC50 values were 14.9 and 1.2 nM, respectively. PGE2 and 12-HETE had no effect on [Ca]i at concentration s up to 30 muM. PGE2 and 12-HETE (10(-5)-10(-10) M) enhanced the in vi tro phagocytosis of yeast test particles by trout macrophages, whereas LXA4 and LTB4 had no demonstrable effect on the responses of these ce lls at concentrations up to 10(-5) M. In conclusion, the processes inv olved in trout macrophage stimulation are complex but involve generati on of both cyclooxygenase and lipoxygenase products. The increase in [ Ca]i caused by LXA4 and LTB4 may form part of the chemotactic transduc tion mechanism that recruits granulocytes and macrophages to sites of inflammation. The effects of eicosanoids on phagocytosis appear to be independent of changes in [Ca]i.