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Effects of low concentrations of arachidonic acid derived mediators on the membrane potential and respiratory burst responses of human neutrophils as assessed by flow cytometry

Summary— Hypaque‐Ficoll purified (95%) neutrophils (PMN) from normal healthy subjects were assessed for FMLP‐elicited membrane potential (Δφ) responses and dichlorofluorescein (DCF) fluoresence (a measure of intracellular hydrogen peroxide production) using flow cytometry and appropriate fluorescent probes. Superoxide (O2) production was measured spectrophotometrically as the superoxide dismustase‐inhibitable reduction of cytochrome C. The modulatory effects of dilute solutions of the arachidonic acid‐derived inflammatory mediators LTB4, LTC4, LTD4, PGE1, PGE2 and PGF2α (10−9 – 10−5 M) were assessed in these systems. While LTB4 enhanced the proportion of cells depolarizing to the chemoattractant N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) 2–3 × with a maximum effect in the 10−9 – 10−8 M range, LTC4 and LTD4 showed no such enhancement except at high concentrations (10−6 M). Unlike LTB4, LTC4 and LTD4 were unable to enhance FMLP mediated PMN O2 or DCF responses at any concentration tested, implying a divergence between the effects of the leukotrienes on membrane potential and oxidant responses. Pre‐incubation of PMN with prostaglandins E1 or E2 led to a dose dependent inhibition of the proportion of depolarizing PMN in response to FMLP; PGF2α did not show such an effect. The present data indicate that LTB4, in addition to being a powerful direct neutrophil activator, may act in a priming capacity by increasing the proportion of subsequently FMLP responsive cells, while PGE's inhibit. These modulatory effects appear relatively specific for LTB4 and the E‐series prostaglandins.