COMPARATIVE DIFFERENCES AND COMBINED EFFECTS OF INTERLEUKIN-8, LEUKOTRIENE B-4, AND PLATELET-ACTIVATING-FACTOR ON NEUTROPHIL CHEMOTAXIS OF THE NEWBORN

IL-8, leukotriene B-4 (LTB(4)), and platelet-activating factor (PAF) are potent neutrophil chemoattractants that have been identified in inflammatory conditions of the newborn such as chronic lung disease of extreme prematurity. The aims of this study were to determine the relative potency and combined effects of these mediators on chemotaxis of polymorphonuclear leukocytes (PMN) from the newborn and to compare the effect of combining all three mediators on chemotaxis of PMN from newborns and adults. Neutrophils were isolated from cord blood (n = 17) or healthy adults (n = 4) and incubated in a 3-tier, 48-well chemotaxis chamber. For PMN from newborns, using chemoattractant concentrations ranging from 0.01 to 100 nM, we found that there were significant differences in potency: IL-8 > LTB(4) > PAF. Migration to each of these mediators was almost completely due to chemotaxis as opposed to chemokinesis. At submaximal chemotaxis, using equally effective doses of IL-8 (0.2 nM), LTB(4) (1.0 nM), and PAF (10 nM), the combination of all three mediators increased chemotaxis 2.4-fold above the average individual responses. Further studies indicated this increase in chemotaxis was due to the combination of IL-8 and PAF or IL-8 and LTB(4); but there was no increase in chemotaxis when PAF and LTB(4) were combined. The combination of all three submaximal doses of chemoattractants resulted in PMN chemotaxis that was still 36% of the adult response. We conclude that for neutrophils from the newborn: 1) IL-8 is a potent stimulus that has additive effects on chemotaxis in combination with either LTB(4) or PAF, 2) the combination of LTB(4) and PAF did not have an additive effect on chemotaxis, and 3) in spite of enhanced chemotaxis by more than one stimuli, the response is still significantly lower than for neutrophils from adults.