Effect of interleukin 8 in meconium on in-vitro neutrophil chemotaxis

Background Pneumonitis, characterised by large numbers of neutrophils in the lung, is an important feature of the meconium aspiration syndrome. The mechanism underlying the neutrophil influx is not known. We have investigated whether meconium has chemotactic activity and whether such activity is related to the presence of interleukin 8. Methods The chemotactic activity of meconium on neutrophils from newborn infants was assessed in a Boyden-chamber assay. Interleukin 8 and formyl-methionyl-leucyl-phenylalanine (f-MLP) served as positive controls. Inhibition of chemotaxis was assessed with monoclonal antibody to interleukin 8. The interleukin-8 concentration was measured by ELISA. Findings Sterile meconium suspension from seven unrelated newborn babies increased migration of neutrophils from neonates in comparison with random migration (79, 72, 70, 50, 58, 88 mu m vs 46 mu m; p<0,001). This effect was greatest at a meconium concentration of 5 g/L, although differences between samples from individual babies were observed. Interleukin 8 was present in all meconium suspensions (480-3980 ng/L). Anti-interleukin-8 inhibited neutrophil migration. Interpretation Interleukin 8 is present in meconium and it induces chemotaxis of neutrophils in vitro. This mechanism may have a role in the pathogenesis of pneumonitis in meconium aspiration syndrome.