The Chemoattractant Properties of Interleukin-4

Abstract

Interleukin-4 (IL-4) is an important cytokine in B-cell differentiation and has been recently found to have a role in the selective recruitment of eosinophils via up-regulation of V-CAM. We have studied the effects of IL-4 in vitro as a chemoattractant for both eosinophils and neutrophils. Neutrophils were isolated on Ficoll-Hypaque to a purity of 98%, while eosinophils from atopic donors were isolated on discontinuous Percoll gradients to a purity of 68 ± 8%. Chemotaxis was assayed in multiwell modified micro Boyden chambers using polycarbonate filters with 5 µm and 8 gm pore size respectively. Chambers were incubated for one hour at 37° C, and filters removed, fixed and stained with Haema­Gurr. 10 high power fields were counted per duplicate experiment and results expressed as cells per high power field (cells/HPF). The mean ± SEM of 5 separate experiments are presented. Concentrations of IL-4 ranging from 0.1-1000 ng/ml were tested. Neutrophils demonstrated a dose-response curve with an optimum response of 63.4 ± 14.5 cells/HPF at 10 ng/ml which was significantly different to the response to buffer of 30.0 ± 9.2 cells/HPF (p=0.032). FMLP (10^-8M) as positive control gave a response of 121 ± 23.6 cells/HPF. Eosinophils also showed a dose-response curve with an optimum response at 100 ng/ml IL-4 of 9.9 ± 1.86 cells/HPF compared to buffer response of 4.7 ± 1.1 cells/HPF (p=0.055). The peak response to PAF (10^-7M) was 12.6 ± 2.5 cells/HPF. We conclude that IL-4 appears to be a chemoattractant for both neutrophils and eosinophils.