Neutrophils are potent contributors to the lung pathophysiological changes occurring in allergic airway
inflammation, which typically involve T helper type 2 (Th2)
cytokine overexpression. We have previously reported that equine pulmonary endothelial cells are activated by the Th2
cytokine IL-4 and express
chemotactic factors for neutrophils after stimulation. We have further explored the possible mechanisms linking Th2-driven
inflammation and neutrophilia by studying the effects of recombinant equine
IL-4, a prototypical Th2
cytokine, on peripheral blood neutrophils (PBN) isolated from normal animals and from horses with asthmatic airway
inflammation (equine heaves). We found that
IL-4 induced morphological changes in PBN, dose- and time-dependent expression of
IL-8 mRNA, as well as the release of
chemotactic factors for neutrophils in culture supernatants. Also,
IL-4 induced a mixed inflammatory response in PBN from control and asthmatic-animals with increased expression of proinflammatory
IL-8 and TNF-α but a marked inhibition of IL-1β.
IL-4 type I receptor (IL-4Rα) and CD23 (FcεRII) expression were also upregulated by
IL-4. Importantly, disease as well as chronic antigenic exposure modified gene expression by PBN. Finally, we found that activation of equine neutrophils with
IL-4 involved STAT6 phosphorylation and
p38 MAPK and
phosphatidylinositol 3-kinase (PI3K); the pharmacological inhibitors,
SB-203580 and
LY-294002, respectively, significantly reversed IL-4-induced gene modulation in PBN. Overall, results from this study add to the link between Th2-driven
inflammation and neutrophilia in the equine model and further extend the characterization of
IL-4 effects on neutrophils.