A parallel signal‐transduction pathway for eotaxin‐ and interleukin‐5‐induced eosinophil shape change

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Abstract
Summary: Interleukin‐5 (IL‐5) and eotaxin are the most important cytokines/chemokines responsible for regulating eosinophil locomotion and are known to play a co‐operative role in the selective recruitment of eosinophils to inflamed tissues. Following exposure to chemoattractants, eosinophils undergo a series of events, including reorganization of actin filaments and subsequent rapid shape changes, culminating in chemotaxis. In this study we examined the signalling pathways for eosinophil shape change regulated by eotaxin and IL‐5, primarily using a gated autofluorescence/forward‐scatter assay. Eotaxin and IL‐5 were able to elicit shape change with peaks at 10 and 60 min, respectively, and IL‐5 triggered the shape change more efficiently than eotaxin. The pharmacological inhibitors of mitogen‐activated protein kinase (MAP kinase) and p38 blocked both eotaxin‐ and IL‐5‐induced eosinophil shape change in a dose‐dependent manner. In addition, depletion of intracellular Ca2+ and inhibition of protein kinase A (PKA) strongly reduced eosinophil shape change. In contrast, even when used at high concentrations, protein tyrosine kinase (PTK) inhibitors caused only a slight reduction in the ability to change shape. However, treatment with protein kinase C (PKC) inhibitors, such as GF109203X and staurosporine, resulted in a striking inhibition of eosinophil shape change by IL‐5, but not eotaxin. Data from the inhibition of activation and chemotaxis of the extracellular signal‐regulated kinases (ERK1/2) by the PKC inhibitors were also consistent with findings from the experiments on shape change. Collectively, two eosinophil‐selective cytokines/chemokines probably regulate eosinophil shape change via a largely overlapping signalling pathway, with involvement of PKC restricted to the IL‐5 signal alone.

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