Similarity and Difference of eosinophil activation by interleukin-5 and eotaxin

Abstract

Eosinophil infiltration is often a basic finding of inflammatory airway disease such as asthma and is mediated by a variety of soluble factors including chemokines and cytokines. Eosinophil mobilization following exposure to the chemotactic cytokines occurs via a series of event, including transient increase of calcium, the activation of mitogen-activated protein kinases, actin polymerization and rapid shape changes associated with the chemotactic responses. Given that eosinophil migration is a critical event for the pathological development of airway disease and that shape change of eosinophils is a prerequisite for this event, it is of pivotal importance to understand the underlying mechanism by which eosinophil shape change occurs. In this study we examined the abilities of a number of cytokines to induce eosinophil shape change and the signaling pathways for eosinophils shape change by interleukin(IL)-5 and eotaxin, the most prominent cytokine/ chemokine regulating eosinophil locomotion and function, with a gated autofluorescence/ forward scatter (GAFS) assay. Either interferon-γ (IFN-γ) or IL-4 alone caused to decrease eosinophil shape change while tumor necrosis factor-α (TNF-α) and IL-6 augmented. Further, the pretreatment with IFN-γ significantly inhibited IL-5-induced shape change of eosinophils. The inhibitory effect of IFN- on eosinophil shape change was abrogated by cycloheximide, suggesting the requirement of protein synthesis. Others including IL-1β, IL-10 and IL-13 had minor effect on shape change either alone or in combination with IL-5. Eotaxin and IL-5 are the most potent in eliciting shape change with maximum values at 10 and 60 min, respectively, exhibiting more rapid kinetics for eotaxin than IL-5. The pharmacologic inhibitors of MEK and p38 blocked both eotaxin- and IL-5-induced eosinophil shape change in a dose-dependent manner. In addition, Ca2+ chelation and the PKA and PLC inhibition also sharply reduced the shape change. In contrast, the inhibition of PTK and PKA resulted in slight reduction of the shape change only at a high concentration. Jak2 inhibition did not alter the shape change. Treatment with PKC inhibitors such as staurosporin and GF109203X, surprisingly enough, resulted in reduction of eosinophil shape change by IL-5 but not eotaxin. Taken together there is a distinct signaling pathway that is not shared by the two eosinophil-active cytokines although eosinophil shape changes by the two are considerably overlapped.