CCR3-mediated degranulation and eosinophil-associated RNases secretion from murine eosinophils; capacity of intact cells and free granules (86.21)

Abstract

Abstract Piecemeal degranulation (PMD), in which intact eosinophils completely or partially empty granules and selectively secrete performed mediators, is the principal mechanism for human eosinophil degranulation. Unlike extensively studied human eosinophils, both the capacity and mechanisms underlying eosinophil degranulation responses of murine eosinophils have been poorly investigated and remain controversial. We applied a new methodology to detect degranulation by measuring secretion of eosinophil-associated RNases (mEARs) and found that murine eosinophils “degranulated” following stimulation with CCL11 and CCL24, as detected by an increase in RNase A and EPO activities in cell supernatants. TEM revealed signs of PMD including significant increase in the number of emptying granules. CCL11 and CCL24-mediated mouse eosinophil degranulation was Gαi and PI3K-dependent. Moreover, intact beta 1 and 2 integrins as well as dynamic cytoskeleton are required for this PMD. Unexpectedly, we found that inhibition of Rho-GTPase kinase increases PMD. Moreover, cell-free granules purified from mouse eosinophils were found to express functional CCR3 and secreted mEARs as well as EPO in response to CCL11, suggesting a unique mechanism of degranulation in cell-free context. Collectively, these data demonstrate that murine eosinophils undergo PMD in response to physiological stimulation with CCL11 and CCL24, findings that are pertinent to murine models of eosinophil-associated diseases.