Human neutrophils express the interleukin-15 receptor α chain (IL-15Rα) but not the IL-9Rα component

The interleukin-15 receptor (IL-15R) is composed of at least three chains, namely gamma(c), IL-2R beta, and the recently identified IL-15R alpha, while the IL-9R complex consists of gamma(c) and a subunit designated IL-9R alpha. Our previous work and that of others have shown that human neutrophils express gamma(c) and IL-2R beta (two components shared with IL-2R) but not IL-2R alpha and that IL-15 is a neutrophil agonist, whereas IL-2 is not. In this study, using flow cytometry with a specific anti-human IL-15R alpha, we show for the first time that human neutrophils express surface IL-15R alpha. Although we previously found that IL-15 is a neutrophil agonist, our present work shows that IL-15 does not trigger superoxide production nor cell spreading onto glass. In addition, we report that human neutrophils do not respond to IL-9 with respect to the functions/responses studied, namely, superoxide production spreading onto glass, cell shape changes, phagocytosis, RNA synthesis, and apoptosis. Further, our results show that neutrophils do not express IL-9R alpha as assessed by flow cytometry with a specific anti-human IL-9R alpha antibody that stains the transfected cell line BW-h9R used as positive control. Finally, our results indicate that gamma(c) expression was not modulated and remained stable for up to 24 h when neutrophils were stimulated with all currently known "gamma(c) users," namely, IL-2, IL-4, IL-7, IL-9, and IL-15. We conclude that human neutrophils express all IL-IBR components on their surface, including IL-15R alpha, that IL-15 activates human neutrophils (as the IL-4 neutrophil agonist) by a mechanism which does not involve upregulation of gamma(c) cell surface expression, and that IL-9 is not a neutrophil agonist as demonstrated by the inability to modulate the tested functions/responses that correlate with lack of the IL-SR component, namely, IL-9R alpha. (C) 1998 Academic Press.