Interleukin-9 enhances interleukin-5 receptor expression, differentiation,and survival of human eosinophils

Interleukin-8 (IL-9) has been implicated in the pathogenesis of allergic di sorders. To examine the interaction between IL-9 and eosinophils, we evalua ted mature peripheral blood eosinophils for their expression of the specifi c alpha-subunit of the IL-9 receptor (IL-9R-alpha), The expression of IL-9R -alpha by human eosinophils was detected at the messenger RNA (mRNA) and pr otein levels by reverse transcriptase-polymerase chain reaction (RT-PCR), f low cytometry, and immunocytochemical analysis, respectively. Functional an alyses demonstrated that recombinant human (rh)IL-9 inhibited in vitro peri pheral blood human eosinophil apoptosis in a concentration-dependent manner . We then examined the role of IL-9 in eosinophil differentiation using the human cord blood CD34(+) cells and human promyelocytic leukemia cells (HL- 60), The addition of IL-9 to CD34(+) cells cultured in IL-3 and IL-5 enhanc ed eosinophil development, and IL-9 alone induced the expression of IL5R-al pha. IL-9 also up-regulated the IL-5R-alpha chain cell surface expression d uring terminal eosinophil differentiation of the HL-60 cell line. Our findi ngs suggest that IL-9 may potentiate in vivo eosinophil function by increas ing their survival and IL-5-mediated differentiation and maturation. Taken together, these results suggest a mechanism by which IL-9 potentiates airwa y and tissue eosinophilia. (Blood, 2000; 96:2163-2171) (C) 2000 by The Amer ican Society of Hematology.