Eur. J. Imrnunol. 1993. 23: 1687-1692 IL-9 promotes zyxwv IgE production by human B lymphocytes 1687 Bernard Dugas., Jean Christophe Renauld.0, JBrome Phne., Jean Yves BonnefoyA, Corinne Peti-Fkkre., Pierre Braquet., Jean Bousquet., Jacques Van Snick. and Jean Michel Mencia-Huerta. INSERM zyxwvutsr CJF 92-10., Montpellier, Ludwig Institute for Cancer Research., Brussels, Glaxo Institute for Molecular BiologyA, Genkve, Institut Henri Beaufour., Les Ulis Interleukin-9 potentiates the interleukin-4-induced immunoglobulin (IgG, IgM and IgE) production by normal human B lymphocytes IgE production by normal peripheral blood lymphocytes (PBL) is known to be triggered upon stimulation by interleukin (1L)-4. In the present study we showed that IL-9, another T cell-derived cytokine, markedly potentiated IgE production induced by suboptimal doses of IL-4,whereas no effect of IL-9 was observed in the absence of IL-4.The potentiating effect of IL-9 appeared to be associated with the increased frequency of IgE-producing cells, as revealed by a specific ELISA-spot assay. Under the same experimental conditions, IL-9 also enhanced the IL-Cinduced IgG production but did not elicit IgM production. However, IL-9 did not amplify the IL-Cdependent expression of membrane-bound and soluble low affinity receptor for IgE (CD23). IL-Cinduced IgE production was also potentiated by IL-6 but not by tumor necrosis factor-a and IL-lp. The possibility that the activity of IL-9 was mediated by IL-6 released from accessory cells was excluded by the observations that monocyte depletion did not abolish the effect of IL-9 and that IL-9 was still active on fluorescence-assisted cell sorted CD20+ B lymphocytes co-cultured with irradiated murine EL4 cells. In addition, IL-9 was shown to potentiate the IL-Cinduced IgG and IgM production by normal human B lymphocytes preactivated with Staphylococcus zyx aureus Cowan strain. Taken together, these data suggest that IL-9 plays a regulatory role in the IL-Cdependent immunoglobulin production. 1 Introduction The glycoprotein IL-9/P40 was first described as a factor supporting the growth of someT cell lines but not of freshly isolated T lymphocytes [l, 21. Independently, a new factor active on mucosal mast cell lines was described and termed mast cell enhancing activity (MEA) [3, 41. This factor, which also stimulates the production of IL-6 [5] by IL- 3-dependent mast cell lines was subsequently shown to be identical to P40 and is now referenced as IL-9 [l, 61. The human protein, first identified as a growth factor for a megakaryoblastic leukemic cell line zyxwvuts [7], is produced by activated peripheral T lymphocytes [8,9] and was also found to induce the survival of some T cell lines [lo] and to promote erythroid burst formation from hematopoietic precursors [ll]. Mast cells and IgE production, two key elements in type I hypersensitivity reactions [12], have shown to be stimulated by IL-4, another T cell-derived cytokine. Indeed, IL-4 is a cytokine produced by T lym- [I 115691 zyxwvu 0 Research assistant with the Fonds National de la Recherche Scientifique, Belgium. zyxwvutsrq Correspondence: Bernard Dugas, INSERMICJF 92-10, HBpital Arnaud de Villeneuve, 555 route de Ganges, F-34059 Montpellier, France (Fax: 67042708) Abbreviations: LME: L-Leucyl methyl ester zyxwvut CD23: Low-affin- ity receptor for IgE Key words:Interleukin-4 I Interleukin-9 I IgE I B lymphocytes phocytes and mast cells [ 131 that induces IgE production by normal human B lymphocytes [14-171. In addition, IL-4 induces the low-affinity IgE receptor (CD23) expression on, and release from,various cell types [17-191, whose role in the regulation of IgE production in human has been suggested [20]. The activity of IL-9 on mast cell lines suggested that this factor could also be involved in the regulation of allergic reactions and especially in the regu- lation of IgE-dependent mechanisms. The present report indicates that IL-9 potentiates the IL-Cinduced immunoglobulin (IgG , IgM and IgE) produc- tion by normal human peripheral B lymphocytes. 2 Materials and methods 2.1 Cytokines and reagents IL-4, IL-lP,TNF-a and IL-6 and the rabbit anti-human IL-6 antibody were purchased from Biotrans (Los Angeles, CA), recombinant human IL-9 was prepared as previously described [lo, 211; 150 pg/ml IL-9 correspond approxima- tively t o 1 U/ml as measured on IL-9-responsive Mo7E cells. All culture reagents were from Flow labs (Irvine, Scotland). 2.2 Cell preparations and cultures Peripheral blood lymphocytes (PBL) were isolated from heparinized blood from healthy donors. Mononuclear cells were separated by centrifugation on Ficoll/Hypaque (Phar- macia, Uppsala, Sweden) gradients.To remove monocytes, PBL were incubated for 45 min at room temperature with 0 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1993 0014-29801Y310707-1687$10.00 + .2510