Comparison of the effect that IL-2, IL-7, IL-9, and IL-15 have on Ig production by IL-4–stimulated PBMCs. PBMCs were stimulated with 200 U/mL of IL-4 without or with 10 ng/mL IL-2, IL-7, IL-9, or IL-15. IgA1, IgA2, IgE, and IgG1-4 were quantified using supernatants harvested after 12 days of culture. Results are expressed in percent of Ig increase as described in the Material and Methods and are representative of one of three experiments.