Dose-dependent inhibition by IL-4 of IL-6– and TNF-α–induced mast cell development. Mouse spleen cells were cultured with rIL-6 and rTNF-α in the presence of various doses of rIL-4. Mast cell number (A) and histamine quantity (B) per culture were determined on day 12. * P < .01, ** P < .05 compared with data without adding rIL-4.