Time course for mast cell development induced by IL-6 and TNF-α. rIL-6 or rTNF-α (10 ng/mL) was added to the cultures on day 0, 2, 4, 6, or 8. Control was set up without addition of the cytokines. Mast cell number (A) and histamine quantity (B) per culture were determined on day 12.