IL-4 enhances IL-3 and IL-8 gene expression in a human leukemic mast cell line

We examined the capacity of interleukin (IL)-4 to induce or enhance the expression of certain cytokines in resting and activated cells of the HMC-1 human leukemic mast cell line. The HMC-1 mast cells were cultured with or without recombinant human IL-4 and then activated with the calcium ionophore ionomycin. Stimulation of non-IL-4-treated cells with ionomycin (10 microM) for periods of 30 min to 8 hr induced expression of mRNA encoding IL-3, IL-4 and IL-8 but was without effect on levels of mRNA for tumour necrosis factor (TNF)-alpha or beta-actin. Culture of the cells with IL-4 (100 ng/ml) for 24 hr led to a small increase in resting levels of mRNA for IL-3 and IL-8 but not for IL-4, TNF-alpha or beta-actin. More notably, the IL-4 treatment produced a pronounced elevation of mRNA for IL-3 and IL-8 when the cells were subsequently activated with ionomycin. The IL-4 treatment produced a negligible effect on IL-4 mRNA, and no effect on TNF-alpha or beta-actin mRNA levels in ionomycin-activated cells. Quantitation of cDNA by competitive polymerase chain reaction (PCR) revealed that the IL-4 treatment produced a sixfold increase in ionomycin-induced levels of cellular IL-3 mRNA, a fourfold increase in induced IL-8 mRNA and less than a twofold increase in induced IL-4 mRNA. The IL-4 treatment led to a 15- to 20-fold increase in ionomycin-induced secretion of IL-3 product and a doubling of induced IL-8 product. These effects of IL-4 were not associated with increased mast cell numbers. We conclude that IL-4 alone is a weak activator of IL-3 and IL-8 gene expression in mast cells, but is able to enhance activation signals in stimulated mast cells leading to transcription and secretion of these two cytokines.