Homotypic aggregation of cultured human mast cells induced by IL-4. Cultured human mast cells were grown from CB MNCs in the presence of SCF (100 ng/mL) and IL-6 (80 ng/mL) for 10 weeks. Cells were then incubated for 10 days without (A) or with (B) IL-4 (10 ng/mL) in the presence of SCF and IL-6. Half of the media was changed on the fifth day of the culture. This experiment has been repeated five times with similar results.