IL-4 dependent hIgE secretion. Human PBMC were repeatedly isolated from two different donors and incubated in the absence (control; n = 10) or presence of IL-4 (50 ng/ml; n = 10). After 14 days the hIgE level was determined in the supernatant. For in vivo stimulation of hIgE secretion in NOD-scid IL2R γnull mice engrafted with hPBMC from the same donors the animals were treated on five consecutive days (8–12) with 10 μg IL-4, dissolved in PBS (IL-4, n = 10) or 0.5% methylcellulose, 0.05% TWEEN 80 (IL-4 + Methylcellulose; n = 12). Administration of 0.5% methylcellulose, 0.05% TWEEN 80, PBS (Methylcellulose, n = 4) served as control. IgE levels were significantly different in the three in vivo groups (Kruskal Wallis test, p = 0.015).