Expression of IL-4 by stimulated human peripheral blood mononuclear cells (PBMC). Human PBMC were stimulated with soluble anti-human CD3 antibody (1 µg/ml; Cat. No. 555329), recombinant human IL-2 (10 ng/ml, Cat. No. 554603) and IL-4 (20 ng/ml; Cat. No. 554605) for 2 days. The cells were subsequently cultured in medium containing recombinant human IL-2 and recombinant human IL-4 for 3 days. Finally, the cells were harvested and stimulated for 6 h with PMA (Sigma, Cat. No. P-8139) and calcium ionophore A23187 (Sigma) in the presence of 2 µM GolgiStop™ (Cat. No. 554724). The cells were harvested, stained with PE-Cy™5 -anti CD4 (Cat. No. 555348), fixed, permeabilized, and subsequently stained with 0.05 µg of PE-rat anti-human IL-4 antibody (PE-MP4-25D2, Cat. No. 554485) by using Pharmingen's staining protocol (left panel). To demonstrate specificity of staining, the binding of PE-MP4-25D2 antibody was blocked by preincubation of the fixed/permeabilized cells with unlabeled MP4-25D2 antibody (2.5 µg, Cat. No. 554482; right panel) prior to staining. The quadrant markers for the bivariate dot plot were set based on the autofluorescence controls and verified using unlabeled antibody blocking controls.