Determination of cytokine production by quantitative ELISA. Open columns, IFN-gamma. Hatched columns, IL-4. Black columns, IL-5. The OD₄₀₅ values for the ELISA are shown. (A) Cytokine production by APC-depleted, purified naive CD4+ T cells after 4 days of stimulation with EpCAM-transfected CHO cells armed with 250 ng/ml bscAb EpCAM x CD3 (bscAb) and/or 500 ng/ml single-chain B7-1 construct (scB7-1). Stimulation by unarmed EpCAM-transfected CHO cells served as negative control (-). Additional controls consisted of PBMC that were stimulated for 4 days with 5 µg/ml PHA or remained unstimulated (-). (B) Cytokine production by APC-depleted, purified naive CD4+ T cells primed in the presence or absence of 100 U/ml IL-4 after 10 days of culture. Abbreviations and concentrations of constructs as in A.