Immunoassay for IFN-γ and IL-2 Concentrations of IFN-γ and IL-2 in culture supernatants of CD4+ T cells were measured in duplicate by the quantitative sandwich ELISA using cytokine-specific capture with biotinylated detection mAb and recombinant cytokine proteins (all from Becton Dickinson), according to the manufacturer's protocol. The detection limits for IFN-γ and IL-2 were 15 pg/ml.