Sandwich ELISA analysis of serial diluted mouse IL-4 recombinant protein (375, 75, 15 and 0 pg/ml, 50 ul per well) using GTX15641 IL4 antibody [1D11] (coating antibody) at 2 μg/ml and HRP-conjugated rat anti-mouse IL-4 antibody (detecting antibody) at 0.4 μg/ml