Quantitative analysis of IL-4 and G3PDH mRNA by competitive PCR. CD4⁺ T cells were stimulated with anti-CD3 MoAb and CD32/B7.1-transfected L cells in the presence of control mouse IgG2a or anti-OX40 MoAb (clone 315; 5 μg/mL) for 48 hours. Total RNAs of both groups of cells were prepared, and cDNA was synthesized. Quantitative PCR was performed in the presence of a twofold dilution of competitive internal standards (PCR MIMICs) of IL-4 (A) and G3PDH (B). The mean histogram of each band was analyzed by computer imaging. The ratio of target to competitors was plotted against the reciprocal of the concentrations of competitors added to the PCR reaction in log scale (C and D). Data were derived from RNA of (○) control IgG2a-treated cells and (•) anti-OX40 MoAb-treated cells.