Quantification of IL-12 p40 mRNA. (A) A IL-12 p40 cDNA scale constituted from gel-purified, quantified, and serially diluted PCR product was amplified. PCR products were sampled from every well at the indicated cycle and submitted to colorimetric detection as described in the Materials and Methods. (B) For each indicated cycle, the linear region of the curve (optical density versus standard cDNA amount) was used to estimate experimental cDNA amount (eg, cycles 24 and 36 and 2 experimental samples at 0.05 and 1.4 fg ).