Simultaneous quantitation of cytokine mRNAs by reverse transcription-polymerase chain reaction using multiple internal standard cRNAs

Cytokines produced in abnormal amounts or patterns contribute to many immunologically mediated human diseases. We describe a competitive reverse transcription-polymerase chain reaction (RT-PCR) assay to measure interleukin (IL)(1)-2, IL-4, and interferon-gamma (IFN-gamma) mRNAs within the sample. Internal standard cRNAs and native cytokine mRNAs are reverse transcribed and then amplified by PCR in the same reaction tubes to control for tube-to-tube variability in these reactions. In contrast to systems that use a single multigene internal standard cRNA, this method uses separate internal standard cRNAs for IL-2, IL-4, and IFN-gamma, allowing independent dosing of the internal standards, which reduces the number of tubes processed and the amount of starting mRNA required. Internal standards are produced from cytokine cDNAs by the insertion of short segments of DNA. The same oligonucleotide primers are used to amplify internal standard and native cytokine cDNAs. Each internal standard cDNA and its matching native cytokine cDNA are amplified with equal efficiency. The RT-PCR products of the internal standards and native cytokines are distinguished by size. This technique can detect a twofold difference in mRNA levels. Examples of using this technique to measure cytokine mRNAs in peripheral blood mononuclear cells and in bronchoalveolar lavage cells are given.