Figure 2. Determination of the exponential cycle of amplification. Semiquantitative reverse transcription–polymerase chain reaction (RT–PCR) mixtures were taken for five alternating cycles starting at cycles 18, 21, 24, 27, and 30 for A: beta 2 microglobulin (B2M), B: superoxide dismutase 1 (SOD1), C: dual-specificity phosphatase 1 (DUSP1), and D: transforming growth factor, beta 1 (TGF-B1). Cycle 24 was selected as an exponential cycle.