RT-PCR analysis of selected genes in four cell groups. Quantitative RT-PCR was performed in duplicate using cDNA (equivalent of 10 ng total RNA) and already-developed TaqMan gene expression assays (Applied Biosystems) on the ABI 7900 HT Fast Real-Time PCR System. Data were normalized based on 18srRNA and GAPDH expression. The mean expression level for naïve CD8+ T cells was artificially scaled to one for each tested gene. Data are presented as mean ± standard deviation.