Figure 5.

CD8 mRNA levels in transitional intermediates. (A) CD3^hi thymocytes from CD4^+/L mice (CD4⁺ and CD8⁺ populations) and II⁰ CD4^+/L mice (CD4⁺CD8^intβgal^hi, CD4⁺CD8^intβgal^lo), as well as total CD4⁺CD8⁺ thymocytes from II⁰ CD4^+/L animals, were purified and analyzed by RT-PCR for their expression of CD8 mRNA. Cytoplasmic RNA was prepared, cDNA synthesized, and serial dilutions of the different cDNA samples (amount indicated above each lane as cell equivalents) were used as template for simultaneous PCR amplification using CD8 and TCR-β–specific primers. PCR products were detected by hybridization. (B) Results from five RT-PCR experiments where the amount of PCR product hybridizing to a CD8 probe was quantified, standardized with the internal TCR-β control, and normalized as fold over DP cells (defined as 1). The CD8 mRNA ratio of CD4⁺CD8^intβgal^lo to CD4⁺ CD8^intβgal^hi thymocytes is 2.76 ± 0.94.