Lymphocyte differentiation in sea bass thymus: CD4 and CD8-α gene expression studies.

Different developmental stages (from eggs to 1-year-old juveniles) of the teleost fish Dicentrarchus labrax (L.) were assayed for CD4 gene expression. RT-PCR revealed the appearance of CD4 transcripts in postlarvae from 51 days post-hatching (dph). This finding overlaps the first detection of CD8-alpha mRNA. Real-time PCR with specific primers quantified CD4, CD8-alpha and TCR-beta transcripts in larvae and postlarvae (25, 51, 75 and 92 dph) and 1-year-old thymus. At 92 dph, TcR-beta and CD8-alpha transcripts were significantly higher (P<0.001) than in previous stages, as CD4 transcripts compared with 51 dph (P<0.01). High levels of TCR-beta and CD8-alpha transcripts were found in the thymus, while CD4 transcripts were lower (P