Molecular characterization and immune responses of T cell receptors and CD4 in spotted seabass (Lateolabrax maculatus)

• First molecular characterization of TCRα, TCRβ, TCRγ, TCRδ, and CD4–2 genes in spotted seabass ( Lateolabrax maculatus ). • Constitutive expression profiles of TCRα, TCRβ, TCRγ, TCRδ, CD4–1, and CD4–2 transcripts analyzed across major tissues. • Dynamic transcriptional responses of four TCRs and two CD4s assessed in head kidney, spleen, gill, and intestine following immune challenge with LPS, Poly (I:C), and Edwardsiella tarda . • In vitro modulation of TCRs and CD4s expression quantified in head kidney primary leukocytes stimulated with LPS or Poly (I:C). T cell receptors (TCRs) and the CD4 receptor are pivotal for T cell-mediated immunity, yet their characterization in teleost fish remains limited. To elucidate their roles in spotted seabass ( Lateolabrax maculatus ), we molecularly cloned and characterized the genes encoding TCRα ( Lm TCRα), TCRβ ( Lm TCRβ), TCRγ ( Lm TCRγ), TCRδ ( Lm TCRδ), and CD4–2 ( Lm CD4–2). The open reading frames (ORFs) of Lm TCRα, Lm TCRβ, TCRγ, Lm TCRδ, and Lm CD4–2 were 759 bp, 888 bp, 933 bp, 792 bp, and 900 bp in length, encoding the proteins of 252, 295, 310, 263, and 299 amino acid residues, respectively. Multiple sequence alignment and phylogenetic analysis confirmed conserved structural motifs and revealed clustering with orthologs from other fish species. Quantitative real-time PCR (qPCR) analysis demonstrated predominant constitutive expression of Lm TCRα, Lm TCRβ, Lm TCRγ, Lm TCRδ, Lm CD4–1, and Lm CD4–2 transcripts in head kidney (HK), spleen, and gills of healthy fish. Furthermore, expression of these genes was significantly modulated in vivo (HK, spleen, gills, intestines) and in vitro (primary HK leukocytes) following challenge with lipopolysaccharide (LPS), polyinosinic:polycytidylic acid [Poly (I:C)], or Edwardsiella tarda . These findings establish the involvement of Lm TCRα, Lm TCRβ, Lm TCRγ, Lm TCRδ, Lm CD4–1, and Lm CD4–2 in the immune response of spotted seabass and provide a foundation for investigating teleost cell-mediated immune defense mechanisms.