Identification and molecular characterization of CD4 genes in brown trout (Salmo trutta)

CD4⁺ cells are vital in coordinating the immune response against pathogens. In the present study, three different CD4 homologs, namely, CD4-1, CD4-2a, and CD4-2b were identified and characterized. Further, their basal expression levels in different brown trout (Salmo trutta) tissues were also investigated. CD4-1 was 1473 nucleotides long, with an open reading frame (ORF) encoding 490 amino acids with four immunoglobulin superfamily-like domains. CD4-2a and CD4-2b like genes were 945 and 999 nucleotides long containing ORFs with 313 and 331 amino acids, respectively. The brown trout CD4-1 protein sequence demonstrated a 95% and 89% identity with Atlantic salmon and rainbow trout CD4-1 genes, respectively. On the other hand, brown trout CD4-2a and CD4-2b protein sequences presented an identity of 84% and 97.7% with rainbow trout and Atlantic salmon, respectively. The basal expression levels of the identified brown trout CD4-genes were investigated, which were higher in thymus, spleen, and head kidney than in those the gills, liver, intestine, heart, and brain tissues.