Molecular cloning of the feline CD8β-chain

Human, mouse and rat CD8 have been described as being disulphide-linked heterodimers of α and β chains. More recently the chicken α and β chains were described. In the bovine and feline immune system only the α-chain was reported. In this study we have cloned and determined the nucleotide sequence of a cDNA encoding the β-chain of the feline T-cell surface antigen CD8. Using a nested polymerase chain reaction (PCR) and two primer pairs designed from the human CD8β cDNA nucleotide sequence, we amplified a 430 base pair fragment from a feline thymus cDNA library which was used as a probe for screening the feline library at high stringency. After three rounds of screening, five clones were isolated. A clone, named FTb-6, containing a 3.8 kilobase pair insert was mapped, sequenced and compared with the published sequences of the genes encoding the human, mouse, rat and avian CD8β. We have determined the primary structure of the feline CD8β. The feline CD8β has an open reading frame, 630 nucleotides in length encoding a protein with 210 amino acid residues and its composition showed that the feline molecule is a member of the immunoglobulin gene super family.