Cloning of feline cDNA encoding the cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) is a CD28 homologue which down-modulate T cell responses rather than augment them. To investigate its biological role in feline immune system, we cloned and sequenced full-length feline CTLA-4 (fCTLA-4) cDNA by RT-PCR from pokeweed mitogen stimulated peripheral blood lymphocytes. The fCTLA-4 contains an open reading frame of 669 nucleotides, coding for a polypeptide of 223 amino acids. The predicted fCTLA-4 amino acids sequence shows the homology of 86.6%, 87.0%, and 76.2% with human, bovine, and murine molecules respectively. The hexapeptide motif (MYPPPY) within the extra-cellular domain of CTLA-4 molecule, which is believed to be responsible for interaction with the B7 family members, is completely conserved in all the species.