Molecular cloning and sequencing of feline CD56 (N‐CAM)

We isolated feline CD56 cDNA to investigate the primary structure of CD56 of feline leukocytes. Sequencing analysis revealed that an open reading frame (2538 bp) encoded a homologue of a 140-kDa isoform of CD56. The predicted amino acid sequence showed 97.3% homology with that of humans. Natural killer (NK) cells exhibit MHC-unrestricted cytotoxicity and play important roles in the immune system, where the NK cells recognize and kill certain tumour cells and virus-infected cells. CD56 (neural cell adhesion molecule: N-CAM), a cell surface antigen, has been used as a marker of NK cells in humans (Lanier et al., 1989). Several isoforms of CD56 have been identified: the 140- and 180-kDa forms are expressed as transmembrane proteins, whereas the 120-kDa form is a phosphatidylinositol-glycan anchored protein (Cunningham et al., 1987). Differences amongst these polypeptides are found mainly within the transmembrane and cytoplasmic domains and arise from alternative mRNA splicing from a single gene.