Molecular characterization of guinea - pig (Cavia porcellus) CD8alpha and CD8beta cDNA

CD8 is expressed on cytotoxic T cells (CTL) and functions as a coreceptor for recognition of major histocompatibility complex (MHC) class I peptide complexes by the T-cell receptor (TCR). The CD8 molecule consists of two subunits (alpha and beta) and exists either as a heterodimer (alphabeta) or a homodimer (alphaalpha). We report the cloning of full-length cDNAs of guinea pig CD8alpha and CD8beta. The deduced amino acid sequence of CD8alpha and CD8beta reveals characteristic structural features including a signal peptide, an immunoglobulin (Ig) variable-like region, hinge region, transmembrane, and cytoplasmic domains. In addition to the full-length cDNA, a splice variant of CD8beta cDNA was observed, suggesting splicing events as reported for human CD8beta. The sequence homology of guinea pig CD8 indicates greater homology to human, canine, and feline counterparts than to rodent CD8. As the guinea pig serves as an ideal non-primate animal model to several human infectious diseases, such as syphilis, tuberculosis, and chlamydial genital and ocular infection, the CD8 sequence information provides a necessary molecular tool for studying the cell-mediated immune response.