Two different primate species express an identical functional MHC class I allele

The products of the highly polymorphic and variable major histocompatibility complex (MHC) class I loci play a crucial role in host defenses against infectious disease. While similar alleles have been found in closely related species, sharing of a functional MHC class I allele between two species has never been reported. Here we show that an identical functional MHC class I molecule is present in two different primate species with an approximate divergence time of 0.7 million years. Lymphocytes from the red-crested tamarin ( Saguinus geoffroyi ) expressed an MHC class I allele ( Sage-G * 01 ) that was identical in coding sequence to an MHC class I allele ( Saoe-G * 08 ) found in the cotton-top tamarin ( Saguinus oedipus ). Furthermore, influenza virus-specific cytotoxic T lymphocytes (CTLs) generated in the cotton-top tamarin killed lymphocytes expressing the influenza virus nucleoprotein (NP) from the red-crested tamarin. Since the influenza virus NP epitope is bound by Saoe-G * 08 in the cotton-top tamarin, it is likely that this molecule is functional in both species. These data provide the first evidence that functional MHC class I molecules can be maintained entirely intact in two separate species.