Isolation, identification and expression analysis of PD-1 gene in Tupaia belangeri

Programmed cell death 1 (PD-1) is an inhibitory receptor that belongs to the immunoglobulin (Ig) superfamily. Numerous studies have demonstrated that PD-1 expression can be induced in activated T lymphocytes, NKT cells, B lymphocytes and monocytes and play a critical role in the pathogenesis of chronic infections. Tupaia belangeri (tree shrew) represents an excellent model for some of the major human infectious diseases such as hepatitis B virus infection. To fully utilize tree shrew as a host immune response model to infectious diseases, tree shrew PD-1 was isolated. Full-length tree shrew PD-1 cDNA was cloned from spleen of tree shrew by rapid amplification of cDNA end-PCR (RACE-PCR). Sequence analysis revealed that the open reading frame (ORF) of tree shrew PD-1 cDNA encoded a predicted transmembrane protein of 242 amino acids with high homology with humans, primates and rodents. Expression of PD-1 in tree shrew was detected in spleen but not in other organs by RT-PCR. Stimulation of freshly isolated tree shrew peripheral blood monouclear cells(PBMCs) with PMA and ionomycin increased the expression of PD-1 mRNA. Our results may provide a foundation for future exploration of tree shrew immune function.