Molecular cloning and expression analysis of bovine programmed death‐1

Recent work has shown that PD‐1, an immune inhibitory receptor, is involved in mechanisms for down‐regulating immune responses during tumor progression or chronic viral infection. However, in the case of bovine diseases, there have been no reports on this molecule due to lack of information about bovine PD‐1. In this study, we performed identification and preliminary characterization of the bovine PD‐1 gene in two breeds of cattle. We cloned full cDNA sequences encoding for PD‐1 from both Holstein‐Friesian and Japanese Black breeds, and found that both of the genes encoded a 282‐amino acid protein, which had a signal sequence, transmembrane domain and an immunoreceptor tyrosine‐based inhibitory motif. This bovine PD‐1 showed 72.9% and 65.6% homology to human and mouse PD‐1, respectively, both of which have been well characterized and documented. Quantitative real‐time PCR analysis showed that bovine PD‐1 is expressed predominantly in T‐cells (such as CD4⁺ and CD8⁺ cells) and among PBMCs, and is strongly upregulated on T‐cell stimulation via ConA. A limited number of cattle were tested yet, as expected, the degree of PD‐1 mRNA expression in CD4⁺ and CD8⁺ T‐cells was greater in cattle with bovine leukemia virus‐induced lymphoma than in uninfected cattle. Further studies to characterize the functions of bovine PD‐1 are therefore warranted, in order to elucidate the mechanism of the immunosuppression associated with progression of several diseases and therapy in cattle.