BackgroundPD-L1 expression on neutrophils contributes to the impaired immune response in infectious disease, but the detailed role of PD-L1 expression on neutrophils in HCC remains unclear.MethodsWe investigated the phenotype and morphology of neutrophils infiltrated in tumour tissues from both patients with HCC and hepatoma-bearing mice.ResultsWe found that neutrophils dominantly infiltrated in the peritumoural region. The neutrophil-to-T cell ratio (NLR) was higher in peritumoural tissue than that in the intratumoural tissue and was negatively correlated with the overall survival of patients with HCC. Infiltrating neutrophils displayed a phenotype of higher frequency of programmed cell death ligand 1 (PD-L1) positive neutrophils. The ratio of PD-L1+ neutrophils-to-PD-1+ T cells was higher in peritumoural tissue and better predicted the disease-free survival of patients with HCC. We further confirmed a higher frequency of PD-L1+ neutrophils and PD-1+ T cells in hepatoma-bearing mice. Functionally, the PD-L1+ neutrophils from patients with HCC effectively suppressed the proliferation and activation of T cells, which could be partially reversed by the blockade of PD-L1.ConclusionsOur results indicate that the tumour microenvironment induces impaired antitumour immunity via the modulation of PD-L1 expression on tumour infiltrating neutrophils.Electronic supplementary materialThe online version of this article (doi:10.1186/s13046-015-0256-0) contains supplementary material, which is available to authorized users.

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To investigate the apoptosis effect of SARS coronavirus nucleocapsid protein on cultured cell lines and to explore the possible pathway of apoptosis. pCDNA3.1(-)/his-myc vector containing the SARS coronavirus nucleocapsid gene (N), matric gene (M), spike gene (S) were transfected into COS-1, Huh-7 and HepG2 cells. Apoptosis induced by SARS coronavirus N protein under starvation of serum of COS-1 cells was monitored by Annexin V and electron microscopy assays. Intracellular reactive oxygen species (ROS) and mitochondrial membrane potential (DeltaPsim) were determined by flow cytometric assay. Cytochrome C, cleaved caspase (cysteine aspartic acid protease)-3, 9, and poly (ADP-ribose) polymerase (PARP) were detected by Western blot. After removal of serum in COS-1 cells, we observed the loss of DeltaPsim, the increase of ROS and cytochrome C release into cytosol and subsequent activation of caspase-3 and PARP cleavage. The pan-caspase inhibitor z-VAD-fmk can block the activation of caspase 3, 9 and PARP cleavage. In conclusion, SARS coronavirus N protein can induce apoptosis of COS-1 cells by activating mitochondrial pathway. SARS coronavirus M, S protein can not induce apoptosis in COS-1, HepG2 and Huh-7 and SARS coronavirus N protein can not induce apoptosis in HepG2 and Huh-7 by methods used in this study.

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