Severe acute respiratory syndrome coronavirus (SARS-CoV) is a recently identified human coronavirus. The extremely high homology of the viral genomic sequences between the viruses isolated from human (huSARS-CoV) and those of palm civet origin (pcSARS-CoV) suggested possible palm civet-to-human transmission. Genetic analysis revealed that the spike (S) protein of pcSARS-CoV and huSARS-CoV was subjected to the strongest positive selection pressure during transmission, and there were six amino acid residues within the receptor-binding domain of the S protein being potentially important for SARS progression and tropism. Using the single-round infection assay, we found that a two-amino acid substitution (N479K/T487S) of a huSARS-CoV for those of pcSARS-CoV almost abolished its infection of human cells expressing the SARS-CoV receptor ACE2 but no effect upon the infection of mouse ACE2 cells. Although single substitution of these two residues had no effects on the infectivity of huSARS-CoV, these recombinant S proteins bound to human ACE2 with different levels of reduced affinity, and the two-amino acid-substituted S protein showed extremely low affinity. On the contrary, substitution of these two amino acid residues of pcSARS-CoV for those of huSRAS-CoV made pcSARS-CoV capable of infecting human ACE2-expressing cells. These results suggest that amino acid residues at position 479 and 487 of the S protein are important determinants for SARS-CoV tropism and animal-to-human transmission.

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Macrophages play a pivotal role in tumor microenvironment. Bu-Fei Decoction (BFD) is a classical formula of traditional Chinese medicine (TCM) to alleviate lung cancer related symptoms, whether it has antitumor effect or could influence cancer microenvironment deserves further study. The aim of the present study was to examine the antitumor effect of BFD on non-small cell lung cancer (NSCLC), and to investigate the underlying mechanisms through tumor associated macrophages (TAMs). M2-polarized TAMs were induced by Phorbol 12-myristate 13-acetate (PMA) and interleukin 4 (IL-4). The antitumor activity of BFD in vitro was investigated in A549 and H1975 cells using MTT assay. The in vivo anticancer effect of BFD was evaluated in athymic nude mouse xenograft model. The invasive and migration properties of NSCLC cells were measured using Transwell. The protein expression was assessed using western blotting, ELISA and immunohistochemistry. The gene expression was examined using RT-PCR. TAMs was successfully established. Conditioned medium from TAMs increased cell proliferation, migration and invasion in NSCLC cells (p<0.05). BFD showed dose-dependent inhibitory effect on cell proliferation, migration and invasion abilities induced by TAMs. TAMs and rhIL-10 promoted the mRNA and protein expression of PD-L1 in NSCLC cells (p<0.01). Anti-IL-10 antibodies inhibited the elevated PD-L1 expression induced by TAMs. In vitro, the expression of PD-L1 and IL-10 was inhibited by BFD dose-dependently. In vivo, BFD suppressed A549 and H1975 tumor growth and decreased the expression of IL-10, PD-L1 and CD206. The results showed that TAMs play an important role in tumor progression of NSCLC, which was associated with tumor proliferation, migration, invasion and immunosuppression. Moreover, the antitumor mechanism of BFD is related to interruption of the link between TAMs and cancer cells by inhibiting the expression of IL-10 and PD-L1 in vitro and in vivo. Our results demonstrated BFD's potential as a novel treatment for NSCLC.

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