Human influenza virus hemagglutinin prefers to use sialic acid (SA) receptors via α-2,6 linkages. The β-galactoside α-2,6-sialyltransferase I (ST6Gal I) protein is encoded by the ST6GAL1 gene and is responsible for the addition of α-2,6 linked SA to the Galβ1-4GlcNAc disaccharide of glycans and glycoproteins found on the cellular surface. Therefore, ST6GAL1 could be a potential target for anti-influenza therapeutics. We used specific small interfering RNAs (siRNAs) to block expression of ST6GAL1 and limit distribution of SA receptors on the surface of airway epithelial cells. The siRNA duplexes we used inhibited ST6GAL1 mRNA expression and subsequent expression of the encoding protein. As a result, synthesis of α-2,6 SA galactose was inhibited. Adsorption of influenza virus particles to the surface of cells transfected with appropriate specific siRNAs was significantly reduced. Intracellular viral genome copy number and virus titer within the supernatant of cells transfected with siRNAs was significantly reduced in a dose-dependent manner compared with those for untransfected cells and cells transfected with non-specific siRNAs. We used siRNAs targeting ST6GAL1 to inhibit the expression of certain cell surface receptors, thereby preventing virus adsorption. This resulted in the inhibition of human influenza virus infection. Our findings are a significant development in the identification of potential new anti-influenza drug targets.

Influenza B virus is a main causative pathogen of annual influenza epidemics, however, research on influenza B virus in general lags behind that on influenza A viruses, one of the important reasons is studies on influenza B viruses in animal models are limited. Here we investigated the tree shrew as a potential model for influenza B virus studies. Tree shrews and ferrets were inoculated with either a Yamagata or Victoria lineage influenza B virus. Symptoms including nasal discharge and weight loss were observed. Nasal wash and respiratory tissues were collected at 2, 4 and 6 days post inoculation (DPI). Viral titers were measured in nasal washes and tissues were used for pathological examination and extraction of mRNA for measurement of cytokine expression. Clinical signs and pathological changes were also evident in the respiratory tracts of tree shrews and ferrets. Although nasal symptoms including sneezing and rhinorrhea were evident in ferrets infected with influenza B virus, tree shrews showed no significant respiratory symptoms, only milder nasal secretions appeared. Weight loss was observed in tree shrews but not ferrets. V0215 and Y12 replicated in all three animal (ferrets, tree shrews and mice) models with peak titers evident on 2DPI. There were no significant differences in peak viral titers in ferrets and tree shrews inoculated with Y12 at 2 and 4DPI, but viral titers were detected at 6DPI in tree shrews. Tree shrews infected with influenza B virus showed similar seroconversion and respiratory tract pathology to ferrets. Elevated levels of cytokines were detected in the tissues isolated from the respiratory tract after infection with either V0215 or Y12 compared to the levels in the uninfected control in both animals. Overall, the tree shrew was sensitive to infection and disease by influenza B virus. The tree shrew to be a promising model for influenza B virus research.

Yu-Ping-Feng-San (YPFS) has been found to significantly reduce exacerbation rate and the risk of a second exacerbation in patients with chronic obstructive pulmonary disease (COPD). However, the effect of YPFS on emphysema development and its exacerbation caused by influenza virus is still unclear. This study aims to investigate the protective effect of YPFS on the impaired lung function and increased inflammation that occurs during the development and exacerbation of emphysema. This study developed an emphysema mice model using porcine pancreatic elastase (PPE) and treated it with YPFS [1 950, 975, and 487.5 mg/(kg·d)] once daily. On day 7 post-PPE challenge, peripheral leucocytes and inflammatory cells in lungs were analyzed, respectively. Pulmonary inflammatory mediators were determined. On day 28, invasive lung function and inflammatory mediators were measured. In addition, histopathological changes at both time points were assessed. We also developed an exacerbation of emphysema mouse model by intratracheally infected mice with influenza H1N1 virus on day 28. After infection, YPFS administration was discontinued, and the protective effect was determined by lung function, viral titer and cytokine levels in the lungs, and lung histopathological changes on day 5 post-infection. The results demonstrated that 32 days of YPFS administration significantly improved lung function and reduced severity of emphysema in PPE-treated mice. It significantly reduced monocytes and neutrophils, while increased lymphocytes in peripheral blood. Additionally, YPFS inhibited the accumulation of alveolar macrophages and the expression of cytokines in mice treated with PPE. MMP-9, fibronectin, and VEGF, which are inflammatory mediators associated with airway remodeling, were also inhibited by YPFS. The results also demonstrated that YPFS prophylaxis prior to viral infection benefited mice treated with PPE and H1N1 as evidenced by decreased lung cytokine levels, lowered lung index, and improved lung histopathology. YPFS prevents the development of emphysema and its exacerbation induced by influenza virus in mice. Our finding provides scientific evidence for the prophylaxis application of YPFS in mitigating acute exacerbation of chronic obstructive pulmonary disease (AECOPD).