Increased levels of plasma galectin-9 in patients with influenza virus infection.

Galectin-9 (Gal-9) is a ß-galactoside-binding protein involved in various biologic processes, including cell aggregation, adhesion, chemoattraction, and apoptosis. Little is known, however, about the regulation mechanisms of Gal-9 production. Recent studies reported high plasma Gal-9 levels in humans infected with human immunodeficiency virus-1 and dengue virus. Viral respiratory infections such as influenza are common human illnesses. A synthetic double-stranded RNA, polyinosinic-polycytidylic acid (PolyIC), mimics the effects of viruses in various cell types and induces the expression of Gal-9 in endothelial cells. To examine the potential link between viral infection and Gal-9 expression, we measured plasma Gal-9 concentrations in patients with influenza. Subjects were 43 patients with influenza virus infection, 20 with pneumococcal pneumonia, and 20 healthy adults. Gal-9 concentrations in the plasma and in culture supernatants of human airway epithelial cells were measured using an enzyme-linked immunosorbent assay. Plasma Gal-9 concentrations were higher in patients with influenza infection than in patients with pneumococcal pneumonia and healthy subjects (p < 0.05). Patients with influenza were effectively differentiated from those with pneumococcal pneumonia or healthy subjects, based on the plasma levels of Gal-9 (p < 0.0001). Furthermore, using a human airway epithelial cell line, we showed that the presence of PolyIC but not lipopolysaccharides increased the Gal-9 concentration in the culture medium (p < 0.05), suggesting that PolyIC enhanced Gal-9 production. These findings support our proposal that Gal-9 production is induced by influenza virus infection in humans. In conclusion, plasma Gal-9 could be a new biomarker for patients with influenza infection.

Preventive effect of galectin-9 on double-stranded RNA-induced airway hyperresponsiveness in an exacerbation model of mite antigen-induced asthma in mice.

BACKGROUND: Viral respiratory infection is the most common cause of acute asthma exacerbation in patients with stable asthma. The replication of most respiratory viruses requires the generation of double-stranded RNA (dsRNA), resulting in the activation of host immune responses. Synthetic dsRNA, polyinosinic-polycytidylic acid (PolyIC), mimics the effects of viruses in various cell types. To evaluate new therapies for mite antigen-induced chronic asthma, we developed an acute exacerbation model of mouse chronic asthma using mite antigen and PolyIC. We also examined the preventive effects of recombinant galectin-9 (Gal-9) on acute asthma exacerbation in this model. METHODS: Airway hyperresponsiveness (AHR) was examined to evaluate the exacerbation of chronic asthma. To analyze airway inflammation, the numbers of inflammatory cells and concentrations of cytokines in the bronchoalveolar lavage fluid (BALF) were estimated by flow cytometry and enzyme-linked immunosorbent assay, respectively. RESULTS: AHR was accelerated by intranasal administration of PolyIC in addition to mite antigen. Levels of cytokines that contribute to AHR, including interferon-γ, tumor necrosis factor-α, and RANTES (CCR5), and of Gal-9 in the BALF were elevated in this acute asthma exacerbation mouse model. Intranasal administration of recombinant Gal-9 reduced the PolyIC-induced AHR and levels of these cytokines in the BALF. Further, Gal-9 suppressed the production of cytokines induced by PolyIC in the alveolar macrophages. CONCLUSIONS. Our findings demonstrated that exogenous Gal-9 suppressed dsRNA-induced AHR in an acute exacerbation model of chronic asthma in mice, and suggest that recombinant Gal-9 could be therapeutically effective for preventing acute asthma exacerbation.

Possible regulatory role of galectin-9 on Ascaris suum-induced eosinophilic lung inflammation in mice.

BACKGROUND: Galectin-9 (Gal-9) is a member of the galectin family of lectins that exhibit binding affinity for ß-galactosides. We found a T cell line-derived Gal-9 with novel eosinophil chemoattractant activity, but its role in eosinophilic inflammation of the lung is unknown. We evaluated the role of Gal-9 in Ascaris suum-induced eosinophilic lung inflammation in mice. METHODS: To evaluate the role of Gal-9 in Ascaris suum-induced eosinophilic lung inflammation, we developed a mouse model of eosinophilic pneumonia induced by the Ascaris suum antigen, and analyzed eosinophilic inflammation in Gal-9-deficient mice. The therapeutic effects of recombinant Gal-9 on lung inflammation were also examined in this mouse model. To evaluate lung inflammation, numbers of inflammatory cells and cytokine levels in the bronchoalveolar lavage fluid (BALF) were estimated by flow cytometry and enzyme-linked immunosorbent assay, respectively. RESULTS: The BALF of this mouse model of eosinophilic pneumonia induced by the Ascaris suum antigen contained increased numbers of inflammatory cells and elevated Gal-9 levels. Compared with wild-type mice, the BALF of Gal-9-deficient mice contained higher numbers of both eosinophils and T helper type 2 (Th2) cells. Th2 cytokines and eotaxin levels were also higher, and levels of CD4+CD25+Foxp3+ regulatory T cells were lower in Gal-9-deficient mice than in wild-type mice. Intranasal administration of recombinant Gal-9 prevented eosinophilic inflammation of the lung and upregulated the release of endogenous Gal-9. CONCLUSIONS: Our findings suggest that Gal-9 negatively regulates Th2-mediated eosinophilic inflammation of the lung and that Foxp3+ regulatory T cells might be involved in suppressing allergic inflammation.