Methods: Female BALB/c mice, aged 8 weeks, were divided into 3 groups. The first group was intranasally (i.n.) infected with 50 µl/mouse RSV strain A2 (5×105 TCID50/mouse). The second group received UV-inactivated RSV. The third group was treated with PBS only. On day 6 after infection, airway hyperresponsiveness (AHR) to methacholine was measured by whole-body plethysmography. The left lung was removed for histological analysis. One lobe of the right lung was taken for viral RNA (vRNA), mRNA-IL-33 evaluation by qPCR and the other lobes was used for preparing of cell suspension by collagenase digestion. Cell suspension was stained with fluorophore labeled antibodies to determine IL-33 intracellular expression in CD45+3+ T cells, CD45+19+ B cells, CD45+CD3-CD19-Ly-6G- cells, CD45-324+ epithelial cells by flow cytometry.
Results: vRNA copy number in lung tissue of RSV-infected animals was 4.3-fold higher than in mice treated with inactivated virus. AHR to inhaled methacholine in RSV-infected animals was increased compared to mice treated with inactivated virus or PBS. Histological analysis revealed the presence of inflammation characterized by infiltration of lymphocytes into the lung tissue of RSV-infected animals. These data indicate RSV infection in the mouse lungs. mRNA-IL-33 expression in lungs was 2.5-fold up-regulated upon RSV infection. Flow cytometry analysis revealed 1.7- and 1.5-fold increase in the percent of IL-33+ T-cells and CD45+CD3-CD19-Ly-6G-IL-33+ cells, respectively. We found that RSV increased (1.5 fold) the mean fluorescence intensity of IL-33 on B-cell population. In addition, IL-33 intracellular protein expression was slightly increased in epithelial cells (1.2-fold).
Conclusion: Our results provide evidence for up-regulation of IL-33 in T-, B- and CD45+CD3-CD19-Ly-6G-cells in RSV-infected murine lungs that may indicate an important role of IL-33 in virus-induced lung infections. The study was supported by RSF Grant 14-15-00894.