Figure 2
Reduced susceptibility to HRV16 infection in bronchial epithelium with IL-13-induced mucous cell metaplasia (MCM). (a) Air–liquid interface (ALI) differentiated bronchial epithelium was cultured with IL-13, IL-17A, or TGF-β (or w/o cytokines) and then infected 48 h with HRV16. (b) HRV16 titer in apical secretions in the indicated conditions, the inoculum (inoc.), and after wash (residual). (c) Expression of HRV16-RNA in cell lysates. (d) Relative expression of antiviral genes, including toll-like receptors (TLRs), dsRNA sensors, interferons (IFNs), and interferon-stimulated genes (ISGs) in the HRV16-infected mucociliary epithelium (control conditions) compared to mock (n = 19, 2-sided paired t-test P < 0.05, FDRt q = 0.05). (e) Fold differences (HRV16 vs. mock) in the expression of antiviral genes in bronchial epithelium exposed to IL-13 or in control conditions. (f) Fold change in the expression of IFNL1 mRNA, and (g) in the level of IL-29 in cell culture supernatant upon HRV16 infection in different conditions. Statistics (‘b’, ‘c’, ‘f’ and ‘g’): Bars represent means and SD (n = 40). RM 1-way ANOVA (Tukey): *P < 0.05, **P < 0.01. (h) Correlation heat map (Pearson’s coefficients [RP]; control conditions) showing the association between baseline mRNA expression of viral response (left) or structural (right) genes, and subsequent response to HRV16 (e.g., HRV-RNA and type III IFNs). n = 19, *P < 0.01. (i) A model of putative mechanism of HRV infection in remodeled bronchial epithelium. (1) The exposure of bronchial epithelium to IL-13 induces MCM, while stimulation with TGF-β leads to epithelial-mesenchymal transition (EMT). (2) MCM renders the epithelium less sensitive to infection, as HRV targets primarily sparsely distributed ciliated cells and does not efficiently replicate in mucous cells due to their ‘antiviral state’, while epithelium with EMT is more permissive to HRV infection. (3) The magnitude of innate inflammatory response is determined by HRV replication rate and autocrine action of type I and III IFNs.
