| Rhinovirus (RV) infections trigger the majority of asthma and COPD exacerbations. However, the underlying mechanisms have not been well-studied. Clinical studies suggest RV may potentiate pre-existing pro-inflammatory pathways, enhancing chemokine production and airway inflammation. However, RV replication is optimal between 33°--35°C, and therefore the quantity of RV replication in the lower airways may be limited. We hypothesized that pathways activated prior to RV replication may be sufficient for a subset of signaling responses, explaining how RV could induce chemokine expression and inflammation without substantial replication. We also hypothesized that RV infection activates pathways involved in the asthmatic response, leading to cooperative effects. Infection of 16HBE14o- cells with RV39 induced phosphorylation of PI 3-kinase/Akt, JNK, ERK and Src within minutes of infection, and all were required for RV-induced IL-8 production. PI 3-kinase/Akt signaling was also required for RV39 internalization and sufficient for NF-kappaB activation. Further, co-stimulation of cells with RV39 and TNF-alpha, a cytokine found in the airways of patients with asthma, induced cooperative increases in IL-8 and ENA-78 expression as well as AP-1 and NF-kappaB transactivation. Finally, we developed a C57BL/6 mouse model of RV infection using the minor group virus RV1B. Prior development was hindered by species variation in RV major group receptor, ICAM-1. However, using RV1B, which binds to LDL-receptor, we detected RV RNA in the lungs of RV1B-infected mice, but not in mice infected with replication-deficient UV-irradiated RV1B (UV RV1B) or RV39, a major group virus. RV1B infection induced neutrophilic airway inflammation, hyperresponsiveness and increased lung expression of KC, MIP-1alpha, MIP-2, RANTES and JE, as well as IFN-beta and gamma. RV39 did not increase chemokine or cytokine production, demonstrating that the observed inflammation was a specific response to RV1B infection. On the other hand, UV-irradiated RV1B caused intermediate increases in neutrophilia and MIP-2 expression. RV1B and UV RV1B infections increased phosphorylation of Akt, and RV1B and phosphorylated Akt were co-localized in the airway epithelium. Pre-treatment with LY294002 prior to infection attenuated RV-induced neutrophil infiltration and chemokine production. Thus, PI 3-kinase/Akt signaling is required for RV-induced responses in vivo as it is in vivo. |
