An important interplay exists between specific viral respiratory infections and altered airway responsiveness in the development and exacerbations of asthma. However, the mechanistic basis of this interplay remains to be identified. This study addressed the hypothesis that rhinovirus (RV), the most common viral respiratory pathogen associated with acute asthma attacks, directly affects airway smooth muscle (ASM) to produce proasthmatic changes in receptor-coupled ASM responsiveness. Isolated rabbit and human ASM tissue and cultured ASM cells were inoculated with human RV (serotype 16) or adenovirus, each for 6 or 24 h. In contrast to adenovirus, which had no effect, inoculation of ASM tissue with RV induced heightened ASM tissue constrictor responsiveness to acetylcholine and attenuated the dose-dependent relaxation of ASM to beta-adrenoceptor stimulation with isoproterenol. These RV-induced changes in ASM responsiveness were largely prevented by pretreating the tissues with pertussis toxin or with a monoclonal blocking antibody to intercellular adhesion molecule-1 (ICAM-1), the principal endogenous receptor for most RVs. In extended studies, we found that the RV-induced changes in ASM responsiveness were associated with diminished cAMP accumulation in response to dose-dependent administration of isoproterenol, and this effect was accompanied by autologously upregulated expression of the Gi protein subtype, Gialpha3, in the ASM. Finally, in separate experiments, we found that the RV-induced effects on ASM responsiveness were also accompanied by autologously induced upregulated mRNA and cell surface protein expression of ICAM-1. Taken together, these findings provide new evidence that RV directly induces proasthmatic phenotypic changes in ASM responsiveness, that this effect is triggered by binding of RV to its ICAM-1 receptor in ASM, and that this binding is associated with the induced endogenously upregulated expression of ICAM-1 and enhanced expression and activation of Gi protein in the RV-infected ASM.
H Hakonarson, N Maskeri, C Carter, R L Hodinka, D Campbell, M M Grunstein
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