Abstract

Proteinase-activated receptor 2 (PAR₂) is widely expressed in the respiratory tract and is an integral component of the host antimicrobial defense system. The principal aim of this study was to investigate the influence of a PAR₂-activating peptide, SLIGRL, on influenza A virus (IAV)-induced pathogenesis in mice. Intranasal inoculation of BALB/c mice with influenza A/PR/8/34 virus caused time-dependent increases in the number of pulmonary leukocytes (recovered from bronchoalveolar lavage fluid), marked airway histopathology characterized by extensive epithelial cell damage, airway hyper-responsiveness to the bronchoconstrictor methacholine, and elevated levels of inflammatory chemokines (keratinocyte-derived chemokine and macrophage inflammatory protein 2) and cytokines (interferon-γ). It is noteworthy that these IAV-induced effects were dose-dependently attenuated in mice treated with a PAR₂-activating peptide, SLIGRL, at the time of IAV inoculation. However, SLIGRL also inhibited IAV-induced increases in pulmonary leukocytes in PAR₂-deficient mice, indicating these antiviral actions were not mediated by PAR₂. The potency order obtained for a series of structural analogs of SLIGRL for anti-IAV activity (IGRL > SLIGRL > LSIGRL >2-furoyl-LIGRL) was also inconsistent with a PAR₂-mediated effect. In further mechanistic studies, SLIGRL inhibited IAV-induced propagation in ex vivo perfused segments of trachea from wild-type or PAR₂(−/−) mice, but did not inhibit viral attachment or replication in Madin-Darby canine kidney cells and chorioallantoic membrane cells, which are established hosts for IAV. In summary, SLIGRL protected mice from IAV infection independently of PAR₂ and independently of direct inhibition of IAV attachment or replication, potentially through the activation of endogenous antiviral pathways within the mouse respiratory tract.