Inducible epithelial resistance improves survival of Sendai virus pneumonia in mice by both inactivating virus and preventing CD8⁺T cell-mediated immunopathology

Abstract

17Viral pneumonias remain a global health threat necessitating novel strategies to prevent 18 and treat these lower respiratory tract infections. We have reported that mice treated 19 with a combination of inhaled Toll-like receptor (TLR) 2/6 and TLR 9 agonists (Pam2-20 2 ODN) are broadly protected against respiratory pathogens. Although a single inhalation 21 of Pam-ODN prevents acute morbidity and chronic complications associated with viral 22 pneumonias, the mechanisms underlying this protection remain incompletely elucidated. 23Here, we show in a lethal paramyxovirus model that Pam2-ODN-enhanced survival is 24 associated with robust virus inactivation that occurs prior to internalization by lung 25 epithelial cells. However, it was also noted that viral mortality in sham-treated mice 26 temporally corresponded with CD8 + T cell-enriched lung inflammation that peaks after 27 the viral burden wanes. Pam2-ODN treatment also blocked this injurious inflammation, 28 but the attenuation of lymphocytic inflammation and the reduction in virus burden were 29 both lost when inducible reactive oxygen species generation was inhibited. Depleting 30 CD8 + T cells before or after viral challenge underscored the balanced roles of CD8 + T 31 cells in antiviral immunity and fatal immunopathology, but did not obviate the Pam2-32 ODN antiviral protection. These findings identify multifunctional inducible antiviral 33 mechanisms and may reveal means to protect susceptible individuals against 34 respiratory infections. 35 36 42 3 development of novel therapeutic anti-viral strategies is required to effectively prevent 43 and treat respiratory infections and their associated chronic complications 8-10 . 44 While lung epithelial cells are the principal targets of most respiratory viruses, there is 45 expanding evidence that lung epithelia are capable of generating anti-microbial 46 responses 7,11 . We hypothesized that lung epithelial cells can be harnessed to control 47 virus replication, thereby enhancing acute survival and reducing chronic complications 48 of virus infections 12-15 . Our group has previously described the phenomenon of inducible 49 epithelial resistance wherein the lungs' mucosal defenses can be broadly stimulated to 50 protect against a wide range of respiratory pathogens, including viruses 12-17 . This 51 protection is induced by a single inhalation of a combination treatment consisting of Toll 52 like receptor (TLR) 2/6 and 9 agonists (Pam2-ODN) before or after viral challenge. 53 While no individual leukocyte populations have been identified as critical for Pam2-54 ODN-induced resistance, lung epithelial cells are essential to the inducible anti-viral 55 response 12 . Further, we have shown that Pam2-ODN mediated protection is dependent 56 upon epithelial generation of reactive oxygen species (ROS) but, interestingly, does not 57 require Type I interferons 16,17 . More recently, we have shown prevention of chronic 58 virus-induced asthma in mice treated with Pam2-ODN but we have not clarified the anti-59 vi...