Lung type II alveolar epithelial cells collaborate with CCR2⁺inflammatory monocytes in host defense against an acute vaccinia infection in the lungs

Abstract

3The pulmonary immune system consists of a network of tissue-resident cells as well as immune 4 cells that are recruited to the lungs during infection and/or inflammation. How the two immune 5 components cross-talk during an acute viral infection is not well understood. Intranasal infection 6 of mice with vaccinia virus causes lethal pneumonia and systemic dissemination. Here we report 7 that vaccinia host range protein C7 is a critical virulence factor. Vaccinia virus with deletion of C7 8 (VACV∆C7L) is non-pathogenic in wild-type C57BL/6J mice, but it gains virulence in mice 9 lacking STAT2, or IFNAR1, or MDA5/STING. We provide evidence that lung type II alveolar 10 epithelial cells (AECs) provide first-line of defense against VACV∆C7L infection by inducing 11 IFN-b and IFN-stimulated genes via the activation of the MDA5 and STING-mediated nucleic 12 acid-sensing pathways. This leads to recruitment of CCR2 + inflammatory monocytes into the lungs 13 to fight against viral dissemination. 14 In this study, we first demonstrated that vaccinia host range protein C7 is a virulence factor. 45 VACV∆C7L is non-pathogenic in WT C57BL/6J mice at a high dose of infection intranasally, but 46 gained virulence in STAT2, IFNAR1, or MDA5/STING-deficient mice. VACV∆C7L is non-47 pathogenic in RAG1-deficient mice, which lack T and B cells. Thus, this attenuated VACV mutant 48provides us with a model to evaluate the lung innate immune responses to acute pulmonary 49 infection with a DNA virus. We found that VACV∆C7L infection triggers the release of IFN-b, 50 CCL2, CXCL9, and CXCL10 into bronchioalveolar (BAL), whereas WT VACV infection fails to 51 do so. Infection of primary lung AECII with VACV∆C7L in vitro leads to the induction of IFNB 52 and IFN-stimulated genes (ISGs), which is dependent on the MDA5-dependent cytosolic dsRNA-53 sensing pathway as well as the STING-dependent cytosolic DNA-sensing pathway. 54 55 Given that both IFNAR1 and STAT2-deficient mice are more susceptible to VACV∆C7L 56 infection, we hypothesize that type I IFN signaling plays an important role in restricting 57 VACV∆C7L, either through stimulating IFNAR on the lung AEC and/or hematopoietic cell 58 populations. To probe the relative contributions of lung non-hematopoietic resident cells versus 59 hematopoietic cells in host defense against VACV∆C7L, we generated bone marrow chimeric 60 mice. Our results indicate that the IFNAR signaling on the non-hematopoietic cells (likely the 61 AECII) plays a critical role in host defense, and IFNAR signaling on hematopoietic cells also 62 contributes. Using IFNAR1 fl/fl -Sftpc cre-ERT2 mice, we showed that type I IFN signaling on lung 63AECIIs is important for host defense against VACV∆C7L infection. 64 65To probe whether myeloid cells play a role in host defense against VACV∆C7L infection, we 66 transiently depleted CCR2 + inflammatory monocytes in CCR2-DTR mice through administration 67 of diphtheria toxin (DT), and found that depletion of CCR2 + inflammatory monocytes renders the 68 mice susceptible to VACV∆C7...

Heat-inactivated modified vaccinia virus Ankara boosts Th1-biased cellular and humoral immune responses as a vaccine adjuvant by activating the STING-mediated cytosolic DNA-sensing pathway

“…By contrast, MVA infection induces IFN production via the cGAS/STING-mediated cytosolic DNA-sensing pathway 20 . Vaccinia virus encodes many immunomodulatory genes to evade the host immune system [21][22][23] . Inactivation of WT VACV or MVA, by heating MVA at 55°C for 1h, reduces infectivity by 1000-fold and much more potently induces type I IFN production than live viruses in conventional DCs (cDCs) or plasmacytoid DCs (pDCs) [24][25][26] .…”