Notch Signaling Negatively Regulates Pathogenic IL-17 Production from Th17 cells during γ-Herpesvirus Induced Pneumonitis and Pulmonary Fibrosis Following Bone Marrow Transplantation

Abstract

Abstract The Notch signaling pathway is an important mediator of T-cell cytokine responses in a variety of immunological maladies such as GVHD, rheumatoid arthritis, and systemic lupus erythematosus. Using a genetically altered mouse model wherein CD4+ and CD8+ T-cells were ablated for all Notch signaling through expression of a dominant negative version of the Notch transcriptional regulator Mastermind Like Ligand (DNMAML) we have identified Notch as a regulator of cytokines during Murine Gamma Herpesvirus 68 (MHV-68) infection following bone marrow transplantation (BMT). Wild type syngeneic BMT mice infected with MHV-68 develop severe pneumonitis and pulmonary fibrosis by 21 dpi driven in part by a switch from TH1 to TH17 mediated immunity. Expression of the Notch ligands DLL1, DLL4, Jagged1, and Jagged2 were decreased in the lungs following BMT and CD4+ T-cells isolated from the lungs and spleens of infected WT BMT mice displayed defects in Notch signaling resulting in decreased expression of Notch target genes. T-cell Notch deficient DNMAML BMT mice developed increased fibrosis 21 dpi in comparison to wild type BMT mice, and displayed elevated levels of IL-17 and IL-6 in the lungs as well as an expansion of TH17 cells and a decrease in TH1 cells. Further, both in vitro culture of BMT lung leukocytes with recombinant DLL4 and adoptive transfer of WT CD11C+ APCs after BMT restored T-cell Notch signaling, decreasing production of IL-17 and rescuing fibrotic pathology. Thus, alterations in T-cell Notch signaling during γ-herpesvirus challenge following BMT correlated with increased expression of IL-17 from TH17 cells shifting the immunologic balance from a protective TH1 response towards a pathogenic TH17 response.