The anti-inflammatory response in mice with coronavirus-induced encephalomyelitis

Infections in the central nervous system pose a considerable challenge to the host. On one hand, a quick and rapid immune response is important to control the infection, while on the other hand, too robust a response can damage the CNS, which has poor regenerative properties. Therefore, nowhere else in the body is such a balance between pro- and anti-inflammatory mediators as important. Mice infected with the coronavirus, mouse hepatitis virus strain J2.2-V-1, are a useful model for understanding the two sides of the immune system. In this neurotropic viral infection, demyelination occurs secondary to the immune response's control of the viral infection. Thus, J2.2-V-1 infection also functions as an infectious animal model for multiple sclerosis (MS). Many arms of the pro-inflammatory immune system have been studied during J2.2-V-1 infection but the anti-inflammatory immune response has not been thoroughly investigated prior to this study. The data demonstrated here represent an in-depth look into the role of regulatory T cells and IL-10 during J2.2-V-1 infection. Specifically, by adoptive transfer of Tregs, I show that there is a relative paucity of Tregs during J2.2-V-1 infection in C57BL/6 mice and their addition decreases clinical scores, demyelination and the T cell response during infection without affecting viral clearance. A RAG1-/- adoptive transfer model demonstrates clinical results consistent with results obtained in B6 mice, while further demonstrating that Tregs function in the draining cervical lymph node by dampening dendritic cell activation and pro-inflammatory chemokine and cytokine release. There is also a relative decrease in T cell proliferation. Thus, Tregs are protective in J2.2-V-1-induced encephalomyelitis and their enhancement is a potential therapy for MS. Additionally, IL-10 is an important anti-inflammatory component of the immune response, as its absence causes increased immunopathology with increased demyelination in J2.2-V-1-infected B6 mice. Through the development of a recombinant J2.2-V-1 virus that produces IL-10, I also demonstrate that increasing the level of IL-10 at the site of infection is protective early in the immune response. Antigen-specific IFN-γ+ CD4 and CD8 T cells produce IL-10 at the height of the inflammation. CD8 T cells require a high level of antigen stimulation and the most recently activated CD69+CD8 T cells express high levels of IL-10. Additionally, this IL-10 expression is transient in both CD4 and CD8 T cells, presumably only by the recently stimulated cells. Through microarray analysis, protein expression and cytolytic assay, I show that IL-10+CD8 T cells are more activated than IL-10-CD8 T cells. Nonetheless, the IL-10 produced is anti-inflammatory and its production in CD8 T cells is protective in J2.2-V-1-infected mice. Thus, the most activated and cytotoxic CD8 T cells self-regulate the immune response through the production of IL-10. Overall, these studies show that the anti-inflammatory component of the immune system is vital to protecting the host from the immunopathology that occurs during J2.2-V-1 virus clearance. Specifically, the addition of Tregs and IL-10 helps ameliorate clinical disease and demyelination. These studies suggest that increasing Tregs and/or increasing the cytokine IL-10 in patients with MS may have therapeutic potential.