Role of the Th1 and Th17 Pathway in Subacute Sclerosing Panencephalitis

Subacute sclerosing panencephalitis (SSPE) is a progressive and fatal disease caused by reactivation of a mutated measles virus in brain tissue. The process of reactivation is yet to be elucidated. In this study, the possible roles of the Th1 (interleukin [IL]-12, interferon [IFN]-γ) and the Th17 axis (IL-23, IL-17, IL-22), particularly of IL-17, in the pathogenesis of SSPE were investigated. Briefly, mononuclear cells from SSPE patients were stimulated using measles virus peptide, and the release of IL-12, IL-23, IL-22, IFN-γ, and IL-17 cytokines was measured using enzyme-linked immunosorbent assay and/or enzyme-linked immunosorbent spot assay (ELISpot). We found that in comparison to the mononuclear cells obtained from healthy donors, cells from SSPE patients exhibited increased levels of IL-12, IL-23, IL-17, IL-22, and IFN-γ cytokines in response to measles virus stimulation. However, the same result was not obtained with cytomegalovirus and phytohemagglutinin. Using flow cytometry, mononuclear cells obtained from SSPE patients and healthy controls were also analyzed for the presence of intracellular IL-17 in response to measles virus stimulation. On stimulation, the number of IL-17-positive cells were found to be higher among mononuclear cells obtained from the patients. In addition, the numbers of IL-17- and IFN-γ-positive cells were significantly increased in SSPE patients. In conclusion, this study demonstrates that both the IL-12/IFN-γ and the IL-23/IL-17/IL-22 pathways are functionally abnormal in SSPE pathogenesis. Targeting these pathways and their specific pro-inflammatory mediator production may provide a new strategy to suppress SSPE development.