Innate IFN-γ ameliorates experimental autoimmune encephalomyelitis and promotes myeloid expansion and PDL-1 expression

The innate immune system plays a central role in the immune-mediated pathology of multiple sclerosis, and is a therapeutic target for progressive disease. Recently, it has been demonstrated that MIS416, a novel immunomodulatory microparticle that activates NOD-2 and TLR-9-signaling, has disease-modifying activity in multiple sclerosis models. This activity is dependent on innate IFN-γ; however, the precise immune regulatory mechanisms amplified by MIS416 have not previously been determined. Using the experimental autoimmune encephalomyelitis model, MIS416 treatment was associated with IFN-γ–dependant expansion of Treg number and increased suppressive function; however, these cells did not account for disease reduction. Additionally, MIS416 treatment stimulated increased nitric oxide production that was IFN-γ–dependant but dispensable for protection. Finally, MIS416-mediated protection was shown to correlate with IFN-γ–dependant expansion of PDL-1-expressing peripheral myeloid cells, a subset of which was found to be selectively recruited to the brain. This central nervous system trafficking was independent of neuro-inflammatory signals as it occurred in MIS416-treated healthy mice. Together, these findings provide insight into regulatory myeloid cell activities amplified by MIS416-mediated NOD-2 and TLR-9 signalling and highlight the potential importance of these cells in accessing the brain where they may act locally and contribute to the control of neuroinflammation.