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

Abstract

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.

Innate signaling within the central nervous system recruits protective neutrophils

“…These were upregulated in CNS by intrathecal MIS416. Intrathecal and intravenous MIS416 both induced PDL-1+ myeloid populations, shown to be IFNγ-dependent in the case of peripheral suppression, where PDL-1+ monocytes also infiltrated the CNS [34]. PD1 inhibitory signaling may be considered as a possible mechanism for intra-CNS EAE suppression, although in the present study, PDL-1 was expressed by both the neutrophils and monocytes that were recruited by MIS416, so did not correlate with suppressive function.…”

“…PD1 inhibitory signaling may be considered as a possible mechanism for intra-CNS EAE suppression, although in the present study, PDL-1 was expressed by both the neutrophils and monocytes that were recruited by MIS416, so did not correlate with suppressive function. Suppression of EAE by iv-administered MIS416 was dependent on innate IFNγ [34], whereas we show dependence on Type I IFN. In another study we showed that IFNγ could substitute for Type I IFN signaling [2], and it cannot be excluded that an analogous functional overlap contributed in the myeloid suppression of CNS inflammation that we describe here.…”

“…Previous description of EAE-protection induced by intravenous MIS416 showed mobilization of neutrophils and monocytes, increased number of splenic neutrophils, and IFNγ-dependent suppression of encephalitogenic T cell responses, but we show here that only MIS416phagocytosing monocytes trafficked to the CNS from the periphery. Our transfer experiments would suggest that these were not suppressive, and that peripheral anti-inflammatory programs were more important in those studies [34]. We have taken advantage of MIS416 as a tool to investigate CNS endogenous signals and phagocytosis in EAE, to probe the immunological pathways that favor regulatory myeloid activity with focus on innate interferon signaling.…”

“…It was previously shown that iv administration of MIS416 increased numbers of T cells, macrophages and monocytic myeloid cells, but not neutrophils, in the CNS of healthy mice, although iv MIS416 did induce an increase in splenic neutrophils [34]. We have repeated this analysis using fluorescent-tagged MIS416-AF488 and show a great predominance of monocytic myeloid CD11b + F4/80 + Gr1 − CD11c + cells among the CNSinfiltrating MIS416-phagocytosing CD45 high cells 24 h after intravenous injection (Fig.…”

“…Here we have used a bispecific innate-signaling immunomodulatory microparticle, in order to probe the ability of phagocytic myeloid cells within the CNS to recruit a protective myeloid response. Microparticle Immune Stimulator-416 (MIS416), originally developed as a vaccine adjuvant [5], is a modified bacterial cell body that is a specific agonist for TLR9 and NOD2 [16,34]. MIS416 has been shown to suppress EAE when given peripherally to mice [34], and it has also been shown to enhance protection in mesenchymal stem cell therapy and to target myeloid suppressor cells in tumors [10,14].…”