Maturation of circulating Ly6ChiCCR2+ monocytes by mannan-MOG induces antigen-specific tolerance and reverses autoimmune encephalomyelitis

Abstract

Autoimmune diseases affecting the CNS not only overcome immune privilege mechanisms that protect neural tissues but also peripheral immune tolerance mechanisms towards self. Together with antigen-specific T cells, myeloid cells are main effector cells in CNS autoimmune diseases such as multiple sclerosis, but the relative contributions of blood-derived monocytes and the tissue resident macrophages to pathology and repair is incompletely understood. Through the study of oxidized mannan-conjugated myelin oligodendrocyte glycoprotein 35-55 (OM-MOG), we show that peripheral maturation of Ly6ChiCCR2+ monocytes to Ly6ChiMHCII+PD-L1+ cells is sufficient to reverse spinal cord inflammation and demyelination in MOG-induced autoimmune encephalomyelitis. Soluble intradermal OM-MOG drains directly to the skin draining lymph node to be sequestered by subcapsular sinus macrophages, activates Ly6ChiCCR2+ monocytes to produce MHC class II and PD-L1, prevents immune cell trafficking to spinal cord, and reverses established lesions. We previously showed that protection by OM-peptides is antigen specific. Here, using a neutralizing anti-PD-L1 antibody in vivo and dendritic cell-specific Pdl1 knockout mice, we further demonstrate that PD-L1 in non-dendritic cells is essential for the therapeutic effects of OM-MOG. These results show that maturation of circulating Ly6ChiCCR2+ monocytes by OM-myelin peptides represents a novel mechanism of immune tolerance that reverses autoimmune encephalomyelitis.

Discrepant Phenotyping of Monocytes Based on CX3CR1 and CCR2 Using Fluorescent Reporters and Antibodies

“…Interestingly, we did not observe the differential expression of RFP in Ly6C high and Ly6C low monocytes (Figure 5a). However, using a CCR2 antibody (SA203G11, FITC, BioLegend), we were able to distinguish a Ly6C high CCR2 high and a Ly6C low CCR2 −/low population in accordance with previous reports (Figure 5a,b) [43]. Consistently, we did not observe any correlation between the CCR2 antibody and the reporter signal (Figure 5b).…”

Spontaneous human CD8 T cell and EAE-inducible human CD4/CD8 T cell lesions in the brain and spinal cord of HLA-DRB1*15-positive multiple sclerosis PBMC humanized mice

“…Unlike B6 mice, very high proportions of mouse (m) CD11b + , mCD11b + Ly6C hi and mCD11b + Ly6G + myeloid cells were already present in the blood of naive B2m-NOG and NOD-scid mice, and were not significantly increased by immunization (Supplementary Table 4). Functionality of the human immune system in B2m-NOG mice was investigated using an ex vivo proliferation assay for T cell responses in splenocytes (23), and a cell-based assay for anti-MOG antibody responses in plasma. Briefly, splenocytes recovered from non-immunized and immunized mice at sacrifice were stimulated ex vivo individually with the 4 myelin peptides used for immunization (mMOG35-55, hMOG35-55, MOG1-20, MBP83-99).…”

“…In that study, mice developed CNS inflammation differentiate into inflammatory macrophages locally in the CNS after being activated by T cells, are critical effector cells in EAE(22,36). These cells are massively recruited into the periphery from the bone marrow following immunization(23), and are likely to compete for space with engrafted human immune cells before and after EAE induction. The use of immunodeficient NOG/NSG models expressing human transgenes that would support engraftment of human monocytes, or facilitate communication of human T cells with mouse inflammatory monocytes(37,38), should allow a more comprehensive modeling of MS immunopathology in humanized mice.Another limitation for MS modeling in the B2m-NOG mice used in this study is the poor LN structure and functioning that results from depletion of the common cytokine receptor γchain gene(25).…”

The Influence of Myeloid-Derived Suppressor Cell Expansion in Neuroinflammation and Neurodegenerative Diseases

“…Contrasting results were noticed about MDSC modulation in the CNS during disease attenuation. Some authors have observed an increase in MDSC expansion after treatment [57,63,65,68], especially regarding the PMN-MDSCs [61,62,71], while others have observed a reduction in MDSCs [17,58,60,69,70]. Irrespective of MDSC variation, the amelioration of MS in CNS matches with the expansion of Tregs or IL-10 [59,66] and the reduction in Th17 and IL-17 [17,59,66,68,70,71].…”