Regulatory T cells hold promise as targets for therapeutic intervention in autoimmunity, but approaches capable of expanding antigen-specific regulatory T cells in vivo are currently not available. Here we show that systemic delivery of nanoparticles coated with autoimmune-disease-relevant peptides bound to major histocompatibility complex class II (pMHCII) molecules triggers the generation and expansion of antigen-specific regulatory CD4(+) T cell type 1 (TR1)-like cells in different mouse models, including mice humanized with lymphocytes from patients, leading to resolution of established autoimmune phenomena. Ten pMHCII-based nanomedicines show similar biological effects, regardless of genetic background, prevalence of the cognate T-cell population or MHC restriction. These nanomedicines promote the differentiation of disease-primed autoreactive T cells into TR1-like cells, which in turn suppress autoantigen-loaded antigen-presenting cells and drive the differentiation of cognate B cells into disease-suppressing regulatory B cells, without compromising systemic immunity. pMHCII-based nanomedicines thus represent a new class of drugs, potentially useful for treating a broad spectrum of autoimmune conditions in a disease-specific manner.

The endothelial cell monolayer of cerebral vessels and its basement membrane (BM) are ensheathed by the astrocyte endfeet, the leptomeningeal cells, and their associated parenchymal BM, all of which contribute to establishment of the blood–brain barrier (BBB). As a consequence of this unique structure, leukocyte penetration of cerebral vessels is a multistep event. In mouse experimental autoimmune encephalomyelitis (EAE), a widely used central nervous system inflammatory model, leukocytes first penetrate the endothelial cell monolayer and underlying BM using integrin β1-mediated processes, but mechanisms used to penetrate the second barrier defined by the parenchymal BM and glia limitans remain uninvestigated. We show here that macrophage-derived gelatinase (matrix metalloproteinase [MMP]-2 and MMP-9) activity is crucial for leukocyte penetration of the parenchymal BM. Dystroglycan, a transmembrane receptor that anchors astrocyte endfeet to the parenchymal BM via high affinity interactions with laminins 1 and 2, perlecan and agrin, is identified as a specific substrate of MMP-2 and MMP-9. Ablation of both MMP-2 and MMP-9 in double knockout mice confers resistance to EAE by inhibiting dystroglycan cleavage and preventing leukocyte infiltration. This is the first description of selective in situ proteolytic damage of a BBB-specific molecule at sites of leukocyte infiltration.

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Although chemokines are sufficient for chemotaxis of various cells, increasing evidence exists for their fine-tuning by selective proteolytic processing. Using a model of immune cell chemotaxis into the CNS (experimental autoimmune encephalomyelitis [EAE]) that permits precise localization of immigrating leukocytes at the blood-brain barrier, we show that, whereas chemokines are required for leukocyte migration into the CNS, additional MMP-2/9 activities specifically at the border of the CNS parenchyma strongly enhance this transmigration process. Cytokines derived from infiltrating leukocytes regulate MMP-2/9 activity at the parenchymal border, which in turn promotes astrocyte secretion of chemokines and differentially modulates the activity of different chemokines at the CNS border, thereby promoting leukocyte migration out of the cuff. Hence, cytokines, chemokines, and cytokine-induced MMP-2/9 activity specifically at the inflammatory border collectively act to accelerate leukocyte chemotaxis across the parenchymal border.

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Extracellular matrix metalloproteinase inducer (EMMPRIN, CD147) is a member of the Ig superfamily, with various physiological roles including the induction of matrix metalloproteinases (MMPs), leukocyte activation, and tumor progression. In this study, we illustrate a novel involvement of EMMPRIN in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). We found EMMPRIN levels to be upregulated on peripheral leukocytes before onset of EAE clinical signs and on infiltrating leukocytes and resident cells within the CNS in symptomatic mice. In EAE brain sections, EMMPRIN expression was localized with MMP-9 protein and activity. The increased EMMPRIN level was also characteristic of brain samples from MS subjects, particularly in plaque-containing areas. To evaluate the implications of elevated EMMPRIN levels, we treated EAE mice with an EMMPRIN function-blocking antibody and found reduced EAE clinical severity accompanied by decreased CNS parenchymal infiltration of leukocytes. Amelioration of EAE clinical signs by the anti-EMMPRIN antibody was critically dependent on its administration around the period of onset of clinical signs, which is typically associated with significant influx of leukocytes into the CNS. Moreover, the reduction in disease severity in anti-EMMPRINtreated mice was associated with diminished MMP proteolytic activity at the glia limitans, the final barrier before parenchymal infiltration of leukocytes. Together, our results are the first to emphasize a role for EMMPRIN in MS and EAE, whereby EMMPRIN regulates leukocyte trafficking through increasing MMP activity. These results identify EMMPRIN as a novel therapeutic target in MS.

Inflammatory perivascular cuffs are comprised of leucocytes that accumulate in the perivascular space around post-capillary venules before their infiltration into the parenchyma of the central nervous system. Inflammatory perivascular cuffs are commonly found in the central nervous system of patients with multiple sclerosis and in the animal model experimental autoimmune encephalomyelitis. Leucocytes that accumulate in the perivascular space secrete matrix metalloproteinases that aid their transmigration into the neural parenchyma. We described previously that the upstream inducer of matrix metalloproteinase expression, extracellular matrix metalloproteinase inducer (CD147), was elevated in experimental autoimmune encephalomyelitis, and that its inhibition reduced leucocyte entry into the central nervous system. Here we investigated whether the expression of extracellular matrix metalloproteinase inducer varies with the temporal evolution of lesions in murine experimental autoimmune encephalomyelitis, whether it was uniformly upregulated across multiple sclerosis specimens, and whether it was a feature of inflammatory perivascular cuffs in multiple sclerosis lesions. In experimental autoimmune encephalomyelitis, elevation of extracellular matrix metalloproteinase inducer was correlated with the appearance and persistence of clinical signs of disease. In both murine and human samples, extracellular matrix metalloproteinase inducer was detected on endothelium in healthy and disease states but was dramatically increased in and around inflammatory perivascular cuffs on leucocytes, associated with matrix metalloproteinase expression, and on resident cells including microglia. Leucocyte populations that express extracellular matrix metalloproteinase inducer in multiple sclerosis lesions included CD4 + and CD8 + T lymphocytes, B lymphocytes and monocyte/macrophages. The extra-endothelial expression of extracellular matrix metalloproteinase inducer was a marker of the activity of lesions in multiple sclerosis, being present on leucocyte-containing perivascular cuffs but not in inactive lesions. By using a function-blocking antibody, we implicate extracellular matrix metalloproteinase inducer in the adhesion of leucocytes to endothelial cells and determined that its activity was more crucial on leucocytes than on endothelium in leucocyte-endothelial cell engagement in vitro. Extracellular matrix metalloproteinase inducer activity regulated the level of alpha 4 integrin on leucocytes through a mechanism associated with nuclear factor kB signalling. Blocking extracellular matrix metalloproteinase inducer attenuated the transmigration of monocytes and B lymphocytes across a model of the blood-brain barrier in culture. In summary, we describe the prominence of extracellular matrix metalloproteinase inducer in central nervous system inflammatory perivascular cuffs, emphasize its dual role in matrix metalloproteinase induction and leucocyte adhesion, and highlight the elevation of extracellular matrix metalloproteinase inducer...