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The trafficking of autoreactive leukocytes across the blood-brain barrier (BBB) endothelium is a hallmark of multiple sclerosis (MS) pathogenesis. Although the BBB endothelium represents one of the main central nervous system (CNS) borders to interact with the infiltrating leukocytes, its exact contribution to neuroinflammation remains understudied. Here, we show that Mcam identifies inflammatory brain endothelial cells (ECs) with pro-migratory transcriptomic signature during experimental autoimmune encephalomyelitis (EAE). In addition, MCAM was preferentially upregulated on BBB ECs in MS lesions in situ and at EAE disease onset by molecular magnetic resonance imaging. In vitro and in vivo, we demonstrate that MCAM on BBB ECs contributes to EAE development by promoting the cellular trafficking of TH1 and TH17 lymphocytes across the BBB. Lastly, we showcase ST14 as an immune ligand to brain endothelial MCAM, enriched on CD4+ T lymphocytes that cross the BBB in vitro, in vivo and in MS lesions as detected by flow cytometry on rapid autopsy derived brain tissue from MS patients. Collectively, our findings reveal that MCAM is at the center of a pathological pathway used by brain ECs to recruit pathogenic CD4+ T lymphocyte from circulation early during neuroinflammation. The therapeutic targeting of this mechanism is a promising avenue to treat MS. [ABSTRACT FROM AUTHOR]

Systemic lupus erythematosus (SLE) is characterized by the development of autoantibodies against diverse self‐antigens with damage to multiple organs. Immunization with the SLE autoantigen β2‐glycoprotein I (β2GPI) and lipopolysaccharide (LPS), a known trigger of necroptosis, induces a murine model of SLE. We hypothesized that necroptotic cells, like apoptotic cells, provide a "scaffold" of cellular self‐antigens, but, unlike apoptotic cells, necroptotic cells do so in a proinflammatory and immunogenic context. We demonstrate that β2GPI indeed binds to necroptotic cells and serves as a target for anti‐β2GPI autoantibodies. We further demonstrate that necroptotic, but not apoptotic, cells promote antigenic presentation of β2GPI to CD4 T cells by dendritic cells. Finally, we show that β2GPI/LPS‐immunized mice deficient in RIPK3 (receptor‐interacting serine/threonine‐protein kinase 3) or MLKL (mixed lineage kinase domain like), and consequently unable to undergo necroptosis, have reduced SLE autoantibody production and pathology. RIPK3−/− mice had low levels of SLE autoantibodies and no renal pathology, while MLKL−/− mice produced low levels of SLE autoantibodies initially, but later developed levels comparable with wild type (WT) mice and pathology intermediate to that of WT and RIPK3−/− mice. Serum cytokine levels induced by LPS tended to be lower in RIPK3−/− and MLKL−/− mice than in WT mice, suggesting that impaired proinflammatory cytokine production may impact the initiation of autoantibody production in both strains. Our data suggest that self‐antigen (i.e. β2GPI) presented in the context of necroptosis and proinflammatory signals may be sufficient to overcome immune tolerance and induce SLE. [ABSTRACT FROM AUTHOR]

In multiple sclerosis, encephalitogenic CD4+ lymphocytes require adhesion molecules to accumulate into central nervous system inflammatory lesions. Using proteomic techniques, we identified expression of melanoma cell adhesion molecule (MCAM) on a subset of human effector memory CD4+ lymphocytes and on human blood–brain barrier endothelium. Herein, we demonstrate that MCAM is a stable surface marker that refines the identification of interleukin 17+, interleukin 22+, RAR-related orphan receptor γ and interleukin 23 receptor+ cells within the CD161+CCR6+ subset of memory CD4+ lymphocytes. We also show that MCAM+ lymphocytes express significantly more granulocyte/macrophage colony stimulating factor and granzyme B than MCAM− lymphocytes. Furthermore, the proportion of MCAM+ CD4+ lymphocytes is significantly increased in the blood and in the central nervous system of patients with multiple sclerosis and experimental autoimmune encephalomyelitis animals compared with healthy controls or other neurological diseases, and MCAM expression is upregulated at the blood–brain barrier within inflammatory lesions. Moreover, blockade of MCAM or depletion of MCAM+ CD4+ T lymphocytes both restrict the migration of TH17 lymphocytes across blood–brain barrier endothelial cells and decrease the severity of experimental autoimmune encephalomyelitis. Our findings indicate that MCAM could serve as a potential biomarker for multiple sclerosis and represents a valuable target for the treatment of neuroinflammatory conditions. [ABSTRACT FROM AUTHOR]

NKG2D is an activating or coactivating receptor expressed on human natural killer (NK) cells, CD8+ T cells, and γ/δ T cells. NKG2D ligands have been detected on many tumor cell types and can be induced on nontransformed cells by environmental signals including DNA damage and inflammation. We investigated the contribution of NKG2D--NKG2D ligand interaction on CNS-directed immune responses. We observed that primary cultures of human adult oligodendrocytes and fetal astrocytes expressed ligands for NKG2D in vitro whereas neurons, microglia, and adult astrocytes did not. Disruption of the NKG2D--NKG2D ligand interaction using blocking antibodies significantly inhibited killing of primary human oligodendrocytes mediated by activated human NK cells, γ/δ T cells, and allo-reactive CD8+ T cells. NKG2D ligands [major histocompatibility complex class I chain-related molecules A and B (MICA/B)] were detected in groups of cells and colocalized with an oligodendrocyte marker (adenomatous polyposis coli) in white matter sections obtained from multiple sclerosis lesions but not in normal control samples. CD8+ T cells could be detected in close proximity to MICA/B+ cells within multiple sclerosis lesions, supporting an in vivo interaction between these immune effectors and stressed MICA/B-expressing oligodendrocytes. These results imply that NKG2D--NKG2D ligand interaction can potentially contribute to cytotoxic responses mediated by activated immune effector cells in the inflamed CNS, as observed in multiple sclerosis. [ABSTRACT FROM AUTHOR]