African Americans Have Differences in CSF Soluble TREM2 and Associated Genetic Variants.

OBJECTIVE: To evaluate for racial differences in triggering receptor expressed on myeloid cells 2 (TREM2), a key immune mediator in Alzheimer disease, the levels of CSF soluble TREM2 (sTREM2), and the frequency of associated genetic variants were compared in groups of individuals who self-reported their race as African American (AA) or non-Hispanic White (NHW). METHODS: Community-dwelling older research participants underwent measurement of CSF sTREM2 concentrations and genetic analyses. RESULTS: The primary cohort included 91 AAs and 868 NHWs. CSF sTREM2 levels were lower in the AA compared with the NHW group (1,336 ± 470 vs 1,856 ± 624 pg/mL, p < 0.0001). AAs were more likely to carry TREM2 coding variants (15% vs 3%, p < 0.0001), which were associated with lower CSF sTREM2. AAs were less likely to carry the rs1582763 minor allele (8% vs 37%, p < 0.0001), located near MS4A4A, which was associated with higher CSF sTREM2. These findings were replicated in an independent cohort of 23 AAs and 917 NHWs: CSF sTREM2 levels were lower in the AA group (p = 0.03), AAs were more likely to carry coding TREM2 variants (22% vs 4%, p = 0.002), and AAs were less likely to carry the rs1582763 minor allele (16% vs 37%, p = 0.003). CONCLUSIONS: On average, AAs had lower CSF sTREM2 levels compared with NHWs, potentially because AAs are more likely to carry genetic variants associated with lower CSF sTREM2 levels. Importantly, CSF sTREM2 reflects TREM2-mediated microglial activity, a critical step in the immune response to amyloid plaques. These findings suggest that race may be associated with risk for genetic variants that influence Alzheimer disease-related inflammation.

B cell antigen presentation is sufficient to drive neuroinflammation in an animal model of multiple sclerosis.

B cells are increasingly regarded as integral to the pathogenesis of multiple sclerosis, in part as a result of the success of B cell-depletion therapy. Multiple B cell-dependent mechanisms contributing to inflammatory demyelination of the CNS have been explored using experimental autoimmune encephalomyelitis (EAE), a CD4 T cell-dependent animal model for multiple sclerosis. Although B cell Ag presentation was suggested to regulate CNS inflammation during EAE, direct evidence that B cells can independently support Ag-specific autoimmune responses by CD4 T cells in EAE is lacking. Using a newly developed murine model of in vivo conditional expression of MHC class II, we reported previously that encephalitogenic CD4 T cells are incapable of inducing EAE when B cells are the sole APC. In this study, we find that B cells cooperate with dendritic cells to enhance EAE severity resulting from myelin oligodendrocyte glycoprotein (MOG) immunization. Further, increasing the precursor frequency of MOG-specific B cells, but not the addition of soluble MOG-specific Ab, is sufficient to drive EAE in mice expressing MHCII by B cells alone. These data support a model in which expansion of Ag-specific B cells during CNS autoimmunity amplifies cognate interactions between B and CD4 T cells and have the capacity to independently drive neuroinflammation at later stages of disease.

Predicting optimal response to B-cell depletion with rituximab in multiple sclerosis using CXCL13 index, magnetic resonance imaging and clinical measures.

BACKGROUND: B-cell depleting drugs show promise for treating multiple sclerosis. OBJECTIVE: We sought predictors of optimal response to rituximab, a B-cell depleting antibody, to help guide therapy selection. METHODS: We performed a post hoc study of 30 relapsing multiple sclerosis patients with breakthrough disease while on beta-interferon or glatiramer acetate who were treated with add-on rituximab. Standardized neurologic examinations, brain magnetic resonance imaging, and cerebrospinal fluid were obtained before and after rituximab. Tissue biomarkers were measured. Optimal responders were defined as having no evidence of disease activity. RESULTS: At baseline, optimal responders with no evidence of disease activity had higher IgG indices (P = 0.041), and higher CXCL13 indices ((cerebrospinal fluid CXCL13/serum CXCL13)/albumin index; P = 0.024), more contrast enhancing lesions (P = 0.002), better 25 foot timed walk (P = 0.001), and Expanded Disability Status Scale (P = 0.002). Rituximab treatment led to reduced cerebrospinal fluid biomarkers of tissue destruction: myelin basic protein (P = 0.046), neurofilament light chain (P < 0.001), and of inflammation (CXCL13 index; P = 0.042). CONCLUSIONS: Multiple sclerosis patients with optimal response to rituximab had higher cerebrospinal fluid IgG and CXCL13 indices, more gadolinium-enhancing lesions, and less disability at baseline. Rituximab treatment led to decreased markers of inflammation and tissue damage. If validated, these results will help identify multiple sclerosis patients who will respond optimally to B-cell depletion.

CXCL13 is a biomarker of inflammation in multiple sclerosis, neuromyelitis optica, and other neurological conditions.

CXCL13, a B-cell chemokine, has been proposed as a biomarker in a variety of conditions, some of which can mimic multiple sclerosis and can have very high levels. In this case-control study, cerebrospinal fluid (CSF) CXCL13 was elevated in multiple sclerosis, neuromyelitis optica and other inflammatory neurological controls compared with noninflammatory controls. Levels did not differentiate disease groups. For all subjects taken together, CSF CXCL13 correlated with CSF WBC, oligoclonal band numbers, CSF protein, EDSS, and neurofilament levels. In subgroup analyses, CSF CXCL13 correlated with CSF WBC in neuromyelitis optica and IgG index in multiple sclerosis. Additionally, serum CXCL13 was elevated in neuromyelitis optica.

Limited sufficiency of antigen presentation by dendritic cells in models of central nervous system autoimmunity.

Experimental autoimmune encephalomyelitis (EAE), a model for the human disease multiple sclerosis (MS), is dependent upon the activation and effector functions of autoreactive CD4 T cells. Multiple interactions between CD4 T cells and major histocompatibility class II (MHCII)+ antigen presenting cells (APCs) must occur in both the periphery and central nervous system (CNS) to elicit autoimmunity. The identity of the MHCII+ APCs involved throughout this process remains in question. We investigated which APC in the periphery and CNS mediates disease using transgenic mice with MHCII expression restricted to dendritic cells (DCs). MHCII expression restricted to DCs results in normal susceptibility to peptide-mediated EAE. Indeed, radiation-sensitive bone marrow-derived DCs were sufficient for all APC functions during peptide-induced disease. However, DCs alone were inefficient at promoting disease after immunization with the myelin protein myelin oligodendrocyte glycoprotein (MOG), even in the presence of MHCII-deficient B cells. Consistent with a defect in disease induction following protein immunization, antigen presentation by DCs alone was incapable of mediating spontaneous optic neuritis. These results indicate that DCs are capable of perpetuating CNS-targeted autoimmunity when antigens are readily available, but other APCs are required to efficiently initiate pathogenic cognate CD4 T cell responses.

B cells limit epitope spreading and reduce severity of EAE induced with PLP peptide in BALB/c mice.

The role of B cells and antibody in experimental autoimmune encephalomyelitis (EAE) appears to differ based on the identity and state (protein vs. encephalitogenic peptide) of the inducing antigen and the strain of mouse utilized. The involvement of B cells in the induction of EAE by peptides of proteolipid protein (PLP) in BALB/c mice was investigated. Wild-type and B cell-deficient (B cell-/-) mice on the BALB/c background were immunized with overlapping PLP peptides, and the disease course was followed. Although incidence and onset of PLP(180-199)-induced EAE was similar in WT and B cell-/- mice, the clinical course was more severe in B cell-/- mice. During acute disease, proliferation and interferon-gamma production by lymphoid cells from both strains were similar and were elicited predominantly in response to the immunizing antigen. However, during chronic disease lymphoid cells isolated from B cell-/- mice proliferated to a greater extent and produced more interferon-gamma in response to the overlapping peptide PLP185-206 and to the smaller internal peptide PLP185-199 than did WT mice. These data suggest that B cells regulate PLP-induced EAE in BALB/c mice through control of epitope spreading.