SARS-CoV-2 infects epithelial cells of the blood-cerebrospinal fluid barrier rather than endothelial cells or pericytes of the blood-brain barrier.

BACKGROUND: As a consequence of SARS-CoV-2 infection various neurocognitive and neuropsychiatric symptoms can appear, which may persist for several months post infection. However, cell type-specific routes of brain infection and underlying mechanisms resulting in neuroglial dysfunction are not well understood. METHODS: Here, we investigated the susceptibility of cells constituting the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) of the choroid plexus (ChP) to SARS-CoV-2 infection using human induced pluripotent stem cell (hiPSC)-derived cellular models and a ChP papilloma-derived epithelial cell line as well as ChP tissue from COVID-19 patients, respectively. RESULTS: We noted a differential infectibility of hiPSC-derived brain microvascular endothelial cells (BMECs) depending on the differentiation method. Extended endothelial culture method (EECM)-BMECs characterized by a complete set of endothelial markers, good barrier properties and a mature immune phenotype were refractory to SARS-CoV-2 infection and did not exhibit an activated phenotype after prolonged SARS-CoV-2 inoculation. In contrast, defined medium method (DMM)-BMECs, characterized by a mixed endothelial and epithelial phenotype and excellent barrier properties were productively infected by SARS-CoV-2 in an ACE2-dependent manner. hiPSC-derived brain pericyte-like cells (BPLCs) lacking ACE2 expression were not susceptible to SARS-CoV-2 infection. Furthermore, the human choroid plexus papilloma-derived epithelial cell line HIBCPP, modeling the BCSFB was productively infected by SARS-CoV-2 preferentially from the basolateral side, facing the blood compartment. Assessment of ChP tissue from COVID-19 patients by RNA in situ hybridization revealed SARS-CoV-2 transcripts in ChP epithelial and ChP stromal cells. CONCLUSIONS: Our study shows that the BCSFB of the ChP rather than the BBB is susceptible to direct SARS-CoV-2 infection. Thus, neuropsychiatric symptoms because of COVID-19 may rather be associated with dysfunction of the BCSFB than the BBB. Future studies should consider a role of the ChP in underlying neuropsychiatric symptoms following SARS-CoV-2 infection.

Gut microbiota-specific IgA+ B cells traffic to the CNS in active multiple sclerosis.

Changes in gut microbiota composition and a diverse role of B cells have recently been implicated in multiple sclerosis (MS), a central nervous system (CNS) autoimmune disease. Immunoglobulin A (IgA) is a key regulator at the mucosal interface. However, whether gut microbiota shape IgA responses and what role IgA+ cells have in neuroinflammation are unknown. Here, we identify IgA-bound taxa in MS and show that IgA-producing cells specific for MS-associated taxa traffic to the inflamed CNS, resulting in a strong, compartmentalized IgA enrichment in active MS and other neuroinflammatory diseases. Unlike previously characterized polyreactive anti-commensal IgA responses, CNS IgA cross-reacts with surface structures on specific bacterial strains but not with brain tissue. These findings establish gut microbiota-specific IgA+ cells as a systemic mediator in MS and suggest a critical role of mucosal B cells during active neuroinflammation with broad implications for IgA as an informative biomarker and IgA-producing cells as an immune subset to harness for therapeutic interventions.

Peripheral neuropathy in antineutrophil cytoplasmic antibody-associated vasculitides: Insights from the DCVAS study.

OBJECTIVE: Reported prevalence of vasculitic neuropathy (VN) in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is highly variable, and associations with other organ manifestations have not been studied systematically while accounting for diagnostic certainty of VN. METHODS: Data of all patients with AAV within the Diagnostic and Classification criteria for primary systemic VASculitis study were analyzed cross-sectionally. VN was categorized as definite (histology proven), probable (multiple mononeuropathy or nerve biopsy consistent with vasculitis), or possible (all others). Associations with other organ manifestations were compared in patients with and without VN. RESULTS: Nine hundred fifty-five patients (mean age 57 years, range 18-91 years, 51% female) were identified. Of these, 572 had granulomatosis with polyangiitis (GPA), 218 microscopic polyangiitis (MPA), and 165 eosinophilic granulomatosis with polyangiitis (EGPA). The prevalence of VN was 65% in EGPA, 23% in MPA, and 19% in GPA. Nerve biopsy was performed in 32/269 (12%) patients, demonstrating definite vasculitis in 17/32 (53%) of patients. VN was associated with myeloperoxidase-ANCA positivity (p = 0.004) and skin (p < 0.001), musculoskeletal, (p < 0.001) and cardiovascular (p = 0.005) involvement. Patients with VN were less likely to have renal (p < 0.001), eye (p < 0.001), and gastrointestinal (p = 0.023) involvement. CONCLUSIONS: Our study provides comprehensive insights into the prevalence and organ associations of VN in a large, systematically collected AAV cohort. VN is most commonly associated with skin, musculoskeletal, and cardiovascular manifestations. In routine clinical practice, diagnosis of VN is infrequently confirmed by the gold standard of nerve biopsy but rather supported by the clinical setting of active systemic AAV.

Association of antibodies against myelin and neuronal antigens with neuroinflammation in systemic lupus erythematosus.

OBJECTIVES: To determine frequency and syndrome specificity of novel and known nervous system (NS)-directed antibodies in a large, unbiased cohort of SLE patients in the Swiss SLE Cohort Study. METHODS: This retrospective pilot study included 174 patients in a cross-sectional and 102 in a longitudinal study. Antibodies against 12 NS antigens [myelin oligodendrocyte glycoprotein (MOG), neurofascin 186 (NF186), aquaporin-4 (AQP4), N-methyl-D-aspartate receptor (subunit NR1) (NMDAR-NR1), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (subunits 1 and 2) (AMPAR1/2), gamma-aminobutyric acid B receptor (subunits B1 and B2) (GABABR1/2), glutamate decarboxylase 65 (GAD65), glycine receptor (GlyR), contactin-associated protein-like 2 (CASPR2), leucine-rich glioma-inactivated 1 (LGI1), metabotropic glutamate receptor 5 (mGluR5) and dipeptidyl-peptidase-like protein 6 (DPPX)] were screened with validated cell-based assays and correlated with clinical and diagnostic findings. RESULTS: Twenty-three of one hundred and seventy-four (13.2%) patients harboured antibodies against MOG (n = 14), NF186 (n = 6), GAD65 (n = 2), AQP4 and GlyR (n = 1). Anti-MOG antibodies were most frequently found in the cohort (8%). Thirteen of the anti-NS antibody-positive patients showed clinical symptoms of NS involvement, a subgroup of which (n = 8) resembled the syndrome associated with the antibody. Nine patients harboured antibodies without neurological symptoms and one patient was lost to follow-up. The frequency of NPSLE was significantly higher in the anti-NS antibody-positive patients (13/23, 56.5%: MOG 6/14, 42.9%; NF186 5/6, 83.3%; GAD65 2/2, 100%; AQP4/GlyR 0/1, 0%) compared with the antibody-negative cohort (21/151, 13.9%) (chi-square test, P < 0.0001). CONCLUSION: Anti-NS antibodies, most prevalently anti-MOG antibodies, are significantly associated with NPSLE and manifest with the distinct neurological syndrome associated with the antibody in a subgroup. Follow-up studies in large, independent cohorts will reveal whether these anti-NS antibodies could serve as a diagnostic and prognostic biomarker for NPSLE and enable tailored treatment decisions in this challenging and diverse patient cohort.

Humoral autoimmunity in multiple sclerosis.

The important role of B cells and autoantibodies in the pathogenesis of MS is increasingly appreciated. The recruitment and maintenance of B cells and plasma cells in MS lesions is presumably based on local production of lymphoid chemokines and B cell activation factor of the TNF family (BAFF). The failure of the clinical trial with Atacicept targeting BAFF and its relative APRIL was a great surprise and cannot readily be explained. A role for BAFF in CNS physiology, e.g. via targeting of the Nogo-66 receptor might have to be considered. The identification of patient subgroups based on autoantibodies is a future challenge. Currently patients with neuromyelitis optica (NMO) can be identified by antibodies to aquaporin 4 and about a third of children with acquired demyelinating diseases have antibodies against conformationally correct MOG, while such antibodies are hardly found in adult MS patients. Searching for new targets of the autoimmune response in adult MS patients, we have identified two axo-glial proteins focused around the node of Ranvier, namely neurofascin and contactin-2/TAG-1. Testing the functional relevance of such an autoimmune response in animal models revealed that antibodies to neurofascin may induce axonal injury and that T cells specific for contactin-2/TAG-1 mediate preferentially gray matter injury.