Autoantibody Encephalitis: Presentation, Diagnosis, and Management

G protein-coupled receptors related to autoimmunity in postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is characterized by exaggerated orthostatic tachycardia in the absence of orthostatic hypotension. The pathophysiology of POTS may involve hypovolemia, autonomic neuropathy, a hyperadrenergic state, and cardiovascular deconditioning, any of which can co-occur in the same patient. Furthermore, there is growing evidence of the role of autoimmunity in a subset of POTS cases. In recent years, investigators have described an increased rate of autoimmune comorbidities as evidenced by the finding of several types of neural receptor autoantibody and non-specific autoimmune marker in patients with POTS. In particular, the association of the disease with several types of anti-G protein-coupled receptor (GPCR) antibodies and POTS has frequently been noted. A previous study reported that autoantibodies to muscarinic AChRs may play an important role in POTS with persistent, gastrointestinal symptoms. To date, POTS is recognized as one of the sequelae of coronavirus disease 2019 (COVID-19) and its frequency and pathogenesis are still largely unknown. Multiple autoantibody types occur in COVID-related, autonomic disorders, suggesting the presence of autoimmune pathology in these disorders. Herein, we review the association of anti-GPCR autoantibodies with disorders of the autonomic nervous system, in particular POTS, and provide a new perspective for understanding POTS-related autoimmunity.

VH2+ Antigen-Experienced B Cells in the Cerebrospinal Fluid Are Expanded and Enriched in Pediatric Anti-NMDA Receptor Encephalitis

Pediatric and adult autoimmune encephalitis (AE) are often associated with Abs to the NR1 subunit of the N-methyl-d-aspartate (NMDA) receptor (NMDAR). Very little is known regarding the cerebrospinal fluid humoral immune profile and Ab genetics associated with pediatric anti-NMDAR-AE. Using a combination of cellular, molecular, and immunogenetics tools, we collected cerebrospinal fluid from pediatric subjects and generated 1) flow cytometry data to calculate the frequency of B cell subtypes in the cerebrospinal fluid of pediatric subjects with anti-NMDAR-AE and controls, 2) a panel of recombinant human Abs from a pediatric case of anti-NMDAR-AE that was refractory to treatment, and 3) a detailed analysis of the Ab genes that bound the NR1 subunit of the NMDAR. Ag-experienced B cells including memory cells, plasmablasts, and Ab-secreting cells were expanded in the pediatric anti-NMDAR-AE cohort, but not in the controls. These Ag-experienced B cells in the cerebrospinal fluid of a pediatric case of NMDAR-AE that was refractory to treatment had expanded use of variable H chain family 2 (VH2) genes with high somatic hypermutation that all bound to the NR1 subunit of the NMDAR. A CDR3 motif was identified in this refractory case that likely drove early stage activation and expansion of naive B cells to Ab-secreting cells, facilitating autoimmunity associated with pediatric anti-NMDAR-AE through the production of Abs that bind NR1. These features of humoral immune responses in the cerebrospinal fluid of pediatric anti-NMDAR-AE patients may be relevant for clinical diagnosis and treatment.

Biomarkers in autoimmune diseases of the central nervous system

The autoimmune diseases of the central nervous system (CNS) represent individual heterogeneity with different disease entities. Although clinical and imaging features make it possible to characterize larger patient cohorts, they may not provide sufficient evidence to detect disease activity and response to disease modifying drugs. Biomarkers are becoming a powerful tool due to their objectivity and easy access. Biomarkers may indicate various aspects of biological processes in healthy and/or pathological states, or as a response to drug therapy. According to the clinical features described, biomarkers are usually classified into predictive, diagnostic, monitoring and safety biomarkers. Some nerve injury markers, humoral markers, cytokines and immune cells in serum or cerebrospinal fluid have potential roles in disease severity and prognosis in autoimmune diseases occurring in the CNS, which provides a promising approach for clinicians to early intervention and prevention of future disability. Therefore, this review mainly summarizes the potential biomarkers indicated in autoimmune disorders of the CNS.

Autoimmune encephalitis after herpes simplex encephalitis: A still undefined condition

Herpes simplex encephalitis (HSE) is one of the most common sporadic viral encephalitis. Generally, HSE is characterized by a monophasic short course, although in some patients neurological relapses or worsening of deficits can develop some weeks later, when viral therapy has been discontinued and signs and symptoms of the central nervous system (CNS) damage seem to have stabilized. The second HSE stage is generally identified as autoimmune encephalitis after HSE (AEaHSE). Aim of this paper is to discuss which are the present knowledge in this regard. Literature analysis showed that AEaHSE exists, it is more common in younger children and it has different clinical manifestations according to age. All the patients with AEaHSE are positive for one or more neuronal cell-surface and synaptic antibodies, mainly anti-NMDAR antibodies, and the earlier the appearance of the antibodies the greater the risk of AEaHSE development. This means that a careful monitoring of antibody production starting from anti-NMDAR antibodies in all HSE cases could lead to the early identification of AEaHSE and the prompt administration of a potentially effective therapy. Further studies are needed to clarify which are the main pathogenetic mechanisms, whether there are differences in risk of development and clinical course of AEaHSE according to the type of antibody production, why response to immunosuppressive therapy significantly varies and whether administration of steroids to patients with HSE during the first phase of disease can play a role for reducing the risk of AEaHSE development.