Howe, Charles L.

Abstract Neuromyelitis optica is an autoimmune inflammatory disorder targeting aquaporin-4 water channels in CNS astrocytes. Histopathological descriptions of astrocytic lesions reported in neuromyelitis optica so far have emphasized a characteristic loss of aquaporin-4, with deposition of IgG and complement and lysis of astrocytes, but sublytic reactions have been underappreciated. We performed a multi-modality study of 23 neuromyelitis optica autopsy cases (clinically and/or pathologically confirmed; 337 tissue blocks). By evaluating astrocytic morphology, immunohistochemistry and AQP4 RNA transcripts, and their associations with demyelinating activity, we documented a spectrum of astrocytopathy in addition to complement deposition, microglial reaction, granulocyte infiltration and regenerating activity. Within advanced demyelinating lesions, and in periplaque areas, there was remarkable hypertrophic astrogliosis, more subtle than astrocytic lysis. A degenerative component was suggested by ‘dystrophic’ morphology, cytoplasmic vacuolation, Rosenthal fibres and associated stress protein markers. The abundance of AQP4 mRNA transcripts in sublytic reactive astrocytes devoid of aquaporin-4 protein supported in vivo restoration following IgG-induced aquaporin-4 endocytosis/degradation. Astrocytic alterations extending beyond demyelinating lesions speak to astrocytopathy being an early and primary event in the evolving neuromyelitis optica lesion. Focal astrocytopathy observed without aquaporin-4 loss or lytic complement component deposition verifies that astrocytic reactions in neuromyelitis optica are not solely dependent on IgG-mediated aquaporin-4 loss or lysis by complement or by IgG-dependent leucocyte mediators. We conclude that neuromyelitis optica reflects a global astrocytopathy, initiated by binding of IgG to aquaporin-4 and not simply definable by demyelination and astrocytic lysis. The spectrum of astrocytic morphological changes in neuromyelitis optica attests to the complexity of factors influencing the range of astrocytic physiological responses to a targeted attack by aquaporin-4-specific IgG. Sublytic astrocytic reactions are no doubt an important determinant of the lesion’s evolution and potential for repair. Pharmacological manipulation of the astrocytic stress response may offer new avenues for therapeutic intervention.

Natural killer cells (NKC) and cytotoxic T lymphocytes (CTL) express NKG2D, a lectin‐like molecule that serves as a direct stimulatory receptor in the innate immune system and as a co‐stimulatory receptor in the adaptive system. In mice, the ligands for NKG2D are stress‐inducible molecules such as Rae‐1, H‐60 and MULT‐1. These MHC class I‐like molecules are generally absent in normal tissues but are upregulated by inflammation and virus infection. We have found that acute intracerebral infection with the Theiler's murine encephalomyelitis virus (TMEV) elicits robust infiltration of NKG2D‐positive CTL and NKC into the brain coincident with the zenith and resolution of viral load. Likewise, using quantitative RT‐PCR we found that MULT‐1 was upregulated coincident with the peak of viral load while Rae‐1 (only epsilon and delta tested) and H‐60 remained undetectable. Therefore, we hypothesized that CTL and NKC recognition of MULT‐1 on neurons is required for efficient viral clearance. However, in vivo immunodepletion of NKC and CTL beginning one day prior to infection and continuing throughout the first 3 weeks postinfection did not prevent efficient viral clearance despite greater than 90% reduction in NKG2D‐positive cells in the brain immune infiltrate as assessed by flow cytometry. Thus, the role of MULT‐1 expression following TMEV infection remains unclear and experiments are ongoing to determine the cellular locus of MULT‐1 expression and recognition. This work was supported by grant RG3636 from the National Multiple Sclerosis Society and by Donald and Frances Herdrich.

Stress‐dependent regulation of the immune response is a general repair and maintenance system. Members of the MHC class I superfamily serve as indicators of cellular stress. Nonclassical class I molecules such as H60, MULT‐1 and the RAE‐1 family are generally absent in normal tissues. We found that intracerebral infection with TMEV upregulated expression of these stress‐response molecules in the brain at timepoints that coincided with the control of viral load. Moreover, we found that about 50% of the brain‐ infiltrating cytotoxic T cells (CTLs) specific for the TMEV peptide VP2121–130 were positive for the NKG2D activating receptor at 7 days postinfection. NKG2D binds to RAE‐1, H60, and MULT‐1 and costimulates CTLs. When we blocked NKG2D using the CX5 function blocking antibody we found a significant increase in viral load in the brain. Therefore, we hypothesize that cellular stress associated with viral infection induces NKG2D ligand expression on target cells that in turn costimulates NKG2D‐bearing VP2‐specific CTLs to promote viral clearance. Our study may ultimately impact the health of people at risk from encephalitis and neurologic complications associated with picornaviral infections and may provide new ways to promote viral clearance in individuals suffering from persistent virus infections of the brain.

Objective This study was undertaken to describe a novel biomarker of germ cell tumor and associated paraneoplastic neurological syndrome (PNS). Methods Archival sera from patients with germ cell tumor–associated PNS were evaluated. We identified a common autoantigen in a human testicular cancer cell line (TCam‐2) by Western blot and mass spectrometry. Its identity was confirmed by recombinant‐protein Western blot, enzyme‐linked immunosorbent assay (ELISA), and cell‐based assay. Autoantibody specificity was confirmed by analyzing assorted control sera/cerebrospinal fluid. Results Leucine zipper 4 (LUZP4)–immunoglobulin G (IgG) was detected in 28 patients' sera, 26 of whom (93%) were men. The median age at neurological symptom onset was 45 years (range = 28–84). Median titer (ELISA) was 1:300 (1:50 to >1:6,400, normal value < 1:50). Coexistent kelchlike protein 11–IgG was identified in 18 cases (64%). The most common presenting phenotype was rhombencephalitis (17/28, 61%). Other presentations included limbic encephalitis (n = 5, 18%), seizures and/or encephalitis (n = 2, 7%), and motor neuronopathy/polyradiculopathy (n = 4, 14%). The most common malignancy among cancer‐evaluated PNS patients was seminoma (21/27, 78%). Nine of the 21 seminomas detected by whole‐body fluorodeoxyglucose positron emission tomography scan (43%) were extratesticular. Both female patients had ovarian teratoma. Regressed testicular germ cell tumors were found in 4 patients. Exposure of T‐cell–dendritic‐cell cocultures from chronic immunosuppression‐naïve LUZP4‐IgG–seropositive patients to recombinant LUZP4 protein evoked a marked increase in CD69 expression on both CD4+ and CD8+ T cells when compared to vehicle‐exposed and healthy control cultures. Interpretation LUZP4‐IgG represents a novel serological biomarker of PNS and has high predictive value for germ cell tumors. The demonstrated antigen‐specific T‐cell responses support a CD8+ T‐cell–mediated cytotoxic paraneoplastic and antitumor potential. ANN NEUROL 2021;89:1001–1010

We previously applied Systematic Evolution of Ligands by EXponential enrichment (SELEX) technology to identify myelin-specific DNA aptamers, using crude mouse central nervous system myelin as bait. This selection identified a 40-nucleotide aptamer (LJM-3064). Multiple biotinylated LJM-3064 molecules were conjugated to a streptavidin core to mimic a multimeric immunoglobulin M (IgM) antibody, generating 3064-BS-streptavidin (Myaptavin-3064). We previously showed that Myaptavin-3064 induces remyelination in the Theiler’s murine encephalomyelitis virus (TMEV) model of chronic spinal cord demyelination. While details of target binding and the mechanism of action remain unclear, we hypothesized that Myaptavin-3064 induces remyelination by binding to oligodendrocytes (OLs). We now report the results of binding assays using the human oligodendroglioma (HOG) cell line, applying both flow cytometry and immunocytochemistry (IC) to assay aptamer conjugate binding to cells. IC assays were applied to compare aptamer conjugate binding to primary embryonic mouse mixed cortical cultures and primary adult rat mixed glial cultures. We show that Myaptavin-3064 binds to HOG cells, with increased binding upon differentiation. In contrast, a negative control aptamer conjugate, 3060-BS, which did not promote central nervous system (CNS) remyelination, does not bind to HOG cells. Myaptavin-3064 did not bind to lung (L2) or kidney (BHK) cell lines. Total internal reflection fluorescence (TIRF) imaging indicates that Myaptavin-3064 binds at the cell membrane of live cells. In addition to HOG cells, Myaptavin-3064 binds to adult rat OLs, but not to embryonic mouse mixed cortical cultures. These data support the hypothesis that Myaptavin-3064 binds to a surface molecule on both rodent and human OLs in a manner that triggers a remyelination signal pathway.

ObjectiveWe recently reported successful treatment of a child with febrile infection‐related epilepsy syndrome (FIRES), a subtype of new onset refractory status epilepticus, with the recombinant interleukin‐1 (IL1) receptor antagonist (IL1RA) anakinra. On this basis, we tested whether endogenous IL1RA production or function is deficient in FIRES patients.MethodsLevels of IL1β and IL1RA were measured in serum and cerebrospinal fluid (CSF). The inhibitory activity of endogenous IL1RA was assessed using a cell‐based reporter assay. IL1RN gene variants were identified by sequencing. Expression levels for the secreted and intracellular isoforms of IL1RA were measured in patient and control cells by real‐time polymerase chain reaction.ResultsLevels of endogenous IL1RA and IL1β were elevated in the serum and CSF of patients with FIRES (n = 7) relative to healthy controls (n = 10). Serum from FIRES patients drove IL1R signaling activity and potentiated IL1R signaling in response to exogenous IL1β in a cell‐based reporter assay. Functional assessment of endogenous IL1RA activity in 3 FIRES patients revealed attenuated inhibition of IL1R signaling. Sequencing of IL1RN in our index patient revealed multiple variants. This was accompanied by reduced expression of intracellular but not secreted isoforms of IL1RA in the patient's peripheral blood mononuclear cells.InterpretationOur findings suggest that FIRES is associated with reduced expression of intracellular IL1RA isoforms and a functional deficiency in IL1RA inhibitory activity. These observations may provide insight into disease pathogenesis for FIRES and other inflammatory seizure disorders and may provide a valuable biomarker for therapeutic decision‐making. Ann Neurol 2019;85:526–537

SummaryObjectivesAlthough secondary hemophagocytic lymphohistiocytosis (HLH) has been reported in children with critical illness of various etiologies, it has not been reported in patients with febrile infection–related epilepsy syndrome (FIRES). We describe a series of patients with concurrent HLH and FIRES in an effort to establish common pathophysiologic abnormalities.MethodsFive patients with FIRES who were assessed for HLH were identified from a neurocritical care database. All were previously healthy and had extensive diagnostic testing. All had clinical deterioration with multiorgan dysfunction prompting HLH screening 20‐29 days after hospitalization. Markers for inflammatory dysregulation were assessed in cerebrospinal fluid (CSF) and serum at various time points. Outcomes were assessed 6 months after presentation.ResultsThree patients met clinical criteria for secondary HLH. Elevation of specific cytokines/chemokines was variable. CSF neopterin, high mobility group box 1 (HMGB1), and C‐X‐C motif chemokine ligand 8 (CXCL8) were significantly elevated in all. Interleukin‐1β (IL‐1β) and IL‐18 were not elevated in any of the samples. Treatment and outcomes were variable.SignificanceWe describe 3 patients with HLH and FIRES. The co‐occurrence of these 2 rare disorders suggests the possibility of a common immune dysregulation phenotype prolonging epileptogenesis. HLH screening in critically ill patients with FIRES may yield a broader understanding of shared inflammatory processes.