Ute-Christiane Meier

Shared Alterations in NK Cell Frequency, Phenotype, and Function in Chronic Human Immunodeficiency Virus and Hepatitis C Virus Infections

ABSTRACT Human immunodeficiency virus (HIV) and hepatitis C virus (HCV) cause clinically important persistent infections. The effects of virus persistence on innate immunity, including NK cell responses, and the underlying mechanisms are not fully understood. We examined the frequency, phenotype, and function of peripheral blood CD3− CD56+ NK subsets in HIV+ and HCV+ patients and identified significantly reduced numbers of total NK cells and a striking shift in NK subsets, with a marked decrease in the CD56dim cell fraction compared to CD56bright cells, in both infections. This shift influenced the phenotype and functional capacity (gamma interferon production, killing) of the total NK pool. In addition, abnormalities in the functional capacity of the CD56dim NK subset were observed in HIV+ patients. The shared NK alterations were found to be associated with a significant reduction in serum levels of the innate cytokine interleukin 15 (IL-15). In vitro stimulation with IL-15 rescued NK cells of HIV+ and HCV+ patients from apoptosis and enhanced proliferation and functional activity. We hypothesize that the reduced levels of IL-15 present in the serum during HIV and HCV infections might impact NK cell homeostasis, contributing to the common alterations of the NK pool observed in these unrelated infections.

Cytotoxic T Lymphocyte Lysis Inhibited by Viable HIV Mutants

Immune evasion by the human immunodeficiency virus (HIV) is unexplained but may involve the mutation of viral antigens. When cytotoxic T lymphocytes engaged CD4-positive cells that were acutely infected with HIV bearing natural variant epitopes in reverse transcriptase, substantial inhibition of specific antiviral lysis was observed. Mutant viruses capable of these transactive effects could facilitate the persistence of a broad range of HIV variants in the face of an active and specific immune response.

Association of innate immune activation with latent Epstein-Barr virus in active MS lesions

Objective: To determine whether the activation of innate immune responses, which can be elicited by pathogenic and endogenous triggers, is associated with the presence of Epstein-Barr virus (EBV) infection in the multiple sclerosis (MS) brain. Methods: White matter postmortem MS (n = 10) and control tissue (n = 11) was analyzed for the expression of the proinflammatory cytokine interferon α (IFNα) by immunohistochemistry and for EBV by using the highly sensitive method of EBV-encoded RNA (EBER) in situ hybridization. Results: We detected overexpression of IFNα in active areas of white matter MS lesions but not in inactive MS lesions, normal-appearing white matter, or normal brains. The presence of IFNα in macrophages and microglia (expressing human leukocyte antigen class II) is suggestive of local production as part of an acute inflammatory process. Interestingly, EBERs were also specifically detected in areas where IFNα was overexpressed in these preselected active MS lesions. EBER+ cells were also found in CNS lymphoma and stroke cases, but were absent in other control brains. We next addressed a potential mechanism, e.g., the role of EBERs in eliciting IFNα production, and transfected EBERs into human embryonic kidney (HEK) cells. We used HEK cells that stably expressed Toll-like receptor-3, which recognizes double-stranded RNAs, associated with many viral infections. EBERs elicited IFNα production in vitro. Conclusion: These findings suggest that latent EBV infection may contribute to the inflammatory milieu in active MS lesions by activating innate immune responses, e.g., IFNα production. Unraveling the underlying mechanisms may help in uncovering causal pathways and developing better treatment strategies for MS and other neuroinflammatory diseases.

A novel approach to antigen-specific deletion of CTL with minimal cellular activation using alpha3 domain mutants of MHC class I/peptide complex.

In this study, we have compared the effector functions and fate of a number of human CTL clones in vitro or ex vivo following contact with variant peptides presented either on the cell surface or in a soluble multimeric format. In the presence of CD8 coreceptor binding, there is a good correlation between TCR signaling, killing of the targets, and FasL-mediated CTL apoptosis. Blocking CD8 binding using alpha3 domain mutants of MHC class I results in much reduced signaling and reduced killing of the targets. Surprisingly, however, FasL expression is induced to a similar degree on these CTLs, and apoptosis of CTL is unaffected. The ability to divorce these events may allow the deletion of antigen-specific and pathological CTL populations without the deleterious effects induced by full CTL activation.

Cell death pathways and autophagy in the central nervous system and its involvement in neurodegeneration, immunity and central nervous system infection: to die or not to die – that is the question

Death rules our lives. In this short paper, we summarize new insights into molecular mechanisms of neurodegeneration. Here we review the most important processes of cell death: apoptosis and oncosis. We focus on autophagy, which is pivotal for neuronal homeostasis, in the context of neurodegeneration, infection and immunity. Its dysfunction has been linked to several neurodegenerative diseases such as Parkinsons, Huntingtons and Alzheimers diseases. Our understanding is still incomplete, but may highlight attractive new avenues for the development of treatment strategies to combat neurodegenerative diseases.

Translational Mini-Review Series on B cell subsets in disease. B cells in multiple sclerosis: drivers of disease pathogenesis and Trojan horse for Epstein–Barr virus entry to the central nervous system?

OTHER ARTICLES PUBLISHED IN THIS MINI‐REVIEW SERIES ON B CELL SUBSETS IN DISEASE

Th1 polarization of CD4+ T cells by Toll-like receptor 3-activated human microglia.

Abstract Toll-like receptors (TLRs) are expressed by human microglia and translate environmental cues into distinct activation programs. We addressed the impact of TLR ligation on the capacity of human microglia to activate and polarize CD4+ T cell responses. As microglia exist under distinct states of activation, we examined both ramified and ameboid microglia isolated from adult and fetal CNS, respectively. In vitro, ligation of TLR3 significantly increased major histocompatibility complex and costimulatory molecule expression on adult microglia and induced high levels of interferon-α, interleukin-12p40, and interleukin-23. TLR4 and, in particular, TLR2 had a more limited capacity to induce such responses. Coculturing allogeneic CD4+ T cells with microglia preactivated with TLR3 did not increase T cell proliferation above basal levels but consistently led to elevated levels of interferon-γ secretion and Th1 polarization. Fetal microglial TLR3 responses were comparable; in contrast, TLR2 and TLR4 decreased major histocompatibility complex class II expression on fetal cells and reduced CD4+ T cell proliferation to levels below those found in untreated cocultures. All 3 TLRs induced comparable interleukin-6 secretion by microglia. Our findings illustrate how activation of human microglia via TLRs, particularly TLR3, can change the profile of local CNS immune responses by translating Th1 polarizing signals to CD4+ T cells.

Viral pathophysiology of multiple sclerosis: A role for Epstein-Barr virus infection?

Abstract Multiple sclerosis (MS) is the most common inflammatory demyelinating and degenerative disease of the CNS. The cause of MS is unknown but environmental risk factors are implicated in MS. Several viruses have been proposed as a trigger for MS, and lately Epstein-Barr virus (EBV) has become the leading candidate. An infectious aetiology fits with a number of epidemiological observations in addition to the immunopathological features of the disease. In this review we will summarize the emerging evidence, which demonstrates a strong association between EBV infection and MS. The conundrum remains as to whether EBV is directly involved in the pathophysiology of MS, or alternatively if the immunopathology of MS somehow affects the regulation of EBV infection.

Disposable MMP-9 sensor based on the degradation of peptide cross- linked hydrogel films using electrochemical impedance spectroscopy

Matrix metalloproteinase-9 (MMP-9) plays an important role in both physiological and pathological processes. This enzyme is a peripheral biomarker of neuroinflammation in multiple sclerosis (MS), a chronic autoimmune disease of the central nervous system. Presently, expensive magnetic resonance imaging (MRI) studies are used to monitor subclinical disease activity in MS. An alternative to costly MRI scans could be the detection of MMP-9, using a low-cost, disposable sensor system for MMP-9 suitable for home-monitoring of inflammation. This would allow an early prediction of the failure of anti-inflammatory therapies and more timely clinical intervention to limit neuronal damage and prevent disability. Herein we present the development of a disposable sensor for fast and straightforward detection of MMP-9. Biosensors were produced by coating electrodes with oxidized dextran and subsequent cross-linking with peptides containing specific cleavage sites for MMP-9. Exposure of the films to the enzyme resulted in the degradation of the films, which was monitored using impedance measurements. Sensor response was rapid, a significant impedance change was usually observed within 5 min after the addition of MMP-9. Sensors showed a negligible response to matrix metalloproteinase-2 (MMP-2), a protease which may interfere with MMP-9 detection. The peptide sequence with the highest sensitivity and selectivity Leu-Gly-Arg-Met-Gly-Leu-Pro-Gly-Lys was selected to construct calibration curves. MMP-9 was successfully detected in a clinically relevant range from 50 to 400 ng/ml. Two different processes of hydrogel degradation were observed on electrode surfaces with different roughness, and both appeared suitable to monitor MMP-9 activity. The sensor materials are generic and can be easily adopted to respond to other proteases by selecting peptide cross-linkers with suitable cleavage sites.

Hypovitaminosis-D and EBV: no interdependence between two MS risk factors in a healthy young UK autumn cohort.

Late Epstein-Barr virus infection and hypovitaminosis-D as environmental risk factors in the pathogenesis of multiple sclerosis are gaining great interest. We, therefore, tested for in-vivo interdependence between Epstein-Barr-virus (EBV)-status and 25-hydroxyvitamin D3 (25(OH)D3) -level in healthy young individuals from a United Kingdom (UK) autumn cohort. EBV-load was measured by quantitative polymerase chain reaction and 25(OH)D3 levels by isotope-dilution liquid chromatography-tandem mass spectrometry. This young, healthy UK autumn cohort showed surprisingly low levels of 25(OH)D3 (mean value: 40.5 nmol/L ± 5.02). Furthermore, we found that low 25(OH)D3 levels did not impact on EBV load and anti-EBV nuclear antigen-1 (EBNA-1) titers. However, we observed a correlation between EBV load and EBNA-1 titers. These observations should be of value in the study of the potential relationship between hypovitaminosis-D and EBV-status in the pathophysiology of multiple sclerosis.