Histamine Receptor H1 Signaling in Central Nervous System Autoimmmune Disease and Immune Deviation

Multiple Sclerosis (MS) is a demyelinating disorder of the central nervous system affecting 0.1% of the population in the Northern hemisphere. MS is a complex disease that depends on genetic and environmental factors and is controlled by multiple genes that exert a modest effect in the overall disease outcome. The complex nature of the disease complicates the study of individual genes and their contribution in the disease process. To investigate mechanisms underlying the development of diseases like MS and how disease course can be manipulated, animal models have been extensively used, with Experimental Allergic Encephalomyelitis (EAE) being the principle autoimmune model for MS. Even though EAE, like MS, is a complex disease and polygenic in nature, it can be reduced to monogenic intermediate or subphenotypes, which allows for identification of the causative gene and its mechanism. One such subphenotype of EAE in mice, Bordetella pertussis toxin-induced histamine sensitization (Bphs) is controlled by Hrh1, gene encoding mouse histamine receptor H1 (H1R), wherein sensitized animals of susceptible strains die upon histamine challenge and resistant strains do not. Moreover, mice deficient in H1R (H1RKO) show delayed onset and reduced severity in the clinical course of EAE. However, the mechanism by which H1R and its polymorphisms regulate EAE is unknown. As a disease susceptibility gene, Hrh1 could act in different cell types and at several checkpoints in the disease process. This includes endothelial cells that regulate blood-brain barrier, antigen presenting cells or T cells, which regulate the cytokine production. Using transgenic mice expressing H1R exclusively in T cells, this study shows that H1R expression in T cells is sufficient to restore the EAE severity and the disease associated cytokine production of H1RKO mice to wild type levels. H1R from susceptible and resistant strains of mice differ by three amino acids. The P-V-P haplotype (H1RS) is associated with disease susceptibility whereas the L-MS (H1RR) haplotype is associated with less severe disease. In this study, using transgenic mice, we show that reexpression of H1RS fully complements the clinical EAE and the disease-associated cytokine production of H1RKO mice to wild type levels, however, reexpression of H1RR fails to do so. These data suggest that H1RR is not functional relative to H1RS. Mechanistically, using 293T cells, we show that the two H1R alleles exhibit differential cell surface expression and altered intracellular trafficking, with the H1RR allele being retained within the endoplasmic reticulum (ER). Moreover, we show that all three residues (L-M-S) comprising the H1RR haplotype are required for altered expression. Thus, polymorphisms influencing cell surface expression of H1R regulate immune functions and autoimmune disease susceptibility

Beyond cDC1: Emerging Roles of DC Crosstalk in Cancer Immunity

Dendritic cells (DCs) efficiently process and present antigens to T cells, and by integrating environmental signals, link innate and adaptive immunity. DCs also control the balance between tolerance and immunity, and are required for T-cell mediated anti-tumor immunity. One subset of classical DCs, cDC1, are particularly important for eliciting CD8 T cells that can kill tumor cells. cDC1s are superior in antigen cross-presentation, a process of presenting exogenous antigens on MHC class I to activate CD8+ T cells. Tumor-associated cDC1s can transport tumor antigen to the draining lymph node and cross-present tumor antigens, resulting in priming and activation of cytotoxic T cells. Although cross-presenting cDC1s are critical for eliciting anti-tumor T cell responses, the role and importance of other DC subsets in anti-tumor immunity is not as well-characterized. Recent literature in other contexts suggests that critical crosstalk between DC subsets can significantly alter biological outcomes, and these DC interactions likely also contribute significantly to tumor-specific immune responses. Therefore, antigen presentation by cDC1s may be necessary but not sufficient for maximal immune responses against cancer. Here, we discuss recent advances in the understanding of DC subset interactions to maximize anti-tumor immunity, and propose that such interactions should be considered for the development of better DC-targeted immunotherapies

The induction of antibody production by IL-6 is indirectly mediated by IL-21 produced by CD4+ T cells

Interleukin (IL) 6 is a proinflammtory cytokine produced by antigen-presenting cells and nonhematopoietic cells in response to external stimuli. It was initially identified as a B cell growth factor and inducer of plasma cell differentiation in vitro and plays an important role in antibody production and class switching in vivo. However, it is not clear whether IL-6 directly affects B cells or acts through other mechanisms. We show that IL-6 is sufficient and necessary to induce IL-21 production by naive and memory CD4+ T cells upon T cell receptor stimulation. IL-21 production by CD4+ T cells is required for IL-6 to promote B cell antibody production in vitro. Moreover, administration of IL-6 with inactive influenza virus enhances virus-specific antibody production, and importantly, this effect is dependent on IL-21. Thus, IL-6 promotes antibody production by promoting the B cell helper capabilities of CD4+ T cells through increased IL-21 production. IL-6 could therefore be a potential coadjuvant to enhance humoral immunity

Selective Impairment of TH17-Differentiation and Protection against Autoimmune Arthritis after Overexpression of BCL2A1 in T Lymphocytes

The inhibition of apoptotic cell death in T cells through the dysregulated expression of BCL2 family members has been associated with the protection against the development of different autoimmune diseases. However, multiple mechanisms were proposed to be responsible for such protective effect. The purpose of this study was to explore the effect of the Tcell overexpression of BCL2A1, an anti-apoptotic BCL2 family member without an effect on cell cycle progression, in the development of collagen-induced arthritis. Our results demonstrated an attenuated development of arthritis in these transgenic mice. The protective effect was unrelated to the suppressive activity of regulatory T cells but it was associated with a defective activation of p38 mitogen-activated protein kinase in CD4+ cells after in vitro TCR stimulation. In addition, the in vitro and in vivo TH17 differentiation were impaired in BCL2A1 transgenic mice. Taken together, we demonstrated here a previously unknown role for BCL2A1 controlling the activation of CD4+ cells and their differentiation into pathogenic proinflammatory TH17 cells and identified BCL2A1 as a potential target in the control of autoimmune/inflammatory diseases

Tracking CNS and systemic sources of oxidative stress during the course of chronic neuroinflammation

The functional dynamics and cellular sources of oxidative stress are central to understanding MS pathogenesis but remain elusive, due to the lack of appropriate detection methods. Here we employ NAD(P)H fluorescence lifetime imaging to detect functional NADPH oxidases (NOX enzymes) in vivo to identify inflammatory monocytes, activated microglia, and astrocytes expressing NOX1 as major cellular sources of oxidative stress in the central nervous system of mice affected by experimental autoimmune encephalomyelitis (EAE). This directly affects neuronal function in vivo, indicated by sustained elevated neuronal calcium. The systemic involvement of oxidative stress is mirrored by overactivation of NOX enzymes in peripheral CD11b(+) cells in later phases of both MS and EAE. This effect is antagonized by systemic intake of the NOX inhibitor and anti-oxidant epigallocatechin-3-gallate. Together, this persistent hyper-activation of oxidative enzymes suggests an "oxidative stress memory" both in the periphery and CNS compartments, in chronic neuroinflammation

Eros is a novel transmembrane protein that controls the phagocyte respiratory burst and is essential for innate immunity

The phagocyte respiratory burst is crucial for innate immunity. The transfer of electrons to oxygen is mediated by a membrane-bound heterodimer, comprising gp91$\textit{phox}$ and p22$\textit{phox}$ subunits. Deficiency of either subunit leads to severe immunodeficiency. We describe Eros (essential for reactive oxygen species), a protein encoded by the previously undefined mouse gene $\textit{bc017643}$, and show that it is essential for host defense via the phagocyte NAPDH oxidase. Eros is required for expression of the NADPH oxidase components, gp91$\textit{phox}$ and p22$\textit{phox}$. Consequently, $\textit{Eros}$-deficient mice quickly succumb to infection. $\textit{Eros}$ also contributes to the formation of neutrophil extracellular traps (NETS) and impacts on the immune response to melanoma metastases. $\textit{Eros}$ is an ortholog of the plant protein Ycf4, which is necessary for expression of proteins of the photosynthetic photosystem 1 complex, itself also an NADPH oxio-reductase. We thus describe the key role of the previously uncharacterized protein Eros in host defense.D.C. Thomas was funded by a Wellcome Trust/CIMR Next Generation Fellowship, a National Institute for Health Research (NIHR) Clinical Lectureship, and a Starter Grant for Clinical Lecturers (Academy of Medical Sciences). K.G.C. Smith was funded by funded by the Medical Research Council (program grant MR/L019027) and is a Wellcome Investigator and a NIHR Senior Investigator. S. Clare and G. Dougan were funded by the Wellcome Trust (grant 098051). The Cambridge Institute for Medical Research is in receipt of a Wellcome Trust Strategic Award (079895). J.C.L is funded by a Wellcome Intermediate Clinical Fellowship 105920/2/14/2

Von Willebrand Factor Gene Variants Associate with Herpes simplex Encephalitis

Herpes simplex encephalitis (HSE) is a rare complication of Herpes simplex virus type-1 infection. It results in severe parenchymal damage in the brain. Although viral latency in neurons is very common in the population, it remains unclear why certain individuals develop HSE. Here we explore potential host genetic variants predisposing to HSE. In order to investigate this we used a rat HSE model comparing the HSE susceptible SHR (Spontaneously Hypertensive Rats) with the asymptomatic infection of BN (Brown Norway). Notably, both strains have HSV-1 spread to the CNS at four days after infection. A genome wide linkage analysis of 29 infected HXB/BXH RILs (recombinant inbred lines-generated from the prior two strains), displayed variable susceptibility to HSE enabling the definition of a significant QTL (quantitative trait locus) named Hse6 towards the end of chromosome 4 (160.89-174Mb) containing the Vwf (von Willebrand factor) gene. This was the only gene in the QTL with both cis-regulation in the brain and included several non-synonymous SNPs (single nucleotide polymorphism). Intriguingly, in human chromosome 12 several SNPs within the intronic region between exon 43 and 44 of the VWF gene were associated with human HSE pathogenesis. In particular, rs917859 is nominally associated with an odds ratio of 1.5 (95% CI 1.11-2.02; p-value = 0.008) after genotyping in 115 HSE cases and 428 controls. Although there are possibly several genetic and environmental factors involved in development of HSE, our study identifies variants of the VWF gene as candidates for susceptibility in experimental and human HSE