Jay Reddy

Cutting edge: CD4+CD25+ regulatory T cells contribute to gender differences in susceptibility to experimental autoimmune encephalomyelitis

Female B10.S mice are highly resistant to proteolipid protein (PLP) 139–151-induced experimental autoimmune encephalomyelitis (EAE) and depletion of PLP 139–151-reactive CD4+CD25+ regulatory T (Treg) cells can slightly increase their EAE susceptibility. Although male B10.S mice are moderately susceptible to EAE, we report that depletion of Treg cells in male B10.S mice before immunization with PLP 139–151 renders them highly susceptible to severe EAE with more CNS neutrophil infiltrates than nondepleted controls. Increased susceptibility is associated with an enhanced PLP 139–151-specific T cell response and greater production of IFN-γ, IL-6, and IL-17. Male CD4+CD25− effector cells depleted of Treg cells proliferate to a greater degree than those from females in response to either anti-CD3 or PLP 139–151. These data suggest that because of their capacity to regulate potent autoaggressive effector cells, Treg cells partly contribute to the resistance to autoimmunity in the male mice.

miR-27b*, an oxidative stress-responsive microRNA modulates nuclear factor-kB pathway in RAW 264.7 cells

Reactive oxygen species (ROS) produced in macrophages is critical for microbial killing, but they also take part in inflammation and antigen presentation functions. MicroRNAs (miRNAs) are endogenous regulators of gene expression, and they can control immune responses. To dissect the complex nature of ROS-mediated effects in macrophages, we sought to characterize miRNAs that are responsive to oxidative stress-induced with hydrogen peroxide (H2O2) in the mouse macrophage cell line, RAW 264.7. We have identified a set of unique miRNAs that are differentially expressed in response to H2O2. These include miR-27a*, miR-27b*, miR-29b*, miR-24-2*, and miR-21*, all of which were downregulated except for miR-21*. By using luciferase reporter vector containing nuclear factor-kB (NF-kB) response elements, we demonstrate that overexpression of miR-27b* suppresses lipopolysaccharide-induced activation of NF-kB in RAW 264.7 cells. Our data suggest that macrophage functions can be regulated by oxidative stress-responsive miRNAs by modulating the NF-kB pathway.

Distinct Functions of Autoreactive Memory and Effector CD4+ T Cells in Experimental Autoimmune Encephalomyelitis

The persistence of human autoimmune diseases is thought to be mediated predominantly by memory T cells. We investigated the phenotype and migration of memory versus effector T cells in vivo in experimental autoimmune encephalomyelitis (EAE). We found that memory CD4(+) T cells up-regulated the activation marker CD44 as well as CXCR3 and ICOS, proliferated more and produced more interferon-gamma and less interleukin-17 compared to effector T cells. Moreover, adoptive transfer of memory T cells into T cell receptor (TCR)alphabeta(-/-) recipients induced more severe disease than did effector CD4(+) T cells with marked central nervous system inflammation and axonal damage. The uniqueness of disease mediated by memory T cells was confirmed by the differential susceptibility to immunomodulatory therapies in vivo. CD28-B7 T cell costimulatory signal blockade by CTLA4Ig suppressed effector cell-mediated EAE but had minimal effects on disease induced by memory cells. In contrast, ICOS-B7h blockade exacerbated effector T cell-induced EAE but protected from disease induced by memory T cells. However, blockade of the OX40 (CD134) costimulatory pathway ameliorated disease mediated by both memory and effector T cells. Our data extend the understanding of the pathogenicity of autoreactive memory T cells and have important implications for the development of novel therapies for human autoimmune diseases.

Identification of novel mimicry epitopes for cardiac myosin heavy chain-α that induce autoimmune myocarditis in A/J mice.

Myocarditis is one cause of sudden cardiac death in young adolescents, and individuals affected with myocarditis can develop dilated cardiomyopathy, a frequent reason for heart transplantation. Exposure to environmental microbes has been suspected in the initiation of heart autoimmunity, but the direct causal link is lacking. We report here identification of novel mimicry epitopes that bear sequences similar to those in cardiac myosin heavy chain (MYHC)-α 334-352. These epitopes represent Bacillus spp., Magnetospirillum gryphiswaldense, Cryptococcus neoformans and Zea mays. The mimicry peptides induced varying degrees of myocarditis in A/J mice reminiscent of the disease induced with MYHC-α 334-352. We demonstrate that the mimics induce cross-reactive T cell responses for MYHC-α 334-352 as verified by MHC class II IA(k)/tetramer staining and Th-1 and Th-17 cytokines similar to those of MYHC-α 334-352. The data suggest that exposure to environmental microbes which are otherwise innocuous can predispose to heart autoimmunity by molecular mimicry.

Coxsackievirus B3 infection leads to the generation of cardiac myosin heavy chain-α-reactive CD4 T cells in A/J mice.

Enteroviruses like coxsackievirus B3 (CVB3) are common suspects in myocarditis/dilated cardiomyopathy patients. Autoimmunity has been proposed as an underlying mechanism, but direct evidence of its role is lacking. To delineate autoimmune response in CVB3 myocarditis, we used IA(k) dextramers for cardiac myosin heavy chain (Myhc)-α 334-352. We have demonstrated that myocarditis-susceptible A/J mice infected with CVB3 generate Myhc-α-reactive CD4 T cells and such a repertoire was absent in naïve mice as measured by proliferative response to Myhc-α 334-352 and IA(k) dextramer staining. We also detected Myhc-α 334-352 dextramer(+) cells in the hearts of CVB3-infected mice. The autoreactive T cell repertoire derived from infected mice contained a high frequency of interleukin-17-producing cells capable of inducing myocarditis in naïve recipients. The data suggest that CVB3, a bona fide pathogen of cardiovascular system that primarily infects the heart can lead to the secondary generation of autoreactive T cells and contribute to cardiac pathology.

Detection of autoreactive CD4 T cells using major histocompatibility complex class II dextramers

BackgroundTetramers are useful tools to enumerate the frequencies of antigen-specific T cells. However, unlike CD8 T cells, CD4 T cells - especially self-reactive cells - are challenging to detect with major histocompatibility complex (MHC) class II tetramers because of low frequencies and low affinities of their T cell receptors to MHC-peptide complexes. Here, we report the use of fluorescent multimers, designated MHC dextramers that contain a large number of peptide-MHC complexes per reagent.ResultsThe utility of MHC dextramers was evaluated in three autoimmune disease models: 1) proteolipid protein (PLP) 139-151-induced experimental autoimmune encephalomyelitis in SJL/J (H-2s) mice; 2) myelin oligodendrocyte glycoprotein (MOG) 35-55-induced experimental autoimmune encephalomyelitis in C57Bl/6 (H-2b) mice; and 3) cardiac myosin heavy chain (Myhc)-α 334-352-induced experimental autoimmune myocarditis in A/J (H-2a) mice. Flow cytometrically, we demonstrate that IAs/PLP 139-151, IAb/MOG 35-55 and IAk/Myhc-α 334-352 dextramers detect the antigen-sensitized cells with specificity, and with a detection sensitivity significantly higher than that achieved with conventional tetramers. Furthermore, we show that binding of dextramers, but not tetramers, is less dependent on the activation status of cells, permitting enumeration of antigen-specific cells ex vivo.ConclusionsThe data suggest that MHC dextramers are useful tools to track the generation and functionalities of self-reactive CD4 cells in various experimental systems.

An epitope from Acanthamoeba castellanii that cross-react with proteolipid protein 139-151-reactive T cells induces autoimmune encephalomyelitis in SJL mice

We report here that an epitope (aa, 83-95) derived from Acanthamoeba castellanii (ACA) induces clinical signs of experimental autoimmune encephalomyelitis (EAE) in SJL/J mice reminiscent of the disease induced with myelin proteolipid protein (PLP) 139-151. By using IA(s)/tetramers, we demonstrate that both ACA 83-95 and PLP 139-151 generate antigen-specific cross-reactive CD4 T cells and the T cells secrete identical patterns of cytokines and induce EAE with a similar severity. These results may provide insights into the pathogenesis of multiple sclerosis and ACA-induced granulomatous encephalitis.

Autoimmunity in viral myocarditis

Purpose of reviewTo review how autoimmunity is induced in viral myocarditis. Recent findingsClinical and experimental myocarditis follows microbial infections, but autoimmunity to cardiac antigens leads to heart failure since infected myocytes are sparse and virus clearance is rapid. In mice, CD4+ T cells specific for cardiac alpha myosin heavy chain (&agr;MYHC) cause myocarditis and mice tolerized to &agr;MYHC are protected from virus challenge proving pathogenesis depends upon autoimmunity. Most importantly, multiple microbes share the same mimicking epitope with &agr;MYHC. Serial infections with very different microbes could result in memory responses to the shared epitope leading to aggressive and severe heart failure. A similar phenomenon may explain autoimmune diseases with suspected infectious causes, where specific pathogens have not been identified. Production of the relevant cardiac epitope for antigen presentation requires more than myosin release from dead myocytes. Otherwise, myocarditis would commonly follow myocardial infarcts. The inherent nature of the innate immune response associated with viral infections in the heart is crucial to cardiac epitope expression. SummaryAntigenic mimicry between microbes and cardiac proteins causes autoimmunity in myocarditis. Characteristics of innate immunity associated with cardiac infection determine relevant epitope expression (cryptic epitopes).

Gender differences in CNS autoimmunity induced by mimicry epitope for PLP 139-151 in SJL mice

Development of multiple sclerosis (MS) is more prevalent in females than in males, but the underlying mechanisms are not clear. Microbial infections have been suspected as triggers of MS and it is not known whether gender differences in reactivity to environmental antigens contribute to the disease pathogenesis. We demonstrated that ACA 83-95, a mimicry epitope from Acanthamoeba castellanii for proteolipid protein (PLP) 139-151, induces clinical signs of encephalomyelitis in both male and female SJL mice. Conversely ACA 83-95-induced effector cells from males fail to induce disease in female mice. Although we found no gender differences in the frequencies of antigen-specific cells including cytokine production, PLP-specific cells induced with ACA 83-95 differed in T cell receptor vβ usage from those induced with PLP 139-151. The data suggest that cross-reactive T cell expansion occurs similarly in both males and females, but their disease-inducing ability is influenced by gender.

Relevance of Molecular Mimicry in the Mediation of Infectious Myocarditis

Heart disease, the leading cause of death in humans, is estimated to affect one in four American adults in some form. One predominant cause of heart failure in young adults is myocarditis, which can lead to the development of dilated cardiomyopathy, a major indication for heart transplantation. Environmental microbes, including viruses, bacteria, and fungi that are otherwise innocuous, have the potential to induce inflammatory heart disease. As the list is growing, it is critical to determine the mechanisms by which microbes can trigger heart autoimmunity and, importantly, to identify their target antigens. This is especially true as microbes showing structural similarities with the cardiac antigens can predispose to heart autoimmunity by generating cross-reactive immune responses. In this review, we discuss the relevance of molecular mimicry in the mediation of infectious myocarditis.