Detection of cardiac myosin heavy chain-α-specific CD4 cells by using MHC class II/IAk tetramers in A/J mice

Preclinical mouse models of immune checkpoint inhibitor-associated myocarditis

In this Review, we present a comprehensive analysis of preclinical models used to study immune checkpoint inhibitor-associated myocarditis (hereafter ICI-myocarditis), a potentially lethal immune-related adverse event. We begin by providing an overview of immune checkpoint inhibitors, highlighting how their efficacy in cancer treatment is counterbalanced by their predisposition to cause immune-related adverse events. Next, we draw from human data to identify disease features that an effective mouse model should ideally mimic. After that, we present a critical evaluation of a wide variety of existing mouse models including genetic, pharmacological and humanized models. We summarize insights gathered about the underlying mechanisms of ICI-myocarditis and the role of mouse models in these discoveries. We conclude with a perspective on the future of preclinical models, highlighting potential model improvements and research directions that could strengthen our understanding of ICI-myocarditis, ultimately improving patient outcomes.

Investigation into Cardiac Myhc-α 334-352-Specific TCR Transgenic Mice Reveals a Role for Cytotoxic CD4 T Cells in the Development of Cardiac Autoimmunity

Myocarditis is one of the major causes of heart failure in children and young adults and can lead to dilated cardiomyopathy. Lymphocytic myocarditis could result from autoreactive CD4+ and CD8+ T cells, but defining antigen specificity in disease pathogenesis is challenging. To address this issue, we generated T cell receptor (TCR) transgenic (Tg) C57BL/6J mice specific to cardiac myosin heavy chain (Myhc)-α 334-352 and found that Myhc-α-specific TCRs were expressed in both CD4+ and CD8+ T cells. To investigate if the phenotype is more pronounced in a myocarditis-susceptible genetic background, we backcrossed with A/J mice. At the fourth generation of backcrossing, we observed that Tg T cells from naïve mice responded to Myhc-α 334-352, as evaluated by proliferation assay and carboxyfluorescein succinimidyl ester staining. The T cell responses included significant production of mainly pro-inflammatory cytokines, namely interferon (IFN)-γ, interleukin-17, and granulocyte macrophage-colony stimulating factor. While the naïve Tg mice had isolated myocardial lesions, immunization with Myhc-α 334-352 led to mild myocarditis, suggesting that further backcrossing to increase the percentage of A/J genome close to 99.99% might show a more severe disease phenotype. Further investigations led us to note that CD4+ T cells displayed the phenotype of cytotoxic T cells (CTLs) akin to those of conventional CD8+ CTLs, as determined by the expression of CD107a, IFN-γ, granzyme B natural killer cell receptor (NKG)2A, NKG2D, cytotoxic and regulatory T cell molecules, and eomesodermin. Taken together, the transgenic system described in this report may be a helpful tool to distinguish the roles of cytotoxic cardiac antigen-specific CD4+ T cells vs. those of CD8+ T cells in the pathogenesis of myocarditis.

Transgenic Mice Expressing Functional TCRs Specific to Cardiac Myhc-α 334-352 on Both CD4 and CD8 T Cells Are Resistant to the Development of Myocarditis on C57BL/6 Genetic Background

Myocarditis is a predominant cause of congestive heart failure and sudden death in children and young adolescents that can lead to dilated cardiomyopathy. Lymphocytic myocarditis mediated by T cells can result from the recognition of cardiac antigens that may involve CD4 or CD8 T cells or both. In this report, we describe the generation of T cell receptor (TCR) transgenic mice on a C57BL/6 genetic background specific to cardiac myosin heavy chain (Myhc)-α 334-352 and make the following observations: First, we verified that Myhc-α 334-352 was immunogenic in wild-type C57BL/6 mice and induced antigen-specific CD4 T cell responses despite being a poor binder of IAb; however, the immunized animals developed only mild myocarditis. Second, TCRs specific to Myhc-α 334-352 in transgenic mice were expressed in both CD4 and CD8 T cells, suggesting that the expression of epitope-specific TCR is common to both cell types. Third, although T cells from naïve transgenic mice did not respond to Myhc-α 334-352, both CD4 and CD8 T cells from animals immunized with Myhc-α 334-352 responded to the peptide, indicating that antigen priming is necessary to break tolerance. Fourth, although the transgenic T cells could produce significant amounts of interferon-γ and interleukin-17, the immunized animals developed only mild disease, indicating that other soluble factors might be necessary for developing severe myocarditis. Alternatively, the C57BL/6 genetic background might be a major contributing factor for resistance to the development of myocarditis. Taken together, our model permits the determination of the roles of both CD4 and CD8 T cells to understand the disease-resistance mechanisms of myocarditis in a single transgenic system antigen-specifically.

Mt10-CVB3 Vaccine Virus Protects against CVB4 Infection by Inducing Cross-Reactive, Antigen-Specific Immune Responses

Group B coxsackieviruses (CVB) containing six serotypes, B1–B6, affect various organs, and multiple serotypes can induce similar diseases such as myocarditis and pancreatitis. Yet, no vaccines are currently available to prevent these infections. Translationally, the derivation of vaccines that offer protection against multiple serotypes is highly desired. In that direction, we recently reported the generation of an attenuated strain of CVB3, termed Mt10, which completely protects against both myocarditis and pancreatitis induced by the homologous wild-type CVB3 strain. Here, we report that the Mt10 vaccine can induce cross-protection against multiple CVB serotypes as demonstrated with CVB4. We note that the Mt10 vaccine could induce cross-reactive neutralizing antibodies (nABs) against both CVB1 and CVB4. In challenge studies with CVB4, the efficacy of the Mt10 vaccine was found to be 92%, as determined by histological evaluation of the heart and pancreas. Antibody responses induced in Mt10/CVB4 challenged animals indicated the persistence of cross-reactive nABs against CVB1, CVB3, and CVB4. Evaluation of antigen-specific immune responses revealed viral protein 1 (VP1)-reactive antibodies, predominantly IgG2a, IgG2b, IgG3, and IgG1. Similarly, by using major histocompatibility complex class II tetramers, we noted induction of VP1-specific CD4 T cells capable of producing multiple T cell cytokines, with interferon-γ being predominant. Finally, none of the vaccine recipients challenged with CVB4 revealed the presence of viral nucleic acid in the heart or pancreas. Taken together, our data suggest that the Mt10 vaccine can prevent infections caused by multiple CVB serotypes, paving the way for the development of monovalent CVB vaccines to prevent heart and pancreatic diseases of enteroviral origin.

Attenuated strain of CVB3 with a mutation in the CAR-interacting region protects against both myocarditis and pancreatitis

Coxsackievirus B3 (CVB3), is commonly implicated in myocarditis, which can lead to dilated cardiomyopathy, in addition to causing acute pancreatitis and meningitis. Yet, no vaccines are currently available to prevent this infection. Here, we describe the derivation of a live attenuated vaccine virus, termed mutant (Mt) 10, encoding a single amino acid substitution H790A within the viral protein 1, that prevents CVB3 infection in mice and protects from both myocarditis and pancreatitis in challenge studies. We noted that animals vaccinated with Mt 10 developed virus-neutralizing antibodies, predominantly containing IgG2a and IgG2b, and to a lesser extent IgG3 and IgG1. Furthermore, by using major histocompatibility complex class II dextramers and tetramers, we demonstrated that Mt 10 induces antigen-specific T cell responses that preferentially produce interferon-γ. Finally, neither vaccine recipients nor those challenged with the wild-type virus revealed evidence of autoimmunity or cardiac injury as determined by T cell response to cardiac myosin and measurement of circulating cardiac troponin I levels, respectively. Together, our data suggest that Mt 10 is a vaccine candidate that prevents CVB3 infection through the induction of neutralizing antibodies and antigen-specific T cell responses, the two critical components needed for complete protection against virus infections in vaccine studies.

Viral myocarditis involves the generation of autoreactive T cells with multiple antigen specificities that localize in lymphoid and non-lymphoid organs in the mouse model of CVB3 infection

Autoreactive T cells may contribute to post-viral myocarditis induced with Coxsackievirus B3 (CVB3), but the underlying mechanisms of their generation are unclear. Here, we have comprehensively analyzed the generation of antigen-specific, autoreactive T cells in the mouse model of CVB3 infection for antigens implicated in patients with myocarditis/dilated cardiomyopathy. First, comparative analysis of CVB3 proteome with five autoantigens led us to identify three mimicry epitopes, one each from adenine nucleotide translocator 1 (ANT), sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) and cardiac troponin I. None of these induced cross-reactive T cell responses. Next, we generated major histocompatibility complex (MHC) class II dextramers to enumerate the frequencies of antigen-specific T cells to determine whether T cells with multiple antigen specificities are generated by CVB3 infection. These analyses revealed appearance of CD4 T cells positive for SERCA2a 971-990, and cardiac myosin heavy chain-α (Myhc) 334-352 dextramers, both in the periphery and also in the hearts of CVB3-infected animals. While ANT 21-40 dextramer⁺ T cells were inconsistently detected, the β1-adrenergic receptor 181-200/211-230 or branched chain α-ketoacid dehydrogenase kinase 111-130 dextramer⁺ cells were absent. Interestingly, SERCA2a 971-990, Myhc 334-352 and ANT 21-40 dextramer⁺ cells were also detected in the liver indicating that they may have a pathogenic role. Finally, we demonstrate that the SERCA2a 971-990-reactive T cells generated in CVB3 infection could transfer disease to naïve mice. The data suggest that CVB3 infection can lead to the generation of autoreactive T cells for multiple antigens indicating a possibility that the autoreactive T cells localized in the liver can potentially circulate and contribute to the development of viral myocarditis.

Identification of Immunogenic Epitopes That Permit the Detection of Antigen-Specific T Cell Responses in Multiple Serotypes of Group B Coxsackievirus Infections

Coxsackievirus group B (CVB) contains six serotypes that can affect various organs. Some of these organ-specific diseases such as myocarditis and pancreatitis can be caused by more than one serotype. Thus, development of immunological tools common to multiple serotypes is desired. This is especially critical for analyzing antigen-specific T cell responses at a single cell level. To this end, we made efforts to identify the immunogenic epitopes of CVB3 leading us to localize three T cell epitopes within the viral protein 1 (VP1) namely, VP1 681-700, VP1 721-740 and VP1 771-790. First, we confirmed their immunogenicity in the immunization settings. Second, we sought to verify the ability of VP1 epitopes to bind major histocompatibility complex (MHC) class II (IA^k) molecules. Third, we created MHC class II (IA^k) dextramers and tetramers and ascertained the T cell responses to be antigen-specific. Fourth, we analyzed the T cell responses in animals infected with CVB3 and noted the magnitude of antigen-specific T cell responses occurring in the order of VP1 721-740 and VP1 681-700 followed by VP1 771-790 as verified by proliferation assay and IA^k tetramer staining. All epitopes induced interferon (IFN)-γ as a major cytokine. Finally, we investigated whether the VP1 tools generated for CVB3 can also be used to verify T cell responses in infections caused by other serotypes. To this end, we established the CVB4 infection model in A/J mice and found that the CVB4 infection led to the induction of IFN-γ-producing T cell responses primarily for VP1 721-740 and VP1 681-700. Thus, the VP1-specific tools, particularly IA^k tetramers can be used to monitor anti-viral T cell responses in multiple CVB serotypes.

An evidence for surface expression of an immunogenic epitope of sarcoplasmic/endoplasmic reticulum calcium-ATPase2a on antigen-presenting cells from naive mice in the mediation of autoimmune myocarditis

We recently reported identification of sarcoplasmic/endoplasmic reticulum calcium-ATPase2a (SERCA2a) 971-990, which induces atrial myocarditis by generating autoreactive T cells in A/J mice. However, it was unknown how antigen-sensitized T cells could recognize SERCA2a 971-990, since SERCA2a-expression is confined to an intracellular compartment. In this report, we present evidence that antigen-presenting cells (APCs) from lymphoid and non-lymphoid organs in naïve animals present SERCA2a 971-990 and stimulate antigen-specific T cells. Using major histocompatibility complex (MHC) class II dextramers for SERCA2a 971-990, we created a panel of T cell hybridomas and demonstrated that splenocytes from naïve A/J mice stimulated the hybridoma cells without exogenous supplementation of SERCA2a 971-990. We then recapitulated this phenomenon by using SERCA2a 971-990 -specific primary T cells, verifying that the T cell responses were MHC-restricted. Furthermore, SERCA2a 971-990 -sensitzed T cells exposed to APCs from naïve mice were found to produce the inflammatory cytokines interferon-γ, granulocyte macrophage colony stimulating factor, and interleukin-17A, which are implicated in the induction of myocarditis. Finally, while T cells exposed to mononuclear cells (MNCs) obtained from heart and liver also responded similarly to splenocytes, endothelial cells (ECs) generated from the corresponding organs displayed opposing effects, in that the proliferative responses were suppressed with the heart ECs, but not with the liver ECs. Taken together, our data suggest that the surface expression of SERCA2a 971-990 by naïve APCs can potentially trigger pathogenic autoreactive T cell responses under conditions of autoimmunity, which may have implications in endothelial dysfunction.

High-throughput identification of human antigen-specific CD8+ and CD4+ T cells using soluble pMHC multimers

Peptide major histocompatibility complex (pMHC) multimers have been used since decades to identify, isolate and analyze antigen-specific T cells by flow (and more recently mass) cytometry. Yet well established as a standard technology, improvements are still required to face the growing needs of personalized immune monitoring. Here we review the latest developments about (i) the quality of pMHC class I and II monomers, (ii) the importance of the multimeric scaffold, (iii) the staining conditions and (iv) the high-throughput synthesis of pMHC monomers. Finally, innovative multiplexed, combinatorial strategies for parallel detection of antigen-specific T cells in a single sample are discussed.

Epitope Mapping of SERCA2a Identifies an Antigenic Determinant That Induces Mainly Atrial Myocarditis in A/J Mice

Sarcoplasmic/endoplasmic reticulum Ca2+ adenosine triphosphatase (SERCA)2a, a critical regulator of calcium homeostasis, is known to be decreased in heart failure. Patients with myocarditis or dilated cardiomyopathy develop autoantibodies to SERCA2a suggesting that they may have pathogenetic significance. In this report, we describe epitope mapping analysis of SERCA2a in A/J mice that leads us to make five observations: 1) SERCA2a contains multiple T cell epitopes that induce varying degrees of myocarditis. One epitope, SERCA2a 971-990, induces widespread atrial inflammation without affecting noncardiac tissues; the cardiac abnormalities could be noninvasively captured by echocardiography, electrocardiography, and magnetic resonance microscopy imaging. 2) SERCA2a 971-990-induced disease was associated with the induction of CD4 T cell responses and the epitope preferentially binds MHC class II/IAk rather than IEk By creating IAk/and IEk/SERCA2a 971-990 dextramers, the T cell responses were determined by flow cytometry to be Ag specific. 3) SERCA2a 971-990-sensitized T cells produce both Th1 and Th17 cytokines. 4) Animals immunized with SERCA2a 971-990 showed Ag-specific Abs with enhanced production of IgG2a and IgG2b isotypes, suggesting that SERCA2a 971-990 can potentially act as a common epitope for both T cells and B cells. 5) Finally, SERCA2a 971-990-sensitized T cells were able to transfer disease to naive recipients. Together, these data indicate that SERCA2a is a critical autoantigen in the mediation of atrial inflammation in mice and that our model may be helpful to study the inflammatory events that underlie the development of conditions such as atrial fibrillation in humans.

β1-Adrenergic Receptor Contains Multiple IAk and IEk Binding Epitopes That Induce T Cell Responses with Varying Degrees of Autoimmune Myocarditis in A/J Mice

Myocarditis/dilated cardiomyopathy (DCM) patients can develop autoantibodies to various cardiac antigens and one major antigen is β1-adrenergic receptor (β₁AR). Previous reports indicate that animals immunized with a β₁AR fragment encompassing, 197–222 amino acids for a prolonged period can develop DCM by producing autoantibodies, but existence of T cell epitopes, if any, were unknown. Using A/J mice that are highly susceptible to lymphocytic myocarditis, we have identified β₁AR 171–190, β₁AR 181–200, and β₁AR 211–230 as the major T cell epitopes that bind major histocompatibility complex class II/IA^k or IE^k alleles, and by creating IA^k and IE^k dextramers, we demonstrate that the CD4 T cell responses to be antigen-specific. Of note, all the three epitopes were found also to stimulate CD8 T cells suggesting that they can act as common epitopes for both CD4 and CD8 T cells. While, all epitopes induced only mild myocarditis, the disease-incidence was enhanced in animals immunized with all the three peptides together as a cocktail. Although, antigen-sensitized T cells produced mainly interleukin-17A, their transfer into naive animals yielded no disease. But, steering for T helper 1 response led the T cells reacting to one epitope, β₁AR 181–200 to induce severe myocarditis in naive mice. Finally, we demonstrate that all three β₁AR epitopes to be unique for T cells as none of them induced antibody responses. Conversely, animals immunized with a non-T cell activator, β₁AR 201–220, an equivalent of β₁AR 197–222, had antibodies comprising of all IgG isotypes and IgM except, IgA and IgE. Thus, identification of T cell and B cell epitopes of β₁AR may be helpful to determine β₁AR-reactive autoimmune responses in various experimental settings in A/J mice.

Major Histocompatibility Complex Class II Dextramers: New Tools for the Detection of antigen-Specific, CD4 T Cells in Basic and Clinical Research

The advent of major histocompatibility complex (MHC) tetramer technology has been a major contribution to T cell immunology, because tetramer reagents permit detection of antigen-specific T cells at the single-cell level in heterogeneous populations by flow cytometry. However, unlike MHC class I tetramers, the utility of MHC class II tetramers has been less frequently reported. MHC class II tetramers can be used successfully to enumerate the frequencies of antigen-specific CD4 T cells in cells activated in vitro, but their use for ex vivo analyses continues to be a problem, due in part to their activation dependency for binding with T cells. To circumvent this problem, we recently reported the creation of a new generation of reagents called MHC class II dextramers, which were found to be superior to their counterparts. In this review, we discuss the utility of class II dextramers vis-a-vis tetramers, with respect to their specificity and sensitivity, including potential applications and limitations.

Versatility of using major histocompatibility complex class II dextramers for derivation and characterization of antigen-specific, autoreactive T cell hybridomas

Antigen-specific, T cell hybridomas are useful to study the cellular, molecular and functional events, but their generation is a lengthy process. Thus, there is a need to develop robust methods to generate the hybridoma clones rapidly in a short period of time. To this end, we have demonstrated a novel approach using major histocompatibility complex (MHC) class II dextramers to generate T cell hybridomas for an autoantigen, proteolipid protein (PLP) 139-151. Using MHC class II dextramers assembled with PLP 139-151 as screening and sorting tools, we successfully obtained mono antigen-specific clones within seven to eight weeks. In conjunction with other T cell markers, dextramers permitted phenotypic characterization of hybridoma clones for their antigen specificity in a single step by flow cytometry. Importantly, we achieved successful fusions using dextramer(+) cells sorted by flow cytometry as a starting population, resulting in direct identification of multiple antigen-specific clones. Characterization of selected clones led us to identify chemokine receptor, CCR4(+) to be expressed consistently, but their cytokine-producing ability was variable. Our work provides a proof-of principle that the antigen-specific, CD4 T cell hybridoma clones can be generated directly using MHC class II dextramers. The availability of hybridoma clones that bind dextramers may serve as useful tools for various in vitro and in vivo applications.

Localization of CD8 T cell epitope within cardiac myosin heavy chain-α334-352 that induces autoimmune myocarditis in A/J mice

BACKGROUND

Cardiac myosin heavy chain-α (Myhc), an intracellular protein expressed in the cardiomyocytes, has been identified as a major autoantigen in cardiac autoimmunity. In our studies with Myhc334-352-induced experimental autoimmune myocarditis in A/J mice (H-2a), we discovered that Myhc334-352, supposedly a CD4 T cell epitope, also induced antigen-specific CD8 T cells that transfer disease to naive animals.

METHODS AND RESULTS

In our efforts to identify the CD8 T cell determinants, we localized Myhc338-348 within the full length-Myhc334-352, leading to four key findings. (1) By acting as a dual epitope, Myhc338-348 induces both CD4 and CD8 T cell responses. (2) In a major histocompatibility complex (MHC) class I-stabilization assay, Myhc338-348 was found to bind H-2Dd-but not H-2Kk or H-2Ld-alleles. (3) The CD8 T cell response induced by Myhc338-348 was antigen-specific, as evaluated by MHC class I/H-2Dd dextramer staining. The antigen-sensitized T cells predominantly produced interferon-γ, the critical cytokine of effector cytotoxic T lymphocytes. (4) Myhc338-348 was found to induce myocarditis in immunized animals as determined by histology and magnetic resonance microscopy imaging.

CONCLUSIONS

Our data provide new insights as to how different immune cells can recognize the same antigen and inflict damage through different mechanisms.

Direct staining with major histocompatibility complex class II dextramers permits detection of antigen-specific, autoreactive CD4 T cells in situ

We report here the utility of major histocompatibility complex (MHC) class II dextramers for in situ detection of self-reactive CD4 T cells in two target organs, the brain and heart. We optimized the conditions for in situ detection of antigen-specific CD4 T cells using brain sections obtained from SJL mice immunized with myelin proteolipid protein (PLP) 139–151; the sections were costained with IA^s/PLP 139–151 (specific) or Theiler's murine encephalomyelitis virus (TMEV) 70–86 (control) dextramers and anti-CD4. Analysis of sections by laser scanning confocal microscope revealed detection of cells positive for PLP 139–151 but not for TMEV 70–86 dextramers to be colocalized with CD4-expressing T cells, indicating that the staining was specific to PLP 139–151 dextramers. Further, we devised a method to reliably enumerate the frequencies of antigen-specific T cells by counting the number of dextramer⁺ CD4⁺ T cells in the ‘Z’ serial images acquired sequentially. We next extended these observations to detect cardiac myosin-specific T cells in autoimmune myocarditis induced in A/J mice by immunizing with cardiac myosin heavy chain-α (Myhc) 334–352. Heart sections prepared from immunized mice were costained with Myhc 334–352 (specific) or bovine ribonuclease 43–56 (control) dextramers together with anti-CD4; the sections showed the infiltrations of Myhc-specific CD4 T cells. The data suggest that MHC class II dextramers are useful tools for enumerating the frequencies of antigen-specific CD4 T cells in situ by direct staining without having to amplify the fluorescent signals, an approach commonly employed with conventional MHC tetramers.

Mimicry epitope from Ehrlichia canis for interphotoreceptor retinoid-binding protein 201-216 prevents autoimmune uveoretinitis by acting as altered peptide ligand

We report here identification of novel mimicry epitopes for interphotoreceptor retinoid-binding protein (IRBP) 201-216, a candidate ocular antigen that causes experimental autoimmune uveoretinitis (EAU) in A/J mice. One mimicry epitope from Ehrlichia canis (EHC), designated EHC 44-59, induced cross-reactive T cells for IRBP 201-216 capable of producing T helper (Th)1 and Th17 cytokines, but failed to induce EAU in A/J mice. In addition, animals first primed with suboptimal doses of IRBP 201-216 and subsequently immunized with EHC 44-59 did not develop EAU; rather, the mimicry epitope prevented the disease induced by IRBP 201-216. However, alteration in the composition of EHC 44-59 by substituting alanine with valine at position 49, similar to the composition of IRBP 201-216, enabled the mimicry epitope to acquire uveitogenicity. The data provide new insights as to how microbes containing mimicry sequences for retinal antigens can prevent ocular inflammation by acting as naturally occurring altered peptide ligands.

Analysis, Isolation, and Activation of Antigen-Specific CD4(+) and CD8(+) T Cells by Soluble MHC-Peptide Complexes

T cells constitute the core of adaptive cellular immunity and protect higher organisms against pathogen infections and cancer. Monitoring of disease progression as well as prophylactic or therapeutic vaccines and immunotherapies call for conclusive detection, analysis, and sorting of antigen-specific T cells. This is possible by means of soluble recombinant ligands for T cells, i.e., MHC class I-peptide (pMHC I) complexes for CD8(+) T cells and MHC class II-peptide (pMHC II) complexes for CD4(+) T cells and flow cytometry. Here we review major developments in the development of pMHC staining reagents and their diverse applications and discuss perspectives of their use for basic and clinical investigations.

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.

Immunological variation between inbred laboratory mouse strains: points to consider in phenotyping genetically immunomodified mice

Inbred laboratory mouse strains are highly divergent in their immune response patterns as a result of genetic mutations and polymorphisms. The generation of genetically engineered mice (GEM) has, in the past, used embryonic stem (ES) cells for gene targeting from various 129 substrains followed by backcrossing into more fecund mouse strains. Although common inbred mice are considered "immune competent," many have variations in their immune system-some of which have been described-that may affect the phenotype. Recognition of these immune variations among commonly used inbred mouse strains is essential for the accurate interpretation of expected phenotypes or those that may arise unexpectedly. In GEM developed to study specific components of the immune system, accurate evaluation of immune responses must take into consideration not only the gene of interest but also how the background strain and microbial milieu contribute to the manifestation of findings in these mice. This article discusses points to consider regarding immunological differences between the common inbred laboratory mouse strains, particularly in their use as background strains in GEM.

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

BACKGROUND

Tetramers 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.

RESULTS

The 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.

CONCLUSIONS

The data suggest that MHC dextramers are useful tools to track the generation and functionalities of self-reactive CD4 cells in various experimental systems.