Cytokine production by Vgamma(+)-T-cell subsets is an important factor determining CD4(+)-Th-cell phenotype and susceptibility of BALB/c mice to coxsackievirus B3-induced myocarditis

The Epidemiology of COVID-19 Vaccine-Induced Myocarditis

Background

In December 2019, the emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) led to the COVID-19 pandemic, with millions of deaths worldwide. Vaccine breakthroughs in late 2020 resulted in the authorization of COVID-19 vaccines. While these vaccines have demonstrated efficacy, evidence from vaccine safety monitoring systems around the globe supported a causal association between COVID-19 vaccines, in particular those using mRNA technology, i.e., Moderna's mRNA-1273 and Pfizer-BioNTech's BNT162b2, and myocarditis.

Objective

This paper aims to investigate the epidemiology of mRNA COVID-19 vaccine-induced myocarditis, including age, ethnicity, and gender associations with these vaccines. It also discusses the immunopathophysiological mechanisms of mRNA COVID-19 vaccine-associated myocarditis and outlines principles of diagnosis, clinical presentation, and management.

Methods

A literature review was conducted using PubMed, Embase, and Queen Mary University of London Library Services databases. Search terms included "myocarditis," "coronavirus disease 2019," "SARS-CoV-2," "mRNA Covid-19 vaccines," "Covid vaccine-associated myocarditis," "epidemiology," "potential mechanisms," "myocarditis diagnosis," and "myocarditis management."

Results

While the definite mechanism of mRNA COVID-19 vaccine-associated myocarditis remains ambiguous, potential mechanisms include molecular mimicry of spike proteins and activation of the adaptive immune response with dysregulated cytokine expression. Male predominance in COVID-19 vaccine-induced myocarditis may be attributed to sex hormones, variations in inflammatory reactions, coagulation states based on gender, and female-specific protective factors. Moreover, an analysis of diagnostic and management strategies reveals a lack of consensus on acute patient presentation management.

Conclusion

In contrast to viral infections that stand as the predominant etiological factor for myocarditis with more severe consequences, the mRNA COVID-19 vaccination elicits a mild and self-limiting manifestation of the condition. There is currently insufficient evidence to confirm the definite underlying mechanism of COVID-19 vaccine-associated myocarditis. Further research is needed to develop preventive and therapeutic solutions in this context.

Expression Profiles and Potential Functions of Long Non-Coding RNAs in the Heart of Mice With Coxsackie B3 Virus-Induced Myocarditis

Aims

Long non-coding RNAs (lncRNAs) are critical regulators of viral infection and inflammatory responses. However, the roles of lncRNAs in acute myocarditis (AM), especially fulminant myocarditis (FM), remain unclear.

Methods

FM and non-fulminant myocarditis (NFM) were induced by coxsackie B3 virus (CVB3) in different mouse strains. Then, the expression profiles of the lncRNAs in the heart tissues were detected by sequencing. Finally, the patterns were analyzed by Pearson/Spearman rank correlation, Kyoto Encyclopedia of Genes and Genomes, and Cytoscape 3.7.

Results

First, 1,216, 983, 1,606, and 2,459 differentially expressed lncRNAs were identified in CVB3-treated A/J, C57BL/6, BALB/c, and C3H mice with myocarditis, respectively. Among them, 88 lncRNAs were commonly dysregulated in all four models. Quantitative real-time polymerase chain reaction analyses further confirmed that four out of the top six commonly dysregulated lncRNAs were upregulated in all four models. Moreover, the levels of ENSMUST00000188819, ENSMUST00000199139, and ENSMUST00000222401 were significantly elevated in the heart and spleen and correlated with the severity of cardiac inflammatory infiltration. Meanwhile, 923 FM-specific dysregulated lncRNAs were detected, among which the levels of MSTRG.26098.49, MSTRG.31307.11, MSTRG.31357.2, and MSTRG.32881.28 were highly correlated with LVEF.

Conclusion

Expression of lncRNAs is significantly dysregulated in acute myocarditis, which may play different roles in the progression of AM.

T-cells in myocardial infarction: Culprit instigators or mere effectors?

Immune system activation and dysfunction characterize the early phase of reperfusion after a myocardial infarction (MI). Despite initially neglected, adaptive immunity has been recently showed to play an important role in this setting. In fact, the immune system can recognize sequestered antigens released by the necrotic tissue, initiating a deleterious autoimmune vicious circle leading to worse outcome. In their recent work, Angelini et al shed the light on a new feature of post-MI which involves two “old players” of post-ischemic myocardial injury: CD31 and matrix metalloproteinase (MMP)-9. Specifically, the authors showed that an enhancement of MMP-9 release could determine the cleavage of inhibitory CD31 from CD4+ T-cells surface in patients with Acute Coronary Syndromes (ACS). These findings open the room for new studies investigating the role of MMP9 in other pathological processes associated with a reduction of CD31 functionality, such as plaque instability and rupture. Of interest, in the case of a causative role for CD31 shedding in ACS would be confirmed, there might be a potential role for the administration of CD31 protein or analogue compounds to blunt post-ischemic cardiac inflammation and improve ACS outcome.

The adaptive immune response to cardiac injury-the true roadblock to effective regenerative therapies?

The regenerative capacity of adult human tissues and organs is limited, but recent developments have seen the advent of promising new technologies for regenerative therapy. The human heart is of particular interest for regenerative medicine, as cardiac tissue damage is repaired by the formation of rigid scar tissue, which causes inevitable structural changes and progressive functional decline leading to heart failure. Cardiac regenerative medicine aims to prevent scar formation or replace existing scars to halt or reverse adverse remodeling and therapeutic approaches include the use of biomaterials, gene therapies, delivery of growth factors, and (stem) cell therapies. Regenerative therapies, however, face significant obstacles in a hostile microenvironment. While the early immune response to a myocardial infarct is essential to ensure tissue integrity and to avoid fatal cardiac rupture, excessive activation of endogenous repair mechanisms may lead to ongoing inflammation, fibrosis, and sustained autoimmune-mediated tissue damage. Anti-cardiac autoreactivity of the adaptive immune system has been suggested to be involved in structural remodeling, functional decline, and the development of heart failure. It is, therefore, crucial to first understand the endogenous response to cardiac tissue damage and how to restore immune tolerance to cardiac tissue, before additional regenerative therapies can achieve their full potential.

Vγ1+γδT, early cardiac infiltrated innate population dominantly producing IL-4, protect mice against CVB3 myocarditis by modulating IFNγ+ T response

Viral myocarditis (VMC) is an inflammation of the myocardium closely associated with Coxsackievirus B3 (CVB3) infection. Vγ1⁺γδT cells, one of early cardiac infiltrated innate population, were reported to protect CVB3 myocarditis while the precise mechanism not fully addressed. To explore cytokine profiles and kinetics of Vγ1⁺γδT and mechanism of protection against VMC, flow cytometry was conducted on cardiac Vγ1 cells in C57BL/6 mice following CVB3 infection. The level of cardiac inflammation, transthoracic echocardiography and viral replication were evaluated after monoclonal antibody depletion of Vγ1γδT. We found that Vγ1⁺γδT cells infiltration peaked in the heart at day3 post CVB3 infection and constituted a minor source of IFN-γ but major producers for early IL-4. Vγ1γδT cells were activated earlier holding a higher IL-4-producing efficiency than CD4⁺Th cells in the heart. Depletion of Vγ1⁺γδT resulted in a significantly exacerbated cardiac infiltration, increased T, macrophage and neutrophil population in heart homogenates and worse cardiomyopathy; which was accompanied by a significant expansion of peripheral IFNγ⁺CD4+ and CD8+T cells. Neutralization of IL-4 in mice resulted in an exacerbated acute myocarditis confirming the IL-4-mediated protective mechanism of Vγ1. Our findings identify a unique property of Vγ1⁺γδT cells as one dominant early producers of IL-4 upon CVB3 acute infection which is a key mediator to protect mice against acute myocarditis by modulating IFNγ-secreting T response.

ERβ and ERα Differentially Regulate NKT and Vγ4+ T-cell Activation and T-regulatory Cell Response in Coxsackievirus B3 Infected Mice

OBJECTIVES

Coxsackievirus B3 (CVB3) induced myocarditis is sex dependent with males developing more severe disease than females. Previous studies had shown that sex-associated hormones determine the sex bias with testosterone and progesterone promoting myocarditis while estrogen (E2) is protective. There are two major estrogen receptors: estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ). The goal of the current study was to determine the relative role of these receptors to myocarditis susceptibility and the mechanism of their action.

METHODS

Female C57Bl/6 wild-type mice and C57Bl/6 mice deficient in ERα, or ERβ were infected intraperitoneally with 102 plaque forming units CVB3. After 7 days, hearts were evaluated for virus titers by plaque forming assay and myocardial inflammation. Lymphoid cells either from the spleen or infiltrating the heart were characterized by labeling with antibodies including CD4, CD25, FoxP3, IFNγ, IL-4, CD11b, CD1d, Vγ4, TCRβ, or with CD1d-tetramer and evaluated by flow cytometry. To confirm that signaling through distinct estrogen receptors controlled myocarditis susceptibility and T-regulatory cell response, male C57Bl/6 mice were treated with the ERα-specific agonist, propyl pyrazole triol (PPT), ERβ agonist, diarylpropionitrile (DPN), or 17-β-estradiol (E2) as a non-specific estrogen receptor agonist.

RESULTS

Myocarditis, cardiac virus titers, and CD4⁺ Th1 (IFNγ) bias were increased in infected ERαKO and decreased in infected ERβKO mice compared to C57Bl/6 controls. CD4⁺Th1 bias and myocarditis severity correlated inversely with numbers of CD4⁺CD25⁺FoxP3⁺ T regulatory cells which were decreased in ERαKO and increased in ERβKO mice. Increased T-regulatory cells corresponded to a preferential activation of natural killer T (NKT) cells in ERβKO mice. Male C57Bl/6 mice treated with DPN showed increased myocarditis while those treated with PPT and E2 showed decreased myocarditis corresponding to either decreased (DPN) or increased (PPT/E2) T-regulatory cell responses in male C57Bl/6 mice. DPN and PPT treatment had no effect on T-regulatory cell responses in NKT KO or γδKO mice.

CONCLUSION

These results demonstrate that ERα and ERβ both modulated CVB3 myocarditis susceptibility but in opposite directions and that their predominant effect is mediated through their ability to alter NKT and Vγ4⁺ innate T cell responses in the infected host. It is these innate T cells which positively or negatively modulate T-regulatory cell responses.

Global characterization of differential gene expression profiles in mouse Vγ1+ and Vγ4+ γδ T cells

Peripheral γδ T cells in mice are classified into two major subpopulations, Vγ1⁺ and Vγ4⁺, based on the composition of T cell receptors. However, their intrinsic differences remain unclear. In this study, we analyzed gene expression profiles of the two subsets using Illumina HiSeq 2000 Sequencer. We identified 1995 transcripts related to the activation of Vγ1⁺ γδ T cells, and 2158 transcripts related to the activation of Vγ4⁺ γδ T cells. We identified 24 transcripts differentially expressed between the two subsets in resting condition, and 20 after PMA/Ionomycin treatment. We found that both cell types maintained phenotypes producing IFN-γ, TNF-α, TGF-β and IL-10. However, Vγ1⁺ γδ T cells produced more Th2 type cytokines, such as IL-4 and IL-5, while Vγ4⁺ γδ T cells preferentially produced IL-17. Our study provides a comprehensive gene expression profile of mouse peripheral Vγ1⁺ and Vγ4⁺ γδ T cells that describes the inherent differences between them.

Proinflammatory effects of interferon gamma in mouse adenovirus 1 myocarditis

Adenoviruses are frequent causes of pediatric myocarditis. Little is known about the pathogenesis of adenovirus myocarditis, and the species specificity of human adenoviruses has limited the development of animal models, which is a significant barrier to strategies for prevention or treatment. We have developed a mouse model of myocarditis following mouse adenovirus 1 (MAV-1) infection to study the pathogenic mechanisms of this important cause of pediatric myocarditis. Following intranasal infection of neonatal C57BL/6 mice, we detected viral replication and induction of interferon gamma (IFN-γ) in the hearts of infected mice. MAV-1 caused myocyte necrosis and induced substantial cellular inflammation that was composed predominantly of CD3(+) T lymphocytes. Depletion of IFN-γ during acute infection reduced cardiac inflammation in MAV-1-infected mice without affecting viral replication. We observed decreased contractility during acute infection of neonatal mice, and persistent viral infection in the heart was associated with cardiac remodeling and hypertrophy in adulthood. IFN-γ is a proinflammatory mediator during adenovirus-induced myocarditis, and persistent adenovirus infection may contribute to ongoing cardiac dysfunction.

IMPORTANCE

Studying the pathogenesis of myocarditis caused by different viruses is essential in order to characterize both virus-specific and generalized factors that contribute to disease. Very little is known about the pathogenesis of adenovirus myocarditis, which is a significant impediment to the development of treatment or prevention strategies. We used MAV-1 to establish a mouse model of human adenovirus myocarditis, providing the means to study host and pathogen factors contributing to adenovirus-induced cardiac disease during acute and persistent infection. The MAV-1 model will enable fundamental studies of viral myocarditis, including IFN-γ modulation as a therapeutic strategy.

γδ T cell subsets play opposing roles in regulating experimental autoimmune encephalomyelitis

γδ T cells are resident in cerebrospinal fluid and central nervous system (CNS) lesions of multiple sclerosis (MS) patients, but as multifaceted cells exhibiting innate and adaptive characteristics, their function remains unknown. Previous studies in experimental autoimmune encephalomyelitis (EAE) are contradictory and identified these cells as either promoting or suppressing disease pathogenesis. This study examines distinct γδ T cell subsets during EAE and indicates they mediate differential functions in CNS inflammation and demyelination resulting in pathogenesis or protection. We identified two γδ subsets in the CNS, Vγ1(+) and Vγ4(+), with distinct cytokine profiles and tissue specificity. Anti-γδ T cell receptor (TCR) monoclonal antibody (mAb) administration results in activation and downregulation of surface TCR, rendering the cells undetectable, but with opposing effects: anti-Vγ4 treatment exacerbates disease whereas anti-Vγ1 treatment is protective. The Vγ4(+) subset produces multiple pro-inflammatory cytokines including high levels of IL-17, and accounts for 15-20% of the interleukin-17 (IL-17) producing cells in the CNS, but utilize a variant transcriptional program than CD4(+) Th17 cells. In contrast, the Vγ1 subset produces CCR5 ligands, which may promote regulatory T cell differentiation. γδ T cell subsets thus play distinct and opposing roles during EAE, providing an explanation for previous reports and suggesting selective targeting to optimize regulation as a potential therapy for MS.

c-FLIP-Short reduces type I interferon production and increases viremia with coxsackievirus B3

Cellular FLIP (c-FLIP) is an enzymatically inactive paralogue of caspase-8 and as such can block death receptor-induced apoptosis. However, independent of death receptors, c-FLIP-Long (c-FLIP_L) can heterodimerize with and activate caspase-8. This is critical for promoting the growth and survival of T lymphocytes as well as the regulation of the RIG-I helicase pathway for type I interferon production in response to viral infections. Truncated forms of FLIP also exist in mammalian cells (c-FLIP_S) and certain viruses (v-FLIP), which lack the C-terminal domain that activates caspase-8. Thus, the ratio of c-FLIP_L to these short forms of FLIP may greatly influence the outcome of an immune response. We examined this model in mice transgenically expressing c-FLIP_S in T cells during infection with Coxsackievirus B3 (CVB3). In contrast to our earlier findings of reduced myocarditis and mortality with CVB3 infection of c-FLIP_L-transgenic mice, c-FLIP_S-transgenic mice were highly sensitive to CVB3 infection as manifested by increased cardiac virus titers, myocarditis score, and mortality compared to wild-type C57BL/6 mice. This observation was paralleled by a reduction in serum levels of IL-10 and IFN-α in CVB3-infected c-FLIP_S mice. In vitro infection of c-FLIP_S T cells with CVB3 confirmed these results. Furthermore, molecular studies revealed that following infection of cells with CVB3, c-FLIP_L associates with mitochondrial antiviral signaling protein (MAVS), increases caspase-8 activity and type I IFN production, and reduces viral replication, whereas c-FLIP_S promotes the opposite phenotype.

A canonical Vγ4Vδ4+ γδ T cell population with distinct stimulation requirements which promotes the Th17 response

We previously reported a subset of γδ T cells in mice which preferentially responds following intradermal immunization with collagen in complete Freund's adjuvant (CFA). These cells express a nearly invariant "canonical" Vγ4Vδ4+ TCR. They are potent producers of IL-17A and promote the development of collagen-induced arthritis. In this study, we report that CFA emulsified with PBS alone (without collagen) is sufficient to induce a strong response of Vγ4Vδ4+ cells in the draining lymph nodes of DBA/1 and C57BL/6 mice and that the TCRs of the elicited Vγ4Vδ4+ cells in both strains heavily favor the canonical sequence. However, although both CFA and incomplete Freund's adjuvant (which lacks the killed mycobacteria present in CFA) induced Vγ4Vδ4+ γδ T cell to expand, only CFA stimulated them to express IL-17A. The route of immunization was also critical, since intraperitoneal CFA induced only a weak response by these cells, whereas intradermal or subcutaneous CFA strongly stimulated them, suggesting that the canonical CFA-elicited Vγ4Vδ4+ cells are recruited from Vγ4+ γδ T cells normally found in the dermis. Their IL-17A response requires the toll-like receptor adapter protein MyD88, and their activation is enhanced by IFNγ, although αβ T cells need not be present. The CFA-elicited Vγ4Vδ4+ γδ T cells show a cytokine profile different from that of other previously described IL-17-producing γδ T cells. Finally, the Vγ4Vδ4+ subset appears to promote the Th17 αβ T cell response, suggesting its importance in mounting an effective immune response against certain pathogens.

Cross-regulation of T regulatory-cell response after coxsackievirus B3 infection by NKT and γδ T cells in the mouse

Coxsackievirus B3 (CVB3) variants H3 and H310A1 differ by a single nonconserved amino acid in the VP2 capsid region. C57Bl/6 mice infected with the H3 virus develop myocarditis correlating with activation of T cells expressing the Vγ4 T cell receptor chain. Infecting mice with H310A1 activates natural killer T (NKT; mCD1d-tetramer(+) TCRβ(+)) cells, but not Vγ4 T cells, and fails to induce myocarditis. H310A1 infection preferentially activates M2 alternatively activated macrophage and CD4(+)FoxP3 (T regulatory) cells, whereas CD4(+)Th1 (IFN-γ(+)) cells are suppressed. By contrast, H3 virus infection activates M1 proinflammatory and CD4(+)Th1 cells, but not T regulatory cells. The M1 macrophage show significantly increased CD1d expression compared to M2 macrophage. The ability of NKT cells to suppress myocarditis was shown by adoptive transfer of purified NKT cells into H3-infected NKT knockout (Jα18 knockout) mice, which inhibited cardiac inflammation and increased T regulatory cell response. Cardiac virus titers were equivalent in all mouse strains indicating that neither Vγ4 nor NKT cells participate in control of virus infection. These data show that NKT and Vγ4 cells cross-regulate T regulatory cell responses during CVB3 infections and are the primary factor determining viral pathogenesis in this mouse model.

Comparative biology of γδ T cell function in humans, mice, and domestic animals

γδ T cells are a functionally heterogeneous population and contribute to many early immune responses. The majority of their activity is described in humans and mice, but the immune systems of all jawed vertebrates include the γδ T cell lineage. Although some aspects of γδ T cells vary between species, critical roles in early immune responses are often conserved. Common features of γδ T cells include innate receptor expression, antigen presentation, cytotoxicity, and cytokine production. Herein we compare studies describing these conserved γδ T cell functions and other, potentially unique, functions. γδ T cells are well documented for their potential immunotherapeutic properties; however, these proposed therapies are often focused on human diseases and the mouse models thereof. This review consolidates some of these studies with those in other animals to provide a consensus for the current understanding of γδ T cell function across species.

Sex-specific signaling through Toll-Like Receptors 2 and 4 contributes to survival outcome of Coxsackievirus B3 infection in C57Bl/6 mice

Background

Coxsackievirus B3 (CVB3) induces myocarditis, an inflammatory heart disease, which affects men more than women. Toll-like receptor (TLR) signaling has been shown to determine the severity of CVB3-induced myocarditis. No direct role for signaling through TLR2 had been shown in myocarditis although published studies show that cardiac myosin is an endogenous TLR2 ligand and stimulates pro-inflammatory cytokine expression by dendritic cells in vitro. The goal of this study is to determine which TLRs show differential expression in CVB3 infected mice corresponding to male susceptibility and female resistance in this disease.

Methods

Male and female C57Bl/6 mice were infected with 10² PFU CVB3 and killed on day 3 or 6 post infection. Hearts were evaluated for virus titer, myocardial inflammation, and TLR mRNA expression by PCR array and microarray analysis. Splenic lymphocytes only were evaluated by flow cytometry for the number of TLR+/CD3+, TLR+/CD4+, TLR+F4/80+ and TLR+/CD11c+ subpopulations and the mean fluorescence intensity to assess upregulation of TLR expression on these cells. Mice were additionally treated with PAM3CSK4 (TLR2 agonist) or ultrapure LPS (TLR4 agonist) on the same day as CVB3 infection or 3 days post infection to confirm their role in myocarditis susceptibility.

Results

Despite equivalent viral titers, male C57Bl/6 mice develop more severe myocarditis than females by day 6 after infection. Microarray analysis shows a differential expression of TLR2 at day 3 with female mice having higher levels of TLR2 gene expression compared to males. Disease severity correlates to greater TLR4 protein expression on splenic lymphocytes in male mice 3 days after infection while resistance in females correlates to preferential TLR2 expression, especially in spleen lymphocytes. Treating male mice with PAM reduced mortality from 55% in control CVB3 infected animals to 10%. Treating female mice with LPS increased mortality from 0% in control infected animals to 60%.

Conclusion

CVB3 infection causes an up-regulation of TLR2 in female and of TLR4 in male mice and this differential expression between the sexes contributes to disease resistance of females and susceptibility of males. While previous reports demonstrated a pathogenic role for TLR4 this is the first report that TLR2 is preferentially up-regulated in CVB3 infected female mice or that signaling through this TLR directly causes myocarditis resistance.

Slam haplotype 2 promotes NKT but suppresses Vγ4+ T-cell activation in coxsackievirus B3 infection leading to increased liver damage but reduced myocarditis

There are two major haplotypes of signal lymphocytic activation molecule (Slam) in inbred mouse strains, with the Slam haplotype 1 expressed in C57Bl/6 mice and the Slam haplotype 2 expressed in most other commonly used inbred strains, including 129 mice. Because signaling through Slam family receptors can affect innate immunity [natural killer T cell (NKT) and γ-δ T-cell receptor], and innate immunity can determine susceptibility to coxsackievirus B3 (CVB3) infection, the present study evaluated the response of C57Bl/6 and congenic B6.129c1 mice (expressing the 129-derived Slam locus) to CVB3. CVB3-infected C57Bl/6 male mice developed increased myocarditis but reduced hepatic injury compared with infected B6.129c1 mice. C57Bl/6 mice also had increased γδ(+) and CD8(+)interferon-γ(+) cells but decreased numbers of NKT (T-cell receptor β chain + mCD1d tetramer(+)) and CD4(+)FoxP3(+) cells compared with B6.129c1 mice. C57Bl/6 mice were infected with CVB3 and treated with either α-galactosylceramide, an NKT cell-specific ligand, or vehicle (dimethyl sulfoxide/PBS). Mice treated with α-galactosylceramide showed significantly reduced myocarditis. Liver injuries, as determined by alanine aminotransferase levels in plasma, were increased significantly, confirming that NKT cells are protective for myocarditis but pathogenic in the liver.

Manipulating intestinal immunity and microflora: an alternative solution to viral myocarditis?

Viral myocarditis (VMC) is an important cause of heart failure and dilated cardiomyopathy with no effective clinical diagnosis and treatment, and has been commonly associated with Coxsackievirus B3 (CVB3) infection. Current evidence from CVB3 myocarditis in mice indicates that acute myocarditis is mainly mediated by the host immune responses, including Th1, Th17 and type I macrophages. Recently, innate immunity triggered by TLR3, TLR4, TLR8 and MDA5 has also been demonstrated to participate in the induction of inflammatory cytokines in response to CVB3. Apart from the heart tissue, the intestine, which is the assumed initial infection and important replication site for CVB3, needs to be investigated, where induction of innate immunity and interactions with microflora may shape the immune response involved in the pathogenesis of VMC. This review presents recent advances in research into innate and adaptive immunity to CVB3, and provides insights into developing new strategies for the future treatment for VMC.

Close link between development and function of gamma-delta T cells

Murine γδ T cells develop as the first T-cell lineage within the fetal thymus and disproportionately localize in mucosal tissues such as lung, skin, uterus, and intestine of adult mice. These unique developmental features and distribution patterns of γδ T cells enable rapid functioning against various insults from pathogens. γδ T cells are also able to respond to local inflammation and consequently regulate the pathogenesis of autoimmune disorders and development of tumors in mice and humans. Hence, it is clinically important to understand the mechanisms that regulate γδ T cell functions. Recent evidence has shown that generations of effector γδ T cell subsets producing IFN-γ, IL-4, and IL-17 are programmed in the murine thymus before their migration to peripheral tissues. This review outlines our current understanding of the development and function of γδ T cells as they influence both innate and acquired immunity.

Sex differences in TLR2 and TLR4 expression and their effect on coxsackievirus-induced autoimmune myocarditis

Coxsackievirus B3 (CVB3) infection of C57Bl/6 mice shows a sex bias with males developing more severe cardiac inflammation than females because males develop a Th1 inflammatory response, whereas females develop a Th2 response. Since their discovery, Toll-like receptors have been shown to play an important role in the development of the immune response against harmful pathogens. To assess the role of TLRs in coxsackievirus-induced myocarditis wild type and Toll-like receptor 2-/- male and female mice were infected and assessed for viral replication, myocarditis, helper T-cell generation, and regulatory T-cell generation. TLR2-/- mice show reduced Th1 expression compared to controls. Treatment of wild type mice with either Pam3CSK4 (TLR2) or LPS (TLR4) specific TLR agonists resulted in increased Th1 expression in male and female mice and a decrease in FoxP3+ regulatory T-cells in male mice. The suppression of T regulatory cells by TLR signaling in males but not females correlates with the increased myocarditis susceptibility of the males.

IL-21R expression on CD8+ T cells promotes CD8+ T cell activation in coxsackievirus B3 induced myocarditis

IL-21 is a multi-functional cytokine which can promote survival, proliferation and activation of T and B lymphocytes including CD8 T cells. Previous studies have shown that autoimmune CD8+ T cells are the primary pathogenic effector cell in coxsackievirus B3 (CVB3) induced myocarditis in C57Bl/6 mice. To evaluate the role of IL-21 in promoting CD8+ T cell mediated cardiac injury in myocarditis, C57Bl/6 and IL-21RKO mice were infected with CVB3. IL-21RKO mice developed significantly less myocarditis than C57Bl/6 animals although cardiac virus titers were equivalent between the mouse strains. Numbers of CD8+IFNγ+ cells were decreased in IL-21RKO mice but numbers of either CD4+IFNγ+ or CD4+IL-4+ cells were not significantly different from C57Bl/6 animals indicating a selective effect of IL-21 signaling on the CD8+ T cell response. To confirm that IL-21 signaling exclusively functions at the level of the CD8+ T cell in CVB3 induced myocarditis, purified CD8+ cells were isolated from either C57Bl/6 or IL-21RKO donors and adoptively transferred into CD8KO recipients prior to CVB3 infection. CD8KO recipients given either C57Bl/6 or IL-21RKO CD8+ cells showed equivalent reconstitution of the CD8+ cells in the spleen but the recipients given C57Bl/6 CD8+ cells showed significantly greater myocarditis than recipients of IL-21RKO CD8+ cells. These data demonstrate that IL-21 signaling directly in the CD8+ cell population is required for CVB3-induced myocarditis.

αβ TCR⁺ T cells, but not B cells, promote autoimmune keratitis in b10 mice lacking γδ T cells

PURPOSE

To investigate additional factors in the spontaneous development of keratitis previously reported in B10.TCRδ⁻/⁻ female mice.

METHODS

The study tested whether susceptible B10.TCRδ⁻/⁻ mice have dry eyes compared with resistant B6.TCRδ⁻/⁻ females and also rederived the B10.TCRδ⁻/⁻ strain to test for the role of an infectious agent. Also assessed was whether adoptive transfer of αβ T cells from autoimmune mice induced keratitis in resistant mice. In addition, a potential role was examined for B cells or autoantibodies by B-cell inactivation, and the role of female hormones was tested by ovariectomy. Finally, the study investigated whether adoptive transfer of Vγ1⁺ γδ T cells confers protection.

RESULTS

Tear production in B10.TCRδ⁻/⁻ females was actually higher than in B6.TCRδ⁻/⁻ controls. Rederived B10.TCRδ⁻/⁻ mice still developed keratitis. Keratitis was induced in resistant mice after adoptive transfer of αβ T cells from keratitic donors. Inactivation of B cells from susceptible mice had no effect on the development of keratitis. Ovariectomy did not significantly reduce disease in B10.TCRδ⁻/⁻ females. Adoptive transfer of Vγ1⁺ cells from wild-type donors reduced keratitis in B10.TCRδ⁻/⁻ females.

CONCLUSIONS

Neither low tear levels nor ovarian hormones contribute to spontaneous keratitis in B10.TCRδ⁻/⁻ female mice, nor does it appear to depend on an infectious agent carried vertically in this strain. However, αβ T cells from keratitic hosts are sufficient to induce disease in the resistant B10.TCRβ⁻/⁻δ⁻/⁻ strain. Autoaggressive αβ T cells in the absence of Vγ1⁺ T cells in B10.TCRδ⁻/⁻ mice may be insufficiently checked to prevent disease.

Chromosome y regulates survival following murine coxsackievirus b3 infection

Coxsackievirus B3 (CVB3) contributes to the development of myocarditis, an inflammatory heart disease that predominates in males, and infection is a cause of unexpected death in young individuals. Although gonadal hormones contribute significantly to sex differences, sex chromosomes may also influence disease. Increasing evidence indicates that Chromosome Y (ChrY) genetic variants can impact biological functions unrelated to sexual differentiation. Using C57BL/6J (B6)-ChrY consomic mice, we show that genetic variation in ChrY has a direct effect on the survival of CVB3-infected animals. This effect is not due to potential Sry-mediated differences in prenatal testosterone exposure or to differences in adult testosterone levels. Furthermore, we show that ChrY polymorphism influences the percentage of natural killer T cells in B6-ChrY consomic strains but does not underlie CVB3-induced mortality. These data underscore the importance of investigating not only the hormonal regulation but also ChrY genetic regulation of cardiovascular disease and other male-dominant, sexually dimorphic diseases and phenotypes.

Histamine H(1) receptor signaling regulates effector T cell responses and susceptibility to coxsackievirus B3-induced myocarditis

Susceptibility to autoimmune myocarditis has been associated with histamine release by mast cells during the innate immune response to coxsackievirus B3 (CVB3) infection. To investigate the contribution of histamine H(1) receptor (H(1)R) signaling to CVB3-induced myocarditis, we assessed susceptibility to the disease in C57BL/6J (B6) H(1)R(-/-) mice. No difference was observed in mortality between CVB3-infected B6 and H(1)R(-/-) mice. However, analysis of their hearts revealed a significant increase in myocarditis in H(1)R(-/-) mice that is not attributed to increased virus replication. Enhanced myocarditis susceptibility correlated with a significant expansion in pathogenic Th1 and Vγ4(+) γδ T cells in the periphery of these animals. Furthermore, an increase in regulatory T cells was observed, yet these cells were incapable of controlling myocarditis in H(1)R(-/-) mice. These data establish a critical role for histamine and H(1)R signaling in regulating T cell responses and susceptibility to CVB3-induced myocarditis in B6 mice.

Regulation and function of IL-17A- and IL-22-producing γδ T cells

The regulation of IL-17A and IL-22 production differs between human and murine γδ T cells. We find that human γδ T cells expressing Vγ2Vδ2 T cell receptors are peripherally polarized to produce IL-17A or IL-22, much like CD4 αβ Th17 T cells. This requires IL-6, IL-1β, and TGF-β, whereas expansion and maintenance requires IL-23, IL-1β, and TGF-β. In contrast, IL-17A and IL-22 production by murine γδ T cells is innately programmed during thymic ontogeny but requires IL-23 and IL-1β for maintenance. Murine γδ cells producing IL-17A and IL-22 play important roles in microbial, autoimmune, and inflammatory responses. However, the roles played by human IL-17A- and IL-22-producing γδ T cells are less clear but are also likely to be important. These observations highlight differences between humans and murine γδ T cells and underscore the importance of IL-17A- and IL-22-producing γδ T cells.

Role of γδ T cells in antibody production and recovery from SFV demyelinating disease

Semliki Forest Virus (SFV) encephalomyelitis has been used to study the pathogenesis of virus-induced demyelination and serves as a model for multiple sclerosis. SFV-infection of mice invariably leads to clinical weakness accompanied by CNS inflammation, viral clearance and primary demyelination by day 21 postinfection (pi), followed by recovery and remyelination by day 35 pi. We have applied this model to the examination of the effects of γδ T cells in antibody production and the pathogenesis of demyelinating lesions. SFV-infection of γδ T cell KO mice resulted in more severe clinical signs than in wild type (WT) B6 mice. SFV-infected WT and γδ KO mice both cleared virus by day 10 pi and inflammation was comparable. Demyelination also appeared to be similar in both groups except that KO mice did not exhibit extensive remyelination which was seen in WT mice by day 21. SFV-infected WT mice showed widespread remyelination by day 35 pi, whereas KO mice still displayed some demyelination through day 42 pi. Both WT and KO mice developed serum antibodies to SFV. However, the reactivity of WT sera with the SFV epitope, E2 T(h) peptide₂, was significantly higher than in KO sera. Immunization with E2 T(h) peptide₂ resulted in elevated antibody production to this peptide (p<0.05) and earlier remyelination (day 28 pi) in KO mice. Thus, our study has shown for the first time that immunization of SFV-infected γδ T cell KO mice with a viral peptide, E2 T(h) peptide₂ led to enhanced recovery and repair of the CNS.

Cross-talk between cd1d-restricted nkt cells and γδ cells in t regulatory cell response

CD1d is a non-classical major histocompatibility class 1-like molecule which primarily presents either microbial or endogenous glycolipid antigens to T cells involved in innate immunity. Natural killer T (NKT) cells and a subpopulation of γδ T cells expressing the Vγ4 T cell receptor (TCR) recognize CD1d. NKT and Vγ4 T cells function in the innate immune response via rapid activation subsequent to infection and secrete large quantities of cytokines that both help control infection and modulate the developing adaptive immune response. T regulatory cells represent one cell population impacted by both NKT and Vγ4 T cells. This review discusses the evidence that NKT cells promote T regulatory cell activation both through direct interaction of NKT cell and dendritic cells and through NKT cell secretion of large amounts of TGFβ, IL-10 and IL-2. Recent studies have shown that CD1d-restricted Vγ4 T cells, in contrast to NKT cells, selectively kill T regulatory cells through a caspase-dependent mechanism. Vγ4 T cell elimination of the T regulatory cell population allows activation of autoimmune CD8+ effector cells leading to severe cardiac injury in a coxsackievirus B3 (CVB3) myocarditis model in mice. CD1d-restricted immunity can therefore lead to either immunosuppression or autoimmunity depending upon the type of innate effector dominating during the infection.

Characterization of avian γδ T-cell subsets after Salmonella enterica serovar Typhimurium infection of chicks

Avian γδ T lymphocytes are frequently found in blood and organs and are assumed to be crucial to the immune defense against Salmonella infections of chicks. To elucidate the so-far-unknown immunological features of subpopulations of avian γδ T cells in the course of infection, day-old chicks were infected orally with Salmonella enterica serovar Typhimurium. Until 11 days after infection, the occurrence as well as transcription of the CD8 antigen and immunologically relevant protein genes of CD8α(-) and CD8α(+high) (CD8αα(+) CD8αβ(+)) γδ cells were analyzed using flow cytometry and quantitative real-time reverse transcription-PCR (RT-PCR) with blood, spleen, thymus, and cecum samples. After infection, an increased percentage of CD8α(+high) γδ T lymphocytes was found in blood, in spleen, and, with the highest values and most rapidly, in cecum. Within the CD8α(+high) subset, a significant rise in the number of CD8αα(+) cells was accompanied by enhanced CD8α antigen expression and reduced gene transcription of the CD8β chain. CD8αα(+) and CD8αβ(+) cells showed elevated transcription for Fas, Fas ligand (FasL), interleukin-2 receptor α (IL-2Rα), and gamma interferon (IFN-γ). While the highest fold changes in mRNA levels were observed in CD8αβ(+) cells, the mRNA expression rates of CD8αβ(+) cells never significantly exceeded those of the CD8αα(+) cells. In conclusion, both CD8α(+high) γδ T-cell subpopulations (CD8αα(+) and CD8αβ(+)) might be a potential source of IFN-γ in Salmonella-infected chicks. However, due to their prominent frequency in blood and organs after infection, the avian CD8αα(+) γδ T-cell subset seems to be unique and of importance in the course of Salmonella Typhimurium infection of very young chicks.

Type B coxsackieviruses and their interactions with the innate and adaptive immune systems

Coxsackieviruses are important human pathogens, and their interactions with the innate and adaptive immune systems are of particular interest. Many viruses evade some aspects of the innate response, but coxsackieviruses go a step further by actively inducing, and then exploiting, some features of the host cell response. Furthermore, while most viruses encode proteins that hinder the effector functions of adaptive immunity, coxsackieviruses and their cousins demonstrate a unique capacity to almost completely evade the attention of naive CD8(+) T cells. In this artcle, we discuss the above phenomena, describe the current status of research in the field, and present several testable hypotheses regarding possible links between virus infection, innate immune sensing and disease.

γδ T lymphocytes kill T regulatory cells through CD1d

Coxsackievirus B3 (CVB3) induces myocarditis, an inflammation of the myocardium, in C57Bl/6 male mice but not in mice lacking γδ+ T cells [γδ knockout (γδKO)]. Suppression of myocarditis in γδKO mice corresponds to an increase in CD4(+) CD25(+) FoxP3(+) T regulatory cells. A subpopulation of the T regulatory cells in infected γδKO mice expressed high levels of CD1d, a non-classical major histocompatibility complex class 1-like molecule. Adoptive transfer of CD1d(+) and CD1d(-) CD4(+) CD25(+) cells into infected C57Bl/6 recipients showed that the CD1d(+) subpopulation is substantially more suppressive than the CD1d(-) subpopulation. T cells expressing the γδ T-cell receptor comprised approximately 30-50% of the infiltrating lymphoid cells in the hearts of myocarditic C57Bl/6 mice and approximately half of the γδ+ cells expressed the Vγ4 T-cell receptor. The Vγ4+ cells lysed T regulatory cells from γδKO mice but not from wild-type (C57Bl/6) animals. Lysis was inhibited by antibody to CD1d and zVAD-fmk, a pan-caspase inhibitor. The Vγ4-γδ+ cells were not lytic to T regulatory cells and did not promote myocarditis. These results demonstrate that Vγ4+ cells selectively abrogate T regulatory cells through recognition of CD1d expressed on the regulatory cells and caspase-dependent apoptosis.

Depletion of gammadelta+ T cells increases CD4+ FoxP3 (T regulatory) cell response in coxsackievirus B3-induced myocarditis

Coxsackievirus B3 (CVB3) causes severe myocarditis in BALB/c mice which depends upon CD4(+) T helper type 1 [Th1; i.e. interferon-gamma(+) (IFN-gamma(+))] and gammadelta(+) cells. Depleting gammadelta(+) cells using anti-gammadelta antibody suppresses myocarditis and CD4(+) IFN-gamma(+) cell numbers in the spleen and heart of infected mice while increasing CD4(+) FoxP3(+) cells. Mice deficient in gammadelta(+) cells have increased numbers of naïve (CD44(lo) CD62L(hi)) and fewer effector (CD44(hi) CD62(lo)) memory CD4(+) cells than infected gammadelta(+)-cell-sufficient mice. Virus neutralizing antibody titres are not significantly different between gammadelta(+) T-cell-sufficient and -deficient animals. To confirm that the memory cell response differs in acutely infected mice lacking gammadelta(+) cells, CD4(+) cells were purified and adoptively transferred into naïve recipients, which were rested for 4 weeks then infected with CVB3. Recipients given either 0.5 x 10(6) or 1.0 x 10(6) CD4(+) from infected donors developed over twice the severity myocarditis and 10-fold less cardiac virus titre compared with recipients given equivalent numbers of CD4(+) cells from infected and gammadelta(+)-cell-depleted donor animals. Additionally, to show that more functionally active T regulatory cells are present in gammadelta(+) T-cell-depleted mice, CD4(+) CD25(+) and CD4(+) CD25(-) cells were isolated and adoptively transferred into infected recipients. Mice receiving CD4(+) CD25(+) cells from gammadelta(+) T-cell-depleted donors developed significantly less myocarditis and CD4(+) Th1 cell responses compared with mice receiving equal numbers of CD4(+) CD25(+) cells from infected gammadelta(+) T-cell-sufficient animals. This study shows that gammadelta(+) cells promote CD4(+) IFN-gamma(+) acute and memory responses by limiting FoxP3(+) T regulatory cell activation.

Response of gammadelta T Cells to plant-derived tannins

Many pharmaceutical drugs arc isolated from plants used in traditional medicines, and new plant-derived pharmaceutical drugs continue to be identified. Relevant to this review, different plant-derived agonists for gammadelta T cells are described that impart effector functions upon distinct subsets of these cells. Recently, plant tannins have been defined as one class of gammadelta T cell agonist and appear to preferentially activate the mucosal population. Mucosal gammadelta T cells function to modulate tissue immune responses and induce epithelium repair. Select tannins, isolated from apple peel, rapidly induce immune gene transcription in gammadelta T cells, leading to cytokinc production and increased responsiveness to secondary signals. Activity of these tannin preparations tracks to the procyanidin fraction, with the procyanidin trimer (C1) having the most robust activity defined to date. The response to the procyanidins is evolutionarily conserved in that responses are seen with human, bovine, and murine gammadelta T cells, although human cells show less selectivity. Procyanidin-induced responses described in this review likely account for the expansion of mucosal gammadelta T cells seen in mice and rats fed soluble extracts of tannins. Use of procyanidins to activate gammadelta T cells may represent a novel approach for the treatment of tissue damage and autoimmune diseases.

Coxsackievirus B3 induction of NFAT: requirement for myocarditis susceptibility

Ultraviolet (u.v.) inactivated coxsackievirus B3 (CVB3) induces rapid calcium flux in naïve BALB/c CD4+ T cells. CD4+ cells lacking decay accelerating factor (DAF-/-) show little calcium flux indicating that virus cross-linking of this virus receptor protein is necessary for calcium signaling in CVB3 infection. Interaction of CVB3 with CD4+ cells also activates NFAT DNA binding. To show that NFAT activation is crucial to CVB3 induced disease, wild-type mice and transgenic mice expressing dominant-negative NFAT (dnNFAT) mutant in T cells were infected and evaluated for myocarditis and pancreatitis 7 days later. Inhibition of NFAT in T cells prevented myocarditis but had no effect on pancreatitis. Virus titers in pancreas were equivalent in wild-type and dnNFAT animals but cardiac virus titers were increased in dnNFAT mice. Interferon-gamma (IFN gamma) expression was reduced in both CD4+ and V gamma 4+ T cells from dnNFAT mice compared to controls. FasL expression by V gamma 4+ cells was also suppressed. Inhibition of FasL expression by V gamma 4+ cells is consistent with myocarditis protection in dnNFAT mice.

Coxsackievirus B3-induced myocarditis: infection of females during the estrus phase of the ovarian cycle leads to activation of T regulatory cells

Transgenic female mice expressing the TNFalpha gene under the cardiac myosin promoter (TNF1.6) develop substantially increased myocarditis and increased numbers of CD4+Th1 (interferon gamma+) cells when infected with coxsackievirus B3 (CVB3) during the diestrus and proestrus phases of the estrus cycle compared to females infected during the estrus and metestrus phases. Cardiac virus titers were increased in females infected in estrus compared to females infected during the other phases. T regulatory cells (CD4+CD25+FoxP3+) were increased in both peripheral blood and inflammatory cells in the heart in females infected during estrus. Exogenous administration of 200 ng/mouse 17-beta-estradiol to females protected against CVB3 induced myocarditis and increased CD4+CD25+FoxP3+ cells. These results demonstrate that hormonal fluctuations occurring in normally cycling females can determine T regulatory cell response and control virus-induced pathogenesis.

Amelioration of coxsackievirus B3-mediated myocarditis by inhibition of tissue inhibitors of matrix metalloproteinase-1

Coxsackievirus B3 (CVB3) is a major cause of acute myocarditis, a serious condition that is refractory to treatment. Myocardial damage results in tissue remodeling that, if too extensive, may contribute to disease. Remodeling is achieved by extracellular proteolysis mediated by the matrix metalloproteinases (MMPs), and MMP activity is counterbalanced by tissue inhibitors of MMPs (TIMPs). We show herein that TIMP-1 expression is induced in the myocardium by CVB3 infection. Surprisingly, TIMP-1 knockout mice exhibited a profound attenuation of myocarditis, with increased survival. The amelioration of disease in TIMP-1 knockout mice was not attributable to either an altered T-cell response to the virus or to reduced viral replication. These data led us to propose a novel function for TIMP-1: its highly localized up-regulation might arrest the MMP-dependent migration of inflammatory cells at sites of infection, thereby anatomically focusing the adaptive immune response. The benefits of TIMP-1 blockade in treating viral myocarditis were confirmed by administering, to wild-type animals, TIMP-1-specific siRNA or polyclonal antisera, both of which diminished CVB3-induced myocarditis. These unexpected findings indicate that increased TIMP-1 expression exacerbates, rather than ameliorates, CVB3-induced myocarditis and, thus, that TIMP-1 may represent a target for the treatment of virus-induced heart disease.

Exacerbation of collagen-induced arthritis by oligoclonal, IL-17-producing gamma delta T cells

Murine gammadelta T cell subsets, defined by their Vgamma chain usage, have been shown in various disease models to have distinct functional roles. In this study, we examined the responses of the two main peripheral gammadelta T cell subsets, Vgamma1(+) and Vgamma4(+) cells, during collagen-induced arthritis (CIA), a mouse model that shares many hallmarks with human rheumatoid arthritis. We found that whereas both subsets increased in number, only the Vgamma4(+) cells became activated. Surprisingly, these Vgamma4(+) cells appeared to be Ag selected, based on preferential Vgamma4/Vdelta4 pairing and very limited TCR junctions. Furthermore, in both the draining lymph node and the joints, the vast majority of the Vgamma4/Vdelta4(+) cells produced IL-17, a cytokine that appears to be key in the development of CIA. In fact, the number of IL-17-producing Vgamma4(+) gammadelta T cells in the draining lymph nodes was found to be equivalent to the number of CD4(+)alphabeta(+) Th-17 cells. When mice were depleted of Vgamma4(+) cells, clinical disease scores were significantly reduced and the incidence of disease was lowered. A decrease in total IgG and IgG2a anti-collagen Abs was also seen. These results suggest that Vgamma4/Vdelta4(+) gammadelta T cells exacerbate CIA through their production of IL-17.

Plasmodium berghei XAT: contribution of gammadelta T cells to host defense against infection with blood-stage nonlethal malaria parasite

We examined a potential role of gammadelta T cells in protective immunity to blood-stage Plasmodium berghei XAT infection. Plasmodium berghei XAT is an attenuated variant of the lethal strain P. berghei NK65 and its infection is self-resolving in immune competent mice. To determine whether gammadelta T cells are essential for the resolution of P. berghei XAT malaria, mice were depleted of gammadelta T cells with anti-TCRgammadelta antibody treatment. Although mice that had received control antibody resolved infections, mice received anti-TCRgammadelta antibody could not control their infections and eventually died. Spleen cells from infected mice produced IFN-gamma and nitric oxide (NO) within the first week of infection, however, levels of IFN-gamma and NO in gammadelta T cell-depleted mice were significantly lower than in control mice. To examine whether gammadelta T cells are involved in the antibody production, malarial-specific antibodies of the various isotypes were measured in the sera of gammadelta T cell-depleted mice and control mice. Serum levels of IgG2a, which was known to be a protective antibody in P. berghei XAT malaria, were significantly lower in gammadelta T cell-depleted mice than in control mice, whereas levels of IgG1 were comparable to those in control mice. Our results indicated that the presence of the gammadelta T cell subset was essential for resolution of blood-stage P. berghei XAT malaria and played a modulatory role in the development of Th1 response and host defense against this malarial parasites.

gammadelta T-cell receptors: functional correlations

The gammadelta T-cell receptors (TCRs) are limited in their diversity, suggesting that their natural ligands may be few in number. Ligands for gammadeltaTCRs that have thus far been determined are predominantly of host rather than foreign origin. Correlations have been noted between the Vgamma and/or Vdelta genes a gammadelta T cell expresses and its functional role. The reason for these correlations is not yet known, but several different mechanisms are conceivable. One possibility is that interactions between particular TCR-V domains and ligands determine function or functional development. However, a recent study showed that at least for one ligand, receptor specificity is determined by the complementarity-determining region 3 (CDR3) component of the TCR-delta chain, regardless of the Vgamma and/or Vdelta. To determine what is required in the TCR for other specificities and to test whether recognition of certain ligands is connected to cell function, more gammadeltaTCR ligands must be defined. The use of recombinant soluble versions of gammadeltaTCRs appears to be a promising approach to finding new ligands, and recent results using this method are reviewed.

Accumulation of gamma/delta T cells in the lungs and their roles in neutrophil-mediated host defense against pneumococcal infection

The present study was designed to elucidate the role of Vgamma4(+) gammadelta T cells, a major subset of pulmonary gammadelta T cells, in host defense against infection with Streptococcus pneumoniae. The proportion and number of whole gammadelta T cells, identified as CD3(+) and TCR-delta(+) cells, and Vgamma4(+) gammadelta T cells, identified as CD3(+) and TCR-Vgamma4(+) cells, increased in the lungs at 3, 6 and 12h post-infection. Survival of infected mice and lung bacterial clearance were severely impaired in TCR-Vgamma4(-/-) mice compared with control wild-type (WT) mice. The impaired host protection in TCR-Vgamma4(-/-) mice correlated well with attenuated recruitment of neutrophils in lungs. MIP-2 and TNF-alpha synthesis in the infected tissues was significantly reduced in TCR-Vgamma4(-/-) mice compared with WT mice. Similar results were noted in the synthesis of TNF-alpha, but not clearly of MIP-2, by lung leukocytes stimulated with live bacteria. Our results demonstrate that Vgamma4(+) gammadelta T cells play an important role in the neutrophil-mediated host defense against S. pneumoniae infection by promoting the synthesis of TNF-alpha and possibly of MIP-2 in the lungs.

Cardiac and Skin Xenograft Survival in Different Recipient Mouse Strains

BACKGROUND

There are conflicting reports on the importance of antibody and cell-mediated mechanisms and the influence of TH1 or TH2 cytokines on acute vascular xenograft rejection. We sought to resolve some of the recent discrepancies in the rat-to-mouse xenograft model where different recipient strains are used and investigated the TH1/TH2 influence on rejection.

METHODS

Lewis rat heart xenograft survival was compared between BALB/c and C57BL/6 recipients. Antigraft antibody deposition, serum anti-rat antibody levels and B-cell deficient recipients were used to examine the contribution of antibody to rejection. To further investigate a TH1 or TH2 bias effect in vivo, we used BALB/c STAT4 knockout (KO) and STAT6 KO recipient mice. Experiments were repeated with rat skin xenografts to examine TH1/TH2 influences on cell-mediated rejection.

RESULTS

The median survival (MS) of rat heart xenografts in BALB/c and C57BL/6 mice was five and eight days, respectively (P = 0.002). The MS in B-cell deficient mice was 16 days (P < 0.001). The MS in STAT4 KO and STAT6 KO mice was six and seven days respectively (P = 0.009). All non-B-cell deficient recipients showed strong IgM deposition and histological features of both cellular and antibody-mediated rejection. There was no correlation between serum anti-rat antibody levels and graft outcome or graft deposition. There was no survival difference of skin xenografts in BALB/c, C57BL/6, B-cell deficient, STAT6 KO, or STAT4 KO mice (8-9 days).

CONCLUSIONS

Both humoral and cell-mediated immunity have significant roles in vascularized heart xenograft rejection. TH1/TH2 biases minimally affect rejection through humoral but not cellular immunity.

Coxsackievirus B3 induces T regulatory cells, which inhibit cardiomyopathy in tumor necrosis factor-alpha transgenic mice

Innate immunity promotes both the generation of autoimmunity and immunoregulation of adaptive immunity. Transgenic mice expressing the tumor necrosis factor-alpha (TNF-alpha) gene under the cardiac myosin promoter (TNF1.6 mice) develop dilated cardiomyopathy. Transgenic mice show extensive cardiac inflammation, suggesting that immunopathogenic mechanisms may promote cardiomyopathy. Two coxsackievirus B3 (CVB3) variants infect and replicate in the heart. H3 variant is highly myocarditic, but H310A1 variant activates CD4(+) T regulatory cells, which protect against viral myocarditis. T-cell depletion of TNF1.6 mice using monoclonal anti-CD3 or anti-CD4 antibody significantly reduced heart size and plasma troponin I concentrations compared with control TNF1.6 mice. Cardiomyopathy in TNF1.6 mice correlates to a CD4(+)Th1 response and autoimmune IgG2a antibodies. TNF1.6 mice infected with H310A1 virus reduced heart size and cardiac inflammation corresponding to the activation of CD4(+)CD25(+)FoxP3(+) (T regulatory cells). Immunosuppression is dependent on IL-10 but not TGFbeta. Adoptive transfer of the CD4(+)CD25(+) cells from H310A1-infected mice into uninfected TNF1.6 recipients abrogated cardiomyopathy. Exogenous administration of recombinant TNF-alpha to H310A1-infected mice for 4 days abrogated immunosuppression. Cardiac enlargement in TNF1.6 mice is partly attributable to T-cell activation and humoral autoimmunity caused by cytokine expression. T regulatory cells induced by H310A1 virus abrogate autoimmunity caused by TNF-alpha overexpression. H3 virus infection induces high levels of systemic TNF-alpha, whereas H310A1 virus does not. The low TNF-alpha response during H310A1 infections is likely responsible for the T regulatory cell response in these animals.

Coxsackievirus myocarditis: interplay between virus and host in the pathogenesis of heart disease

Coxsackievirus (CVB) infection is a significant cause of myocarditis and dilated cardiomyopathy (DCM). Heart disease may be caused by direct cytopathic effects of the virus, a pathologic immune response to persistent virus, or autoimmunity triggered by the viral infection. CVB interacts with its host at multiple stages during disease development. Signaling through viral receptors may alter the intracellular environment in addition to facilitating virus entry. Viral genetic determinants that encode cardiovirulence have been mapped and may change depending on the nutritional status of the host. Virus persistence is directly associated with pathology, and recent work demonstrates that CVB evolves into a slowly replicating form capable of establishing a low-grade infection in the heart. The innate immune response to CVB has taken on increasing importance because of its role in shaping the development of the adaptive immune response that is responsible for cardiac pathology. Studies of T cell responsiveness and the development of autoimmunity at the molecular level are beginning to clarify the mechanisms through which CVB infection causes inflammatory heart disease.

Evidence for the opposing roles of different gamma delta T cell subsets in macrophage homeostasis

To ensure invading pathogens are eliminated with minimal damage to host tissues it is essential that macrophage activation be tightly regulated. Previously we demonstrated that a subset of gammadelta T cells (Vgamma1(+)) contributes to resolving pathogen-induced immune responses by killing activated macrophages. However, the exaggerated macrophage response seen in infected Vgamma1(+) T cell-deficient mice suggests that gammadelta T cells play a broader role in macrophage homeostasis and other subsets might promote macrophage activation. Using a macrophage:gammadelta T cell co-culture system we have shown that gammadelta T cells increase the activity of macrophages activated in vivo by Listeria monocytogenes infection. In a dose-dependent manner, gammadelta T cells up-regulated production of cytokines (TNF-alpha, IL-6, IL-10) and chemokines (MIP-1alpha, MIP-1beta) by Listeria-elicited macrophages. The ability to increase macrophage cytokine production was prominent among Vgamma4(+) gammadelta T cells. Reciprocally, Vgamma4(+) gammadelta T cells were activated by Listeria-elicited macrophages, resulting in production of the anti-inflammatory cytokine, IL-10. gammadelta T cell adoptive transfer experiments showed that Vgamma4(+) T cells protected TCRdelta(-/-) mice against Listeria-induced liver injury and necrosis. These findings identify distinct and non-overlapping roles for gammadelta T cell subsets in regulating macrophage function during pathogen-induced immune responses.

T cells expressing the Vgamma1 T-cell receptor enhance virus-neutralizing antibody response during coxsackievirus B3 infection of BALB/c mice: differences in male and female mice

Coxsackievirus B3 infection causes severe cardiac inflammation in male but not female mice. CD3+ T cells and T cells expressing the Vgamma4 T cell receptor (TCR) predominate in the cardiac inflammatory cell infiltrate in infected male BALB/c mice. Infected females have mostly CD19+ (B lymphocyte) and Vgamma1+ cells. No significant differences in CD11b+ (monocyte) cells were observed between the sexes. Infected males showed a predominant CD4+Th1 (IFNgamma+) response, whereas females showed a predominant CD4+Th2 response. The importance of IFNgamma for myocarditis susceptibility and IL-4 for protection was confirmed using IFN-gamma-/- and IL-4-/- mice. Antibody depletion of Vgamma1+ cells augmented myocarditis susceptibility, whereas antibody depletion of Vgamma4+ cells was protective. Cardiac virus titers inversely correlated with virus neutralizing antibodies and showed that Vgamma1+ cells are important for virus neutralizing antibody response. IFNgamma affected the Vgamma4+ cell response in the heart, as IFNgamma-/- mice had few Vgamma4+ cells; but exogenous administration of recombinant IFNgamma to IFNgamma-/- mice restored myocarditis susceptibility, Th1 bias, and Vgamma4+ cell infiltration of the myocardium. These results demonstrate that two gammadelta+ T cell populations, Vgamma1+ and Vgamma4+, have different functions during myocarditis, in that Vgamma1+ cells promote humoral immunity and protection whereas Vgamma4+ cells are pathogenic.

Decay-Accelerating Factor (CD55) Promotes CD1d Expression and Vγ4+ T-Cell Activation in Coxsackievirus B3-Induced Myocarditis

BALB/c mice infected with the H3 variant of Coxsackievirus B3 (CVB3) develop severe myocarditis which is initiated by up-regulation of CD1d during infection and CD1d-dependent activation of T cells expressing the Vgamma4 T cell receptor. Previous studies have shown that a mutant variant of the H3 virus which shows reduced binding avidity to one of the known CVB3 virus receptors, decay accelerating factor (DAF), fails to up-regulate CD1d or activate Vgamma4+ cells. To determine if DAF has a role in CD1d expression during infection or Vgamma4+ cell activation, BALB/c and BALB/c DAF-/- mice were infected with CVB3. Infected DAF-/- mice show modest increases in CD1d expression compared to infected wild-type BALB/c mice; and although total numbers of Vgamma4+ cells in the spleen are the same as in BALB/c mice, few Vgamma4+ IFNgamma+ cells are detected in infected DAF-/- animals. Vgamma4+ cell depletion protects infected BALB/c mice from myocarditis but does not protect infected DAF-/- animals, indicating that Vgamma4+ cells are not important to disease in these animals. Anti-CD8 depletion of CD8+ T cells protects infected BALB/c mice but aggravates disease in infected DAF-/- animals, indicating that the immunopathogenicity of viral myocarditis differs in the absence of the DAF virus receptor.

CD1d expression on hemopoietic cells promotes CD4+ Th1 response in coxsackievirus B3 induced myocarditis

Coxsackievirus B3 induced murine myocarditis depends upon CD1d expression and upon a population of CD1d-restricted Vgamma4+ T cells. Infection upregulates CD1d expression in CD4+ T cells. Bone marrow chimeras were made between BALB/c and BALB/c CD1d-/- mice and showed that CD1d expression in either hemopoietic and non-hemopoietic cells induces myocarditis, although CD1d expression on hemopoietic cells was more effective in increasing Vgamma4+ cell numbers and activation, and CD4+ IFNgamma+ cell response than CD1d expression on non-hemopoietic cells. Co-culture of enriched CD4+ cells from infected CD1d-/- and BALB/c mice with Vgamma4+ T cells demonstrated that the Vgamma4+ cells bias the CD4+ cell response to the Th1 phenotype through CD1d. Anti-CD1d antibody effectively blocked promotion of IFNgamma expression by the CD4+ cell population. These results show that Vgamma4+ cells modulate developing adaptive immunity through recognition of CD1d on CD4+ T cells, and that this interaction, more than Vgamma4+ cell interaction with infected cardiocytes, determines pathogenicity.

A requirement for the Vgamma1+ subset of peripheral gammadelta T cells in the control of the systemic growth of Toxoplasma gondii and infection-induced pathology

gammadelta T cells are a diverse population of T cells that are widely distributed and are a common feature of pathogen-induced immune responses. It is not clear, however, whether different populations of gammadelta T cells have specific functions, and what factors determine the functional properties of individual populations. A murine model of peroral Toxoplasma gondii infection was used to determine the contribution Vgamma1+ intestinal intraepithelial lymphocytes (IELs) vs systemic Vgamma1+ T cells make to the acute and chronic stages of the host immune response, and whether the macrophage cytocidal activity of Vgamma1+ T cells described in bacterial infections is seen in other, unrelated infectious disease models. In response to oral infection with virulent type 1 or avirulent type II strains of T. gondii, TCR-delta-/- mice rapidly developed severe ileitis. In contrast, in mice deficient in Vgamma1+ T cells and IELs and wild-type mice, inflammation was delayed in onset and less severe. The protective effect of (Vgamma1-) IELs to Toxoplasma infection was unrelated to their cytolytic and cytokine (Th1)-producing capabilities. Systemic Vgamma1+ T cells were shown to play an essential role in limiting parasite growth and inflammation in peripheral tissues and, in particular, in the CNS, that was associated with their ability to efficiently kill parasite-elicited and infected macrophages. These findings suggest that macrophage cytocidal activity of Vgamma1+ T cells may be a universal feature of pathogen-induced immune responses and that microenvironmental factors influence the involvement and function of gammadelta T cells in the host response to infection.

Host and virus determinants of picornavirus pathogenesis and tropism

The family Picornaviridae contains some notable members, including rhinovirus, which infects humans more frequently than any other virus; poliovirus, which has paralysed or killed millions over the years; and foot-and-mouth-disease virus, which led to the creation of dedicated institutes throughout the world. Despite their profound impact on human and animal health, the factors that regulate pathogenesis and tissue tropism are poorly understood. In this article, we review the clinical and economic challenges that these agents pose, summarize current knowledge of host-pathogen interactions and highlight a few of the many outstanding questions that remain to be answered.

Delineation of the function of a major gamma delta T cell subset during infection

Gammadelta T cells play important but poorly defined roles in pathogen-induced immune responses and in preventing chronic inflammation and pathology. A major obstacle to defining their function is establishing the degree of functional redundancy and heterogeneity among gammadelta T cells. Using mice deficient in Vgamma1+ T cells which are a major component of the gammadelta T cell response to microbial infection, a specific immunoregulatory role for Vgamma1+ T cells in macrophage and gammadelta T cell homeostasis during infection has been established. By contrast, Vgamma1+ T cells play no significant role in pathogen containment or eradication and cannot protect mice from immune-mediated pathology. Pathogen-elicited Vgamma1+ T cells also display different functional characteristics at different stages of the host response to infection that involves unique and different populations of Vgamma1+ T cells. These findings, therefore, identify distinct and nonoverlapping roles for gammadelta T cell subsets in infection and establish the complexity and adaptability of a single population of gammadelta T cells in the host response to infection that is not predetermined, but is, instead, shaped by environmental factors.

Type 1 immunity provides both optimal mucosal and systemic protection against a mucosally invasive, intracellular pathogen

It has been hypothesized that optimal vaccine immunity against mucosally invasive, intracellular pathogens may require the induction of different types of immune responses in mucosal and systemic lymphoid tissues. Mucosal type 2/3 responses (producing interleukin-4 [IL-4], IL-6 and/or transforming growth factor beta) could be necessary for optimal induction of protective secretory immunoglobulin A responses. On the other hand, systemic type 1 responses (including gamma interferon [IFN-gamma], tumor necrosis factor alpha, and optimal cytotoxic T-cell responses) are likely to be critical for protection against the disseminated intracellular replication that occurs after mucosal invasion. Despite these predictions, we recently found that vaccines inducing highly polarized type 1 immunity in both mucosal and systemic tissues provided optimal mucosal and systemic protection against the protozoan pathogen Trypanosoma cruzi. To further address this important question in a second model system, we now have studied the capacity of knockout mice to develop protective immune memory. T. cruzi infection followed by nifurtimox treatment rescue was used to immunize CD4, CD8, beta2-microglobulin, inducible nitric oxide synthase (iNOS), IL-12, IFN-gamma, and IL-4 knockout mice. Despite the previously demonstrated importance of CD4(+) T cells, CD8(+) T cells, and nitric oxide for T. cruzi immunity, CD4, CD8, and iNOS knockout mice developed mucosal and systemic protective immunity. However, IL-12, IFN-gamma, and beta2-microglobulin-deficient mice failed to develop mucosal or systemic protection. In contrast, IL-4 knockout mice developed maximal levels of both mucosal and systemic immune protection. These results strongly confirm our earlier conclusion from studies with polarizing vaccination protocols that type 1 immunity provides optimal mucosal and systemic protection against a mucosally invasive, intracellular pathogen.

Roles of tumor necrosis factor alpha (TNF-alpha) and the p55 TNF receptor in CD1d induction and coxsackievirus B3-induced myocarditis

Giving C57BL/6 mice 10(4) PFU of coxsackievirus B3 (H3 variant) fails to induce myocarditis, but increasing the initial virus inoculum to 10(5) or 10(6) PFU causes significant cardiac disease. Virus titers in the heart were equivalent at days 3 and 7 in mice given all three virus doses, but day 3 titers in the pancreases of mice inoculated with 10(4) PFU were reduced. Tumor necrosis factor alpha (TNF-alpha) concentrations in the heart were increased in all infected mice, but cytokine levels were highest in mice given the larger virus inocula. TNF-alpha(-/-) and p55 TNF receptor-negative (TNFR(-/-)) mice developed minimal myocarditis compared to B6;129 or C57BL/6 control mice. p75 TNFR(-/-) mice were as disease susceptible as C57BL/6 animals. No significant differences in virus titers in heart or pancreas were observed between the groups, but C57BL/6 and p75 TNFR(-/-) animals showed 10-fold more inflammatory cells in the heart than p55 TNFR(-/-) mice, and the cell population was comprised of high concentrations of CD4(+) gamma interferon-positive and Vgamma4(+) cells. Cardiac endothelial cells isolated from C57BL/6 and p75 TNFR(-/-) mice upregulate CD1d, the molecule recognized by Vgamma4(+) cells, but infection of TNF(-/-) or p55 TNFR(-/-) endothelial cells failed to upregulate CD1d. Infection of C57BL/6 endothelial cells with a nonmyocarditic coxsackievirus B3 variant, H310A1, which is a poor inducer of TNF-alpha, failed to elicit CD1d expression, but TNF-alpha treatment of H310A1-infected endothelial cells increased CD1d levels to those seen in H3-infected cells. TNF-alpha treatment of uninfected endothelial cells had only a modest effect on CD1d expression, suggesting that optimal CD1d upregulation requires both infection and TNF-alpha signaling.