Vgamma4(+) T cells promote autoimmune CD8(+) cytolytic T-lymphocyte activation in coxsackievirus B3-induced myocarditis in mice: role for CD4(+) Th1 cells

Remission of CVB3-induced viral myocarditis by in vivo Th2 polarization via hydrodynamics-based interleukin-4 gene transfer

BACKGROUND

Regulation of Th polarization was critical for the prevention of Coxsackievirus B3 (CVB3) induced myocarditis. In the present study, interleukin (IL)-4 was over-expressed by hydrodynamics-based gene transfection (HGT) to induce the in vivo Th2 bias and evaluate the influence of Th polarization on the pathogenesis of CVB3-myocaditis.

METHODS

IL-4 expressing plasmid was delivered into BALB/c mice by HGT after CVB3 infection. In vivo Th polarization was evaluated by detecting expression of Th1/Th2 cytokine, antibody isotype and Th related transcription factor, as well as the proliferation of CD8(+) T cells. The severity of myocarditis was assessed by weight loss, serological index of myocarditis, pathological feature, as well as survival rate.

RESULTS

HGT of IL-4 plasmid resulted in high-level and long-lasting expression of IL-4 in different organs, which rescued mice from severe heart inflammation and death. This may due to the induction of a Th2-bised immune response specified with decreased expression of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma but increased expression of IL-10 and IL-4 in serum and heart tissue, more IL-4 but less IFN-gamma secreting splenic CD4+ T cells, an immunoglobulin G1 isotype switch, increased expression of GATA-3 and low proliferation of CD8+ T cells, without significant change of virus titer in heart tissue.

CONCLUSIONS

CVB3-induced myocarditis could be remitted through in vivo Th2 polarization, which has implications for our understanding of the role of Th2 population in immunity to CVB3 infection and for the development of new therapies for CVB3-myocarditis.

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.

Role of two distinct gammadelta T cell subsets during West Nile virus infection

gammadelta T cells respond rapidly following West Nile virus (WNV) infection, limiting viremia and invasion of the central nervous system and thereby protecting the host from lethal encephalitis. Here, we investigated the role of two major subpopulations of peripheral gammadelta T cells, Vgamma1(+) and Vgamma4(+) cells, in host immunity against WNV infection. We found initially that aged mice were more susceptible to WNV infection than young mice. Following WNV challenge, Vgamma1(+) cells in young mice expanded significantly whereas Vgamma4(+) cells expanded modestly. In contrast, aged mice exhibited a slower and reduced response of Vgamma1(+) cells but maintained a higher content of Vgamma4(+) cells. Vgamma1(+) cells were the major gammadelta subset producing IFN-gamma during WNV infection. Mice depleted of Vgamma1(+) cells had an enhanced viremia and higher mortality to WNV encephalitis. Vgamma4(+) cells had a higher potential for producing tumor necrosis factor-alpha (TNF-alpha), a cytokine known to be involved in blood-brain barrier compromise and WNV entry into the brain. Depletion of Vgamma4(+) cells reduced TNF-alpha level in the periphery, accompanied by a decreased viral load in the brain and a lower mortality to WN encephalitis. These results suggest that Vgamma1(+) and Vgamma4(+) cells play distinct roles in protection and pathogenesis during WNV infection.

Blood dendritic cell levels and phenotypic characteristics in relation to etiology of end-stage heart failure: implications for dilated cardiomyopathy

BACKGROUND

Dysregulation of dendritic cell (DC) mediated immune responses towards auto-antigens, is considered an important feature in the maintenance of experimentally induced heart failure (HF). In order to evaluate the role of blood DCs in cardiomyopathies of different origins, we examined myeloid (mDC) and plasmacytoid (pDC) subset levels and maturation characteristics, according to HF severity and etiology in humans.

METHODS

Absolute numbers of mDCs and pDCs in 12 New York Heart Association (NYHA) class-II, 28 NYHA class III-IV HF patients and 18 healthy controls, were studied by 4-colour whole blood flow cytometry.

RESULTS

End-stage (NYHA III-IV) HF patients had comparable circulating DC subset levels to NYHA-II patients and controls. However, within the NYHA III-IV group total DC levels in patients with non-ischemic dilated cardiomyopathy (DCM) were higher (P<0.001) than in patients with coronary artery disease (CAD), hypertrophic cardiomyopathy (HCM) or other HF etiology. This was due to a significant increase of primarily mDCs (P<0.0001) and to a lesser extent of pDCs (P<0.05) in idiopathic DCM patients, independent of systolic or diastolic cardiac dysfunction. Maturation marker CD83 and lymphoid homing chemokine receptor CCR7 surface expression was enhanced only on mDCs, but not pDCs from DCM patients (P<0.05), compared to patients with CAD, HCM or other underlying cardiac pathophysiology.

CONCLUSIONS

Total blood DC levels in end-stage HF are elevated in patients with DCM. Whole blood DC characterisation may lead to new insights into the pathophysiology of idiopathic DCM in humans.

IFN-gamma production dominates the early human natural killer cell response to Coxsackievirus infection

Coxsackieviruses (CV) are important human pathogens that have been implicated in the pathogenesis of several diseases, including myocarditis and pancreatitis. How the human immune system recognizes and controls CV infections is not well understood. Studies in mice suggest that natural killer (NK) cells play a critical role in viral clearance and host survival, but the mechanism(s) by which human NK cells may contribute to the host anti-CV defence has not been investigated. Here we show that CVB3 infection markedly reduces HLA class I cell surface expression but does not increase the expression of the activating NK cell receptor ligands MICA/B and ULBP1-3 on human cells. We also demonstrate that the lowered target cell HLA class I surface expression does not correlate with an increased susceptibility to NK cell-mediated killing. However, NK cells responded with a robust production of interferon gamma (IFN-gamma) when peripheral blood mononuclear cells were cocultured with infected cells. In summary, this study shows that CVB3 interferes with the expression of NK cell receptor ligands on infected cells and indicates that IFN-gamma production, rather than cytotoxicity, marks the early human NK cell response to CVB3 infection.

Induction of IL-13 triggers TGF-beta1-dependent tissue fibrosis in chronic 2,4,6-trinitrobenzene sulfonic acid colitis

To investigate the immunopathogenesis of inflammation-associated fibrosis, we analyzed the chronic colitis and late-developing fibrosis occurring in BALB/c mice administered weekly doses of intrarectal 2,4,6-trinitrobenzene sulfonic acid. We showed first in this model that an initial Th1 response involving IL-12p70 and IFN-gamma subsides after 3 wk to be supplanted by an IL-23/IL-25 response beginning after 4-5 wk. This evolution is followed by gradually increasing production of IL-17 and cytokines ordinarily seen in a Th2 response, particularly IL-13, which reaches a plateau at 8-9 wk. In vitro stimulation studies suggest that this IL-13 production is dependent on IL-23 and IL-25, but not on IL-12p70. We then show that IL-13 production results in the induction of an IL-13R formerly thought to function only as a decoy receptor, IL-13Ralpha(2), and this receptor is critical to the production of TGF-beta(1) and the onset of fibrosis. Thus, if IL-13 signaling through this receptor is blocked by administration of soluble IL-13Ralpha(2)-Fc, or by administration of IL-13Ralpha(2)-specific small interfering RNA, TGF-beta(1) is not produced and fibrosis does not occur. These studies show that in chronic 2,4,6-trinitrobenzene sulfonic acid colitis, fibrosis is dependent on the development of an IL-13 response that acts through a novel cell surface-expressed IL-13R to induce TGF-beta(1). A similar mechanism may obtain in certain forms of human inflammatory bowel disease.

TLR ligands act directly upon T cells to restore proliferation in the absence of protein kinase C-theta signaling and promote autoimmune myocarditis

The serine/threonine kinase, protein kinase C-theta (PKC-theta), plays a central role in the activation and differentiation of Th2 cells while being redundant in CD4+ and CD8+ antiviral responses. Recent evidence indicates that PKC-theta may however be required for some T cell-driven autoimmune responses. We have investigated the role of PKC-theta in the induction of autoimmune myocarditis induced by either Coxsackie B3 virus infection or immunization with alpha-myosin/CFA (experimental autoimmune myocarditis (EAM)). PKC-theta-deficient mice did not develop EAM as shown by impaired inflammatory cell infiltration into the heart, reduced CD4+ T cell IL-17 production, and the absence of a myosin-specific Ab response. Comparatively, PKC-theta was not essential for both early and late-phase Coxsackie virus-induced myocarditis. We sought to find alternate pathways of immune stimulation that might reconcile the differential requirements for PKC-theta in these two disease models. We found systemic administration of the TLR ligand CpG restored EAM in PKC-theta-deficient mice. CpG could act directly upon TLR9-expressing T cells to restore proliferation and up-regulation of Bcl-x(L), but exogenous IL-6 and TGF-beta was required for Th17 cell differentiation. Taken together, these results indicate that TLR-mediated activation of T cells can directly overcome the requirement for PKC-theta signaling and, combined with the dendritic cell-derived cytokine milieu, can promote the development of autoimmunity.

Early inflammatory responses direct chronic autoimmunity development in the heart following coxsackievirus infection

Coxsackievirus infections are a major cause of chronic autoimmune myocarditis, a known precursor to dilated cardiomyopathy. Dilated cardiomyopathy leads to heart failure and is responsible for nearly half of all heart transplant cases. The induction of chronic autoimmunity following coxsackievirus infection is governed by the interplay of several genetic and immunological factors. In this review, we will focus on how the innate immune response to viral infection directs a cascade of events that ultimately results in chronic autoimmune heart disease.

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.

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.

Sex differences in coxsackievirus B3-induced myocarditis: IL-12Rbeta1 signaling and IFN-gamma increase inflammation in males independent from STAT4

Cardiovascular disease is the number one killer of men and women in North America. Male BALB/c mice infected with coxsackievirus B3 (CVB3) develop more severe inflammatory heart disease compared to female mice, similar to the increased heart disease that occurs in men. We show here that increased inflammation in male mice is not due to increased viral replication in the heart, but associated with increased proinflammatory cytokines IL-1beta, IL-18 and IFN-gamma. We have previously reported that IL-12Rbeta1 signaling increases CVB3-induced myocarditis and IL-1beta/IL-18 levels in males, while IL-12(p35)/STAT4-induced IFN-gamma does not alter the severity of acute disease. However, whether differences exist between males and females in these two cytokine signaling pathways is unknown. In this study, we examined sex differences in 1) IL-12Rbeta1 signaling or 2) STAT4/IFN-gamma pathways following CVB3 infection in BALB/c mice. We found that male and female mice deficient in IL-12Rbeta1 had decreased inflammation and viral replication in the heart, indicating that IL-12Rbeta1 signaling increases myocarditis in both sexes. In contrast, STAT4 deficiency did not alter the sex difference in myocarditis, with males maintaining increased inflammation over females. IFN-gamma deficient males, however, had decreased myocarditis and viral replication compared to females. Thus, IFN-gamma increases inflammation in males independent from STAT4. These results demonstrate that sex differences greatly influence viral replication and the severity of acute CVB3-induced myocarditis.

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.

Molecular mimicry, bystander activation, or viral persistence: infections and autoimmune disease

Virus infections and autoimmune disease have long been linked. These infections often precede the occurrence of inflammation in the target organ. Several mechanisms often used to explain the association of autoimmunity and virus infection are molecular mimicry, bystander activation (with or without epitope spreading), and viral persistence. These mechanisms have been used separately or in various combinations to account for the immunopathology observed at the site of infection and/or sites of autoimmune disease, such as the brain, heart, and pancreas. These mechanisms are discussed in the context of multiple sclerosis, myocarditis, and diabetes, three immune-medicated diseases often linked with virus infections.

PROTECTING THE PUMP: Controlling Myocardial Inflammatory Responses

Because of the anatomy, function, and nonregenerative nature of the myocardium, inflammation in this tissue is not well tolerated. Nevertheless, various diseases of the heart are characterized by inflammatory responses involving the effector mechanisms of innate and adaptive (lymphocyte-dependent) immunity. The innate immune response to ischemia-reperfusion injury is, by far, the most common cause of myocardial inflammation. Innate responses may have beneficial influences that preserve myocardial function in the short term but may be maladaptive in chronic states. Adaptive responses in the myocardium occur with infection or loss of tolerance, and lead to myocarditis. Given the narrow margin for benefit of cardiac inflammation, special regulatory mechanisms likely raise the threshold, compared to other tissues, for the induction and persistence of adaptive immune responses. These mechanisms include strong central and peripheral T cell tolerance to heart antigens and induction of anti-inflammatory feedback mechanisms involving cytokines such as interferon-gamma.

Myocarditis, microbes and autoimmunity

Acute and chronic myocarditis can be caused by a number of infectious agents, including viruses, bacteria and protozoa. These diseases are refractory to treatment, and the development of rational therapies will require a detailed understanding of the mechanisms that underlie the pathological inflammatory responses. Here, we review three infectious myocarditides that, despite the dissimilarity of the microorganisms, share several common features: (i) the microbes replicate in the heart; but (ii) are difficult to isolate, in infectious form, during chronic disease; (iii) autoreactive antibodies and T cells specific for cardiac antigens have been identified in infected animals; and (iv) these autoreactive responses have been proposed as the main effectors of cell death, and myocardial damage. We critically evaluate the data, and we suggest that the findings can be reconciled without invoking autoimmunity as an effector mechanism. Alternative hypotheses to explain the tissue destruction are proposed.

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.

Antiviral reactivities of gammadelta T cells

The complex antiviral immune mechanisms involve both adaptive and innate reactions mediated by γδ T lymphocytes, whose unique immunosurveillance contributions are analyzed here in different clinical and experimental settings. It is beyond any doubt that the fast, potent, cytotoxic as well as non-cytolytic antiviral activities of γδ T cells are critical in protecting the host against diverse viral pathogens.

Autoimmune heart failure: new understandings of pathogenesis

Besides genetic susceptibility and infections with cardiotropic viruses, autoimmune responses against heart tissue play a major role in the pathogenesis of dilated cardiomyopathy, the most common cause of heart failure in young patients. Recent findings suggest that the combination of tissue damage resulting in release of self-antigens, together with non-specific activation of the innate immune system triggers various responses that are crucial for the development of heart-specific autoimmunity. Understanding these mechanisms is critical for the design and development of novel treatment strategies against devastating heart diseases in the future.

Dual functions of murine gammadelta cells in inflammation and autoimmunity in coxsackievirus B3-induced myocarditis: role of Vgamma1+ and Vgamma4+ cells

Coxsackieviruses are a cause of clinical myocarditis. Both virus replication and host defense mechanisms, including virus-induced autoimmunity, mediate heart injury and cardiac dysfunction. Vgamma4+ cells kill infected cardiocytes and virus-specific CD4+ Th2 cells through Fas-dependent apoptosis and CD1d. The CD4+ Th1 response is necessary for activation of the autoimmune CD8+ T cells, which kill uninfected cardiocytes through perforin-dependent mechanisms.

Critical proinflammatory and anti-inflammatory functions of different subsets of CD1d-restricted natural killer T cells during Trypanosoma cruzi infection

Trypanosoma cruzi infects 15 to 20 million people in Latin America and causes Chagas disease, a chronic inflammatory disease with fatal cardiac and gastrointestinal sequelae. How the immune response causes Chagas disease is not clear, but during the persistent infection both proinflammatory and anti-inflammatory responses are critical. Natural killer T (NKT) cells have been shown to regulate immune responses during infections and autoimmune diseases. We report here that during acute T. cruzi infection NKT-cell subsets provide distinct functions. CD1d(-/-) mice, which lack both invariant NKT (iNKT) cells and variant NKT (vNKT) cells, develop a mild phenotype displaying an increase in spleen and liver mononuclear cells, anti-T. cruzi antibody response, and muscle inflammation. In contrast, Jalpha18(-/-) mice, which lack iNKT cells but have vNKT cells, develop a robust phenotype involving prominent spleen, liver, and skeletal muscle inflammatory infiltrates comprised of NK, dendritic, B and T cells. The inflammatory cells display activation markers; produce more gamma interferon, tumor necrosis factor alpha, and nitric oxide; and show a diminished antibody response. Strikingly, most Jalpha18(-/-) mice die. Thus, in response to the same infection, vNKT cells appear to augment a robust proinflammatory response, whereas the iNKT cells dampen this response, possibly by regulating vNKT cells.

IL-12 Protects against Coxsackievirus B3-Induced Myocarditis by Increasing IFN-γ and Macrophage and Neutrophil Populations in the Heart

Th1-type immune responses, mediated by IL-12-induced IFN-gamma, are believed to exacerbate certain autoimmune diseases. We recently found that signaling via IL-12Rbeta1 increases coxsackievirus B3 (CVB3)-induced myocarditis. In this study, we examined the role of IL-12 on the development of CVB3-induced myocarditis using mice deficient in IL-12p35 that lack IL-12p70. We found that IL-12 deficiency did not prevent myocarditis, but viral replication was significantly increased. Although there were no changes in the total percentage of inflammatory cells in IL-12-deficient hearts compared with wild-type BALB/c controls by FACS analysis, macrophage and neutrophil populations were decreased. This decrease corresponded to reduced TNF-alpha and IFN-gamma levels in the heart, suggesting that macrophage and/or neutrophil populations may be a primary source of TNF-alpha and IFN-gamma during acute CVB3 myocarditis. Increased viral replication in IL-12-deficient mice was not mediated by reduced TNFRp55 signaling, because viral replication was unaltered in TNFRp55-deficient mice. However, STAT4 or IFN-gamma deficiency resulted in significantly increased viral replication and significantly reduced TNF-alpha and IFN-gamma levels in the heart, similar to IL-12 deficiency, indicating that the IL-12/STAT4 pathway of IFN-gamma production is important in limiting CVB3 replication. Furthermore, STAT4 or IFN-gamma deficiency also increased chronic CVB3 myocarditis, indicating that therapeutic strategies aimed at reducing Th1-mediated autoimmune diseases may exacerbate common viral infections such as CVB3 and increase chronic inflammatory heart disease.

Coxsackievirus group B type 3 infection upregulates expression of monocyte chemoattractant protein 1 in cardiac myocytes, which leads to enhanced migration of mononuclear cells in viral myocarditis

Coxsackievirus group B type 3 (CVB3) is an important cause of viral myocarditis. The infiltration of mononuclear cells into the myocardial tissue is one of the key events in viral myocarditis. Immediately after CVB3 infects the heart, the expression of chemokine(s) by infected myocardial cells may be the first trigger for inflammatory infiltration and immune response. However, it is unknown whether CVB3 can induce the chemokine expression in cardiac myocytes. Monocyte chemoattractant protein 1 (MCP-1) is a potent chemokine that stimulates the migration of mononuclear cells. The objective of the present study was to investigate the effect of CVB3 infection on MCP-1 expression in murine cardiac myocytes and the role of MCP-1 in migration of mononuclear cells in viral myocarditis. Our results showed that the expression of MCP-1 was significantly increased in cardiac myocytes after wild-type CVB3 infection in a time- and dose-dependent manner, which resulted in enhanced migration of mononuclear cells in mice with viral myocarditis. The migration of mononuclear cells was partially abolished by antibodies specific for MCP-1 in vivo and in vitro. Administration of anti-MCP-1 antibody prevented infiltration of mononuclear cells bearing the MCP-1 receptor CCR2 in mice with viral myocarditis. Infection by UV-irradiated CVB3 induced rapid and transient expression of MCP-1 in cardiac myocytes. In conclusion, our results indicate that CVB3 infection stimulates the expression of MCP-1 in myocardial cells, which subsequently leads to migration of mononuclear cells in viral myocarditis.

T cells in coxsackievirus-induced myocarditis

Myocarditis is a complex disease in which distinct immunopathogenic mechanisms cause tissue injury. In some but not all cases, autoimmunity is a major pathogenic factor. Cross-reactivity between viral and myosin epitopes underlies both cellular and humoral autoimmunity in myocarditis. Thus, the genetics of the host as well as the virus determine disease pathogenicity. Innate immunity, as represented by gammadelta+ T cells, is important in determining disease susceptibility. The innate effectors rapidly localize in the infected myocardium and through release of IFNgamma (Vgamma4+ cells; BALB/c) or IL-4 (Vgamma1+ cells; C57Bl/6), modulate the developing adaptive immune response to either a Th1 or Th2 response, respectively. The Vgamma4+ cells in BALB/c mice recognize CD1d, a major histocompatibility complex class I-like antigen. The ligand for Vgamma1+ cells is unknown. Only infected myocytes up-regulate CD1d. Signaling through both infection (double stranded RNA) and TNFalpha is required for CD1d up-regulation.

Hepatic CD1d Expression in Hepatitis C Virus Infection and Recognition by Resident Proinflammatory CD1d-Reactive T Cells

A subset of CD161(+)CD56(+/-) NKT cells can recognize glycolipids presented by CD1d and positively or negatively regulate inflammatory responses, including those implicated in several models of hepatitis. CD1d is expressed at very low levels in the healthy liver, but there is a large fraction of CD161(+)CD56(+) NKT cells. There are high levels of nonclassical proinflammatory hepatic CD1d-reactive T cells in hepatitis C virus (HCV) infection. Hepatic inflammatory cells and biliary cells adjacent to portal tract fibrotic areas of HCV-infected donors specifically up-regulated CD1d. A hepatocyte cell line expressing minimal CD1d was efficiently recognized by hepatic CD1d-reactive T cells, suggesting a role for these cells in disease. Hepatic CD1d-reactive T cells from HCV-positive as well as negative donors produced large amounts of IFN-gamma with some IL-13, but only rarely detectable IL-4. We confirmed large numbers of hepatic CD161(+) T cells, lower levels of CD56(+) T cells, and small numbers of classic invariant NKT cells. However, hepatic CD1d-reactivity was not restricted to any of these populations. We suggest virally infected hepatic cells can process potent CD1d-presented liver Ag(s), for surveillance by resident Th1 hepatic CD1d-reactive T cells. This process may be beneficial in acute viral clearance, but in chronic infection could contribute to liver injury.

Quantitative analysis of myocardial inflammation by flow cytometry in murine autoimmune myocarditis: correlation with cardiac function

Inflammation has been increasingly recognized as an important pathological component of heart failure. Existing methods of assessing myocardial infiltrate are labor-intensive and provide data that are difficult to quantify and not representative of the whole heart. As a result, little effort has been made to systematically assess the components of myocardial inflammation. We established an alternative method of quantitative assessment of myocardial inflammation by flow cytometry after enzymatic digestion of hearts to characterize the infiltrate and study the association between inflammation and cardiac function in murine experimental autoimmune myocarditis. The severity of acute myocarditis uniquely correlated with the proportion of neutrophils, but not T cells, B cells, or macrophages. Both acute and chronic phases were characterized by the presence of CD44high (activated) T cells in the heart, whereas T cells trafficking through normal hearts exhibited CD44low phenotype. During the chronic phase, the proportion of CD4+ T cells was associated with increased left-ventricular volumes and deterioration of systolic function, the hallmarks of dilated cardiomyopathy. We conclude that flow cytometry on uniformly digested mouse hearts provides sensitive and reproducible assessment of myocardial infiltrate and can be used to dissect out the specific role of individual immune components from the overall inflammatory response in the heart.

Detection of Cell Surface Ligands for the γδ TCR Using Soluble TCRs

The natural ligands recognized by gammadelta TCRs are still largely unknown, in part because immunization does not normally result in Ag-specific gammadelta T cell responses. Taking advantage of an established ligand for a particular gammadelta TCR, we demonstrated that a multimerized recombinant form of this gammadelta TCR can be used like a mAb to specifically detect its own ligand. Using the same approach for more common gammadelta TCRs whose ligands remain unknown, we detected on certain cell lines molecules that appear to be ligands for three additional gammadelta TCRs. One of these represents the mouse Vgamma6/Vdelta1 invariant gammadelta TCR, which predominates in the female reproductive tract, the tongue, and the lung, and other tissues during inflammation. The second represents the closely related Vgamma5/Vdelta1 invariant gammadelta TCR expressed by most epidermal T cells. The third is a Vgamma1/Vdelta6.3 TCR, representative of a variable type frequently found on lymphoid gammadelta T cells. We found evidence that ligands for multiple gammadelta TCRs may be simultaneously expressed on a single cell line, and that at least some of the putative ligands are protease sensitive. This study suggests that soluble versions of gammadelta TCRs can be as tools to identify and characterize the natural ligands of gammadelta T cells.

Innate immune response to encephalomyocarditis virus infection mediated by CD1d

CD1d-reactive natural killer T (NKT) cells can rapidly produce T helper type 1 (Th1) and/or Th2 cytokines, can activate antigen-presenting cell (APC) interleukin-12 (IL-12) production, and are implicated in the regulation of adaptive immune responses. The role of the CD1d system was assessed during infection with encephalomyocarditis virus (EMCV-D), a picornavirus that causes acute diabetes, paralysis and myocarditis. EMCV-D resistance depends on IL-12-mediated interferon-gamma (IFN-gamma) production. CD1d-deficient mice, which also lack CD1d-reactive NKT cells, were substantially more sensitive to infection with EMCV-D. Infected CD1d knockout mice had decreased IL-12 levels in vitro and in vivo, and indeed were protected by treatment with exogenous IL-12. IFN-gamma production in CD1d knockout mice was decreased compared with that in wild-type (WT) mice in response to EMCV-D in vitro, although differences were not detected in vivo. Treatment with anti-asialo-GM1 antibody, to deplete NK cells, caused a marked increase in susceptibility of WT mice to EMCV-D infection, whereas CD1d knockout mice were little affected, suggesting that NK-cell-mediated protection is CD1d-dependent. Therefore, these data indicate that CD1d is essential for optimal responses to acute picornaviral infection. We propose that CD1d-reactive T cells respond to early immune signals and function in the innate immune response to a physiological viral infection by rapidly augmenting APC IL-12 production and activating NK cells.

The Interaction of γδ T Cells with Activated Macrophages Is a Property of the Vγ1 Subset

Immunoregulation is an emerging paradigm of gammadelta T cell function. The mechanisms by which gammadelta T cells mediate this function, however, are not clear. Studies have identified a direct role for gammadelta T cells in resolving the host immune response to infection, by eliminating populations of activated macrophages. The aim of this study was to identify macrophage-reactive gammadelta T cells and establish the requirements/outcomes of macrophage-gammadelta T cell interactions during the immune response to the intracellular bacterium, Listeria monocytogenes (Lm). Using a macrophage-T cell coculture system in which peritoneal macrophages from naive or Lm-infected TCRdelta(-/-) mice were incubated with splenocytes from naive and Lm-infected alphabeta/gammadelta T cell-deficient and wild-type mice, the ability to bind macrophages was shown to be restricted to gammadelta T cells and the GV5S1 (Vgamma1) subset of gammadelta T cells. Macrophage adherence resulted in a 4- to 10-fold enrichment of Vgamma1(+) T cells. Enrichment of Vgamma1 T cells was dependent upon the activation status of macrophages, but independent of the activation status of gammadelta T cells. Vgamma1 T cells were cytotoxic for activated macrophages with both the binding to and killing of macrophages being TCR dependent because anti-TCRgammadelta Abs inhibited both Vgamma1 binding and killing activities. These studies establish the identity of macrophage cytotoxic gammadelta T cells, the conditions under which this interaction occurs, and the outcome of this interaction. These findings are concordant with the involvement of Vgamma1 T cells in macrophage homeostasis during the resolution of pathogen-mediated immune responses.

IFN-gamma-producing gamma delta T cells help control murine West Nile virus infection

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, thereby partially mimicking human disease. Using this model, we have demonstrated that mice deficient in gammadelta T cells are more susceptible to WN virus infection. TCRdelta(-/-) mice have elevated viral loads and greater dissemination of the pathogen to the CNS. In wild-type mice, gammadelta T cells expanded significantly during WN virus infection, produced IFN-gamma in ex vivo assays, and enhanced perforin expression by splenic T cells. Adoptive transfer of gammadelta T cells to TCRdelta(-/-) mice reduced the susceptibility of these mice to WN virus, and this effect was primarily due to IFN-gamma-producing gammadelta T cells. These data demonstrate a distinct role for gammadelta T cells in the control of and prevention of mortality from murine WN virus infection.

Exogenous interleukin-12 protects against lethal infection with coxsackievirus B4

Infections with the group B coxsackieviruses either can be asymptomatic or can lead to debilitating chronic diseases. To elucidate the mechanism by which these viruses cause chronic disease, we developed a mouse model of chronic pancreatitis by using a virulent variant of coxsackievirus B4, CVB4-V. Infection with CVB4-V results in an early, severe pancreatitis, which can lead to mortality or progress to chronic pancreatitis. Chronic pancreatitis, in this model, is due to immunopathological mechanisms. We investigated whether interleukin-12 (IL-12) could modulate the outcome of CVB4-V infection. Eighty-five percent of the infected mice treated with 500 ng of IL-12 survived, whereas all untreated mice succumbed. To understand the mechanism underlying the beneficial effect of IL-12, we investigated the role of gamma interferon (IFN-gamma). Three lines of evidence suggest that the protective effect of IL-12 is due to IFN-gamma. First, administration of IL-12 increased the production of endogenous IFN-gamma in CVB4-V-infected mice. Both NK and NKT cells were identified as the source of IFN-gamma. Second, IFN-gamma knockout mice treated with IL-12 succumbed to infection with CVB4-V. Third, wild-type mice treated with IFN-gamma survived infection with CVB4-V. Due to the antiviral effects of IFN-gamma, we examined whether IL-12 treatment affected viral replication. Administration of IL-12 did not decrease viral replication in the pancreas, but it did prevent extensive tissue damage and the subsequent development of chronic pancreatitis. The data suggest that IL-12 treatment during CVB4-V infection is able to suppress the immunopathological mechanisms that lead to chronic disease.

T-cell effector mechanisms: gammadelta and CD1d-restricted subsets

Gammadelta T lymphocytes and CD1d-restricted natural killer T cells are classified as innate T lymphocytes, which perform effector functions that protect from malignancy and maintain tissue integrity. Innate T cells also play important regulatory roles in autoimmunity, inflammation and infection. Recent advances have established innate T cells as both effectors and regulators of disease in biological models.

Role of CD1d in coxsackievirus B3-induced myocarditis

The myocarditic (H3) variant of Coxsackievirus B3 (CVB3) causes severe myocarditis in BALB/c mice and BALB/c mice lacking the invariant J alpha 281 gene, but minimal disease in BALB/c CD1d(-/-) animals. This indicates that CD1d expression is important in this disease but does not involve the invariant NKT cell often associated with CD1d-restricted immunity. The H3 variant of the virus increases CD1d expression in vitro in neonatal cardiac myocytes whereas a nonmyocarditic (H310A1) variant does not. V gamma 4(+) T cells show increased activation in both H3-infected BALB/c and J alpha 281(-/-) mice compared with CD1d(-/-) animals. The activated BALB/c V gamma 4(+) T cells from H3-infected mice kill H3-infected BALB/c myocytes and cytotoxicity is blocked with anti-CD1d but not with anti-MHC class I (K(d)/D(d)) or class II (IA/IE) mAbs. In contrast, H3 virus-infected CD1d(-/-) myocytes are not killed. These studies demonstrate that CD1d expression is essential for pathogenicity of CVB3-induced myocarditis, that CD1d expression is increased early after infection in vivo in CD1d(+) mice infected with the myocarditic but not with the nonmyocarditic CVB3 variant, and that V gamma 4(+) T cells, which are known to promote myocarditis susceptibility, appear to recognize CD1d expressed by CVB3-infected myocytes.

Immunoregulation in the tissues by gammadelta T cells

For a T-cell subset to be classified as immunoregulatory, it might reasonably be predicted that in its absence, animals would experience pathological immune dysregulation. Moreover, reconstitution of the subset should restore normal immune regulation. So far, these criteria have been satisfied by only a few of the candidate regulatory T-cell subsets, but among them is the intraepithelial gammadelta T-cell receptor (TCR)+ subset of mouse skin. In this article, we look at immunoregulatory gammadelta T cells, and the growing evidence for tissue-associated immunoregulation mediated by both gammadelta T cells and alphabeta T cells.