Immunoregulatory effects of α-GalCer in a murine model of autoimmune myocarditis

Treatment with alpha-galactosylceramide protects mice from early onset of nonalcoholic steatohepatitis: Role of intestinal barrier function

SCOPE

The role of invariant natural killer T cells in the development of nonalcoholic steatohepatitis (NASH) has not yet been fully understood. Here, the effect of the invariant natural killer T-cell activator alpha-galactosylceramide (αGalCer) on the development of nonalcoholic fatty liver disease and intestinal barrier function was assessed in a mouse model of early Western-style diet (WSD) induced NASH.

METHODS AND RESULTS

Female C57BL/6J mice were either fed a liquid control diet or a liquid fructose-enriched WSD for 6 wk while being treated three times weekly with αGalCer (2 μg intraperitoneal) or vehicle. Indices of liver damage, glucose metabolism, and intestinal permeability were measured. Treatment with αGalCer markedly suppressed hepatic fat accumulation and inflammation while not affecting fasting glucose. The protective effects of αGalCer were associated with a protection against the increased translocation of bacterial endotoxins and the decreased protein levels of tight junction proteins occludin and zonula occludens 1 found in vehicle-treated mice while being fed a WSD.

CONCLUSION

Taken together, our data suggest that the protective effects of αGalCer against the development of a diet-induced NASH in mice are associated with a protection against the increased translocation of intestinal bacterial endotoxins associated with the development of NASH.

Intricacies of cardiac damage in coxsackievirus B3 infection: implications for therapy

Heart disease is the leading cause of death in humans, and myocarditis is one predominant cause of heart failure in young adults. Patients affected with myocarditis can develop dilated cardiomyopathy (DCM), a common reason for heart transplantation, which to date is the only viable option for combatting DCM. Myocarditis/DCM patients show antibodies to coxsackievirus B (CVB)3 and cardiac antigens, suggesting a role for CVB-mediated autoimmunity in the disease pathogenesis; however, a direct causal link remains to be determined clinically. Experimentally, myocarditis can be induced in susceptible strains of mice using the human isolates of CVB3, and the disease pathogenesis of postinfectious myocarditis resembles that of human disease, making the observations made in animals relevant to humans. In this review, we discuss the complex nature of CVB3-induced myocarditis as it relates to the damage caused by both the virus and the host's response to infection. Based on recent data we obtained in the mouse model of CVB3 infection, we provide evidence to suggest that CVB3 infection accompanies the generation of cardiac myosin-specific CD4 T cells that can transfer the disease to naïve recipients. The therapeutic implications of these observations are also discussed.

Autoimmunity in viral myocarditis

PURPOSE OF REVIEW

To review how autoimmunity is induced in viral myocarditis.

RECENT FINDINGS

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

SUMMARY

Antigenic mimicry between microbes and cardiac proteins causes autoimmunity in myocarditis. Characteristics of innate immunity associated with cardiac infection determine relevant epitope expression (cryptic epitopes).

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.

Susceptibility to autoimmune myocarditis is associated with intrinsic differences in CD4(+) T cells

A.SW and B10.S mice share the same major histocompatibility complex (MHC) haplotype (H-2(s)). However, A.SW mice are susceptible to experimental autoimmune myocarditis (EAM) and develop severe disease after immunization with myosin, whereas B10.S mice are resistant. We found that naive A.SW mice have intrinsically increased total CD4(+) T cell counts and increased proportions of CD4(+) T cells in their spleens compared to B10.S mice. Among total CD4(+) T cells, naive A.SW mice have a lower relative frequency of forkhead box protein 3 (FoxP3(+))CD25(+) regulatory T cells (T(regs)). A.SW mice also had a higher proportion of CD4(+) T cells and a lower proportion of T(regs) in their hearts and spleen during EAM, with greater T cell activation and proliferation, compared to B10.S mice. These differences in the T cell compartment were not antigen-specific, as ovalbumin/complete Freund's adjuvant (OVA/CFA) or CFA immunization elicited the same differences in CD4(+) T cells and T(regs) between A.SW and B10.S mice. Moreover, A.SW mice had more T helper type 17 (Th17) cells and B10.S had more Th1 cells in their hearts. The higher percentage of CD4(+) T cells and their enhanced potential to differentiate towards the Th17 pathway was also observed in naive A.SW mice. Interleukin (IL)-6 is required for Th17 induction. Interestingly, IL-6Rα expression was greater on naive A.SW CD4(+) T cells, compared to B10.S CD4(+) T cells, indicating that this intrinsic difference, together with a relatively lower T(reg) proportion of CD4(+) T cells, might lead to heightened Th17 responses and greater susceptibility to autoimmunity in A.SW mice.