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Coxsackievirus B3-induced myocarditis: perforin exacerbates disease, but plays no detectable role in virus clearance
J R Gebhard1, C M Perry, S Harkins
1Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California 92037, USA.
Insights
Perforin deficiency in mice reduces viral myocarditis severity and scarring by limiting immune pathology, while still allowing viral clearance. This suggests perforin as a therapeutic target for myocarditis.
Area of Science:
- Immunology
- Virology
- Cardiovascular Medicine
Background:
- Viral myocarditis, often caused by coxsackievirus B3, involves CD8+ cytotoxic T lymphocytes (CTLs).
- CTLs exhibit dual roles in myocarditis, controlling viral replication but also causing inflammation and myocardial scarring.
- The specific role of perforin, a key CTL protein, in coxsackievirus B (CVB) myocarditis pathogenesis remained unproven.
Purpose of the Study:
- To investigate the role of perforin in CVB-induced myocarditis using perforin knockout (PKO) mice.
- To determine if perforin is essential for viral clearance or primarily involved in immunopathology.
- To explore the potential of targeting perforin or chemokine pathways for myocarditis therapy.
Main Methods:
- Utilized perforin knockout (PKO) mice and their wild-type littermates (+/+).
- Administered lethal and non-lethal doses of coxsackievirus B (CVB) to assess survival and myocarditis severity.
- Analyzed viral load, myocarditis histology, myocardial fibrosis, apoptosis, and chemokine expression (e.g., MIP-1alpha).
Main Results:
- PKO mice exhibited significantly higher survival rates and milder myocarditis compared to perforin+ mice after CVB infection.
- Perforin deficiency led to reduced myocardial lesions and minimal fibrosis, whereas perforin+ mice developed severe scarring.
- Viral clearance and replication kinetics were comparable between PKO and perforin+ mice, indicating perforin is not crucial for viral control.
- Chemokine expression, particularly MIP-1alpha, was reduced in PKO mice, correlating with diminished myocarditis severity.
Conclusions:
- Perforin plays a critical role in the immunopathology of CVB myocarditis, contributing to myocardial damage and fibrosis.
- Ablating perforin function effectively uncouples the immunopathological and antiviral effects of CTLs, offering a therapeutic strategy.
- Targeting perforin or chemokine pathways presents a promising approach to mitigate myocarditis and its long-term consequences while preserving viral clearance.
Abstract:
Viral myocarditis is remarkably common, being detected in approximately 1% of unselected asymptomatic individuals. Many cases are attributable to enteroviral infection, and in particular to coxsackievirus B3. The underlying pathogenesis is controversial, but most studies admit the important immunopathological role of infiltrating CD8+ (cytotoxic) T lymphocytes (CTLs). We have previously shown that CTLs play conflicting roles in coxsackievirus B (CVB) myocarditis; they assist in controlling virus replication, but also are instrumental in causing the extensive inflammatory disease, which often results in severe myocardial scarring. A role for perforin, the major CTL cytolytic protein, in CVB myocarditis has been suggested, but never proven. In the present study we use perforin knockout (PKO) mice to show that perforin plays a major role in CVB infection; in broad terms, perforin is important in immunopathology, but not in CVB clearance. For example, PKO mice are better able to withstand a normally lethal dose of CVB (100% survival of PKO mice compared with 90% death in +/+ littermates). In addition, PKO mice given a nonlethal dose of CVB develop only a mild myocarditis, whereas their perforin+ littermates have extensive myocardial lesions. The myocarditis in PKO mice resolves more quickly, and these mice show minimal histological sequelae; in contrast, late in disease the perforin+ mice develop severe myocardial fibrosis. PKO mice, despite lacking this major CTL effector function, can control the infection and eradicate the virus; growth kinetics and peak CVB titers are indistinguishable in PKO and perforin+ mice. Therefore, the immunopathological and antiviral effects of CTLs can be uncoupled by ablation of perforin; this offers a promising target for therapy of myocarditis. Furthermore, we evaluate the possible roles of apoptosis, and of chemokine expression, in CVB infection. In perforin+ mice, apoptotic cells are detected within the inflammatory infiltrate, whereas in their PKO counterparts, apoptotic myocyte nuclei are seen. Chemokine expression in both PKO and perforin+ mice precedes and parallels the course of myocarditis. Several chemokines are detectable earlier in PKO mice than in perforin+ mice, but PKO mice show reduced peak levels, and chemokine expression decays sooner. In particular, MIP-1alpha expression is barely detectable at any time point in PKO mice, but it is readily identified in perforin+ animals, peaking just before the time of maximal myocarditis; this is particularly interesting, given that MIP-1alpha knockout mice are resistant to CVB myocarditis, but remain able to control viral infection. Thus, the chemokine pathway offers a second route of intervention to diminish myocarditis and its sequelae, while permitting the host to eradicate the virus.