Myocarditis is an inflammation of the heart which usually follows microbial infections. Men are more likely to develop myocarditis than women. The reasons for the gender bias in this disease are not completely clear, however, we have shown that young cycling women show natural fluctuations in expression of decay accelerating factor (DAF; CD55) which is a known receptor for coxsackieviruses. Furthermore, B lymphocytes are more susceptible to coxsackievirus infection when DAF expression is highest in the luteal phase of the ovarian cycle. We have established a murine model of coxsackievirus B3 (CVB3) induced myocarditis. Male mice are highly susceptible to inflammatory heart disease. Female mice in estrus and metestrus phases of the ovarian cycle are highly resistant, but females in diestrus and proestrus phases are suscceptible to the disease. Virus titers in the pancreas 24 hours after infection correlate to myocarditis susceptibility. Published studies have shown that only CVB3 variants which rapidly infect and replicate to high titers in the pancreas are able to induce myocarditis. We hypothesize that this early pancreatic infection elevates circulating TNFa levels which up-regulate DAF in the heart and promote cardiac infection. Estrogen suppresses systemic tumor necrosis factor-alpha (TNFa) responses which may explain the reduced pathogenicity of CVB3 in this sex. We have also shown that TNFa up-regulates expression of CD1d, a major histocompatibility complex class l-like molecule involved in innate immunity. CD1d is required for activation of T cells expressing the Vy4+ T cell receptor. vy4+ cells infiltrate the hearts of CVB3 infected male but not female mice and are required for pathogenicity. Increased circulating TNFa or cytokine produced in the heart after augmented virus infection (due to enhanced DAF expression) may be responsible for the increased CD1d levels.
The Specific Aims of this proposal are to: 1) determine the ability of heart-specific TNFa to promote myocarditis in infected female mice; and the relationship to CD1d expression in the heart; and 2) evaluate the role of DAF in myocarditis and hormonal influence on DAF expression and infection. By understanding the factors controlling virus infection and induction of innate immunity, better mechanism for controlling viral disease should be possible.
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