BackgroundMen are at an increased risk of dying from heart failure caused by inflammatory heart diseases such as atherosclerosis, myocarditis and dilated cardiomyopathy (DCM). We previously showed that macrophages in the spleen are phenotypically distinct in male compared to female mice at 12 h after infection. This innate immune profile mirrors and predicts the cardiac immune response during acute myocarditis.MethodsIn order to study sex differences in the innate immune response, five male and female BALB/c mice were infected intraperitoneally with coxsackievirus B3 (CVB3) or phosphate buffered saline and their spleens were harvested 12 h later for microarray analysis. Gene expression was determined using an Affymetrix Mouse Gene 1.0 ST Array. Significant gene changes were verified by quantitative real-time polymerase chain reaction or ELISA.ResultsDuring the innate immune response to CVB3 infection, infected males had higher splenic expression of genes which are important in regulating the influx of cholesterol into macrophages, such as phospholipase A2 (PLA2) and the macrophage scavenger receptor compared to the infected females. We also observed a higher expression in infected males compared to infected females of squalene synthase, an enzyme used to generate cholesterol within cells, and Cyp2e1, an enzyme important in metabolizing cholesterol and steroids. Infected males also had decreased levels of the translocator protein 18 kDa (TSPO), which binds PLA2 and is the rate-limiting step for steroidogenesis, as well as decreased expression of the androgen receptor (AR), which indicates receptor activation. Gene differences were not due to increased viral replication, which was unaltered between sexes.ConclusionsWe found that, compared to females, male mice had a greater splenic expression of genes which are important for cholesterol metabolism and activation of the AR at 12 h after infection. Activation of the AR has been linked to increased cardiac hypertrophy, atherosclerosis, myocarditis/DCM and heart failure in male mice and humans.

Recent findings indicate that TLR3 polymorphisms increase susceptibility to enteroviral myocarditis and inflammatory dilated cardiomyopathy (iDCM) in patients. TLR3 signaling has been found to inhibit coxsackievirus B3 (CVB3) replication and acute myocarditis in mouse models, but its role in the progression from myocarditis to iDCM has not been previously investigated. In this study we found that TLR3 deficiency increased acute ( P = 5.9 × 10−9) and chronic ( P = 6.0 × 10−7) myocarditis compared with WT B6.129, a mouse strain that is resistant to chronic myocarditis and iDCM. Using left ventricular in vivo hemodynamic assessment, we found that TLR3-deficient mice developed progressively worse chronic cardiomyopathy. TLR3 deficiency significantly increased viral replication in the heart during acute myocarditis from day 3 through day 12 after infection, but infectious virus was not detected in the heart during chronic disease. TLR3 deficiency increased cytokines associated with a T helper (Th)2 response, including IL-4 ( P = 0.03), IL-10 ( P = 0.008), IL-13 ( P = 0.002), and TGF-β1 ( P = 0.005), and induced a shift to an immunoregulatory phenotype in the heart. However, IL-4-deficient mice had improved heart function during acute CVB3 myocarditis by echocardiography and in vivo hemodynamic assessment compared with wild-type mice, indicating that IL-4 impairs cardiac function during myocarditis. IL-4 deficiency increased regulatory T-cell and macrophage populations, including FoxP3+ T cells ( P = 0.005) and Tim-3+ macrophages ( P = 0.004). Thus, TLR3 prevents the progression from myocarditis to iDCM following CVB3 infection by reducing acute viral replication and IL-4 levels in the heart.

Recent studies have shown that innate immunity influences the progression from viral infection to autoimmunity. The incidence and severity of autoimmune disease differs between men and women, including the heart inflammatory autoimmune disease myocarditis which is increased in men. To better understand the reason for increased heart disease in men, we studied sex differences in the innate immune response to heart-passaged coxsackievirus B3 (CVB3) in BALB/c mice by microarray. Five male and female BALB/c mice were infected intraperitoneally (ip) with CVB3 and spleens harvested 12 hours (h) later during the innate immune response and compared to uninfected controls. Gene expression was determined using an Affymetrix Mouse Gene 1.0 ST Array. We found that 24 genes were significantly increased in CVB3 infected males vs. females (>1.5 fold change). Androgen receptor (AR) mRNA was significantly decreased in infected males vs. infected females indicating activation of the receptor. Heat shock protein 90 (HSP90) and haptoglobin (Hp) mRNA were significantly increased in infected males vs. infected females. AR, HSP90 and Hp have been associated with increased heart disease in men. Significant gene changes were verified using qRT-PCR. Thus, we found that several genes important for the development of clinical heart disease are upregulated in males during the innate immune response. Funded in part by the Johns Hopkins University Diversity Summer Internship Program and NIH R01 HL087033.