心肌肌钙蛋白T在病毒性心肌炎心肌组织中的表达及意义

目的:了解病毒性心肌炎心肌组织中肌钙蛋白T的表达情况,探讨病毒性心肌炎时心肌结构蛋白损伤的机制及意义。方法:运用免疫组化和计算机图像分析技术,观察13例明确性病毒性心肌炎和17例界限性病毒性心肌炎尸检心脏标本中心肌肌钙蛋白T的表达与分布。结果:在正常对照的心肌组织中,蛋白成强阳性表达,分布均匀,未见缺染。在明确性心肌炎及14例界限性心肌炎心肌组织中都存在着不同程度的蛋白表达缺染或脱失。缺染的范围及分布与病毒性心肌炎病变特点基本一致,但其范围往往小于炎症细胞浸润范围。计算机图像分析和数据统计结果显示缺染区域的心肌肌钙蛋白T表达量要明显小于其周边区域和正常心肌细胞(P＜0．01)。结论:病毒性心肌炎患者的心肌损害要早于炎症细胞的浸润,病毒的作用可能是心肌肌钙蛋白T脱失的主要因素。心肌肌钙蛋白T的免疫组化检查可以作为一种有效的手段,来辅助病毒性心肌炎的病理学诊断。     

三七总黄酮通过miR-223-3p/FOXO1分子轴缓解病毒性心肌炎炎症反应和细胞损伤

病毒性心肌炎严重影响患者身体健康,中药材中黄酮类物质被证实对病毒性心肌炎有治疗作用,但其中三七总黄酮对柯萨奇B3病毒导致的心肌炎发挥治疗作用的分子机制尚不明确.以探讨三七总黄酮缓解病毒性心肌炎炎症反应及细胞损伤的作用机制.采用RT-qPCR检测心肌细胞中miR-223-3p的表达水平;Western blotting检测心肌细胞中转录因子叉头框蛋白O1(Forkhead box O1,FOXO1)蛋白表达水平;MTT实验检测心肌细胞存活率;流式细胞术检测心肌细胞凋亡率;ELISA检测炎症因子肿瘤坏死因子-α(Tumor necrosis factor-α,TNF-α)和白细胞介素1β(Interleukin-1β,IL-1β)、心肌酶谱磷酸肌酸激酶(Creative kinase,CK)和乳酸脱氢酶(Lactic dehydrogenase,LDH)、心肌损伤标志物心肌肌钙蛋白T(Cardiac troponin T,cTnT)和B型尿钠肽(Brain natriuretic peptide,BNP)的水平;双荧光素酶报告基因检验miR-223-3p和FOXO1之间的靶向关系.实验结果显示,三七总黄酮能够缓解病毒性心肌炎模型细胞的炎症反应及细胞损伤,并显著上调模型细胞中miR-223-3p的水平.敲除模型细胞中的miR-223-3p能够逆转三七总黄酮对病毒性心肌炎的治疗作用.通过双荧光素酶报告基因实验验证miR-223-3p靶向负调控FOXO1蛋白的表达.进一步研究发现,过表达FOXO1可抑制三七总黄酮对病毒性心肌炎的治疗作用;但同时过表达miR-223-3p后,过表达FOXO1对三七总黄酮疗效的抑制作用被逆转.由此得出结论,三七总黄酮可缓解病毒性心肌炎模型细胞的炎症反应及细胞损伤,其作用机制是通过调控miR-223-3p/FOXO1分子轴实现的.     

病毒性心肌炎和扩张性心肌病的研究进展

病毒性心肌炎是一种常见的疾病,一般不引起严重后果。然而在有些病例中可以引起严重的心肌损伤和急性心力衰竭。它有时也可以演变成进行性的慢性心力衰竭。近年的研究致力于阐明病毒感染后心肌务的复杂机制,这些研究证明心肌损伤是由免疫和病毒双重机制所介导的。急性心肌炎可以有不同的临床表现,它也可以是健康青年人的猝死原因。临床和实验研究表明α1－受体阻滞剂、卡替洛尔、维拉帕米、血管紧张素转换酶抑制剂治疗有效。抗病毒药物的应用应受到重视。临床上免疫抑制剂治疗病毒性心肌炎效果不明显,而免疫调节治疗有望成为有意义的治疗方法。     

武汉地区小儿心肌炎病毒病因初探

本文介绍武汉地区小儿病毒性心肌炎病原调查结果。33例小儿急性心肌炎患者,取其粪便、咽拭子或心肌组织进行病毒分离,并采集患者急性与恢复期血清,用微量中和试验检测对Coxsackie B组6个型病毒的抗体增长情况。结果从26例分离出7株病毒,同时伴有对同型毒株双份抗体四倍或四倍以上增长者4例。1例为CoxsackieB_3,3例为腺病毒。对22例双份血清抗体检测结果:有13例分别对Coxsackie B组2、4、3型抗体有4倍以上增长,阳性率为59％。表明CoxsackieB组病毒为武汉地区小儿病毒性心肌炎重要病因。但腺病毒在病毒性心肌炎中的病原作用亦不容忽视。     

柯萨奇B3病毒性心肌炎的免疫抗炎症研究

病毒性心肌炎(viral myocarditis,VMC)属感染性心肌疾病,可由多种病毒诱导,其中以柯萨奇B组3型病毒(Coxsackie virus B3,CVB3)最为常见。由CVB3引起的VMC典型表现为心肌细胞炎症反应所导致的心肌损伤和坏死,并最终发展为慢性炎症或扩张性心肌病,在人类有很高的发病率和致死率。目前,柯萨奇B3病毒性心肌炎抗炎症治疗措施仍不完善,且相关免疫抗炎症治疗机理未完全阐明,因此探索其免疫抗炎症治疗机理和作用可能成为治疗柯萨奇B3病毒性心肌炎的重要靶点。现主要从Wnt11基因、巨噬细胞、半乳糖凝集素3、锌指抗病毒蛋白、蜂毒素和丙戊酸6个免疫抗炎症相关方面,对柯萨奇B3病毒性心肌炎的最新免疫抗炎症研究予以综述。     

C-myc蛋白的表达与小鼠病毒性心肌炎心肌细胞凋亡的关系

细胞凋亡（apoPthei一是指在活组织中,单个细胞受其内在基因的编程调控,通过节动的生化过程而‘咱杀”死亡的现象,是机体正常生理过程。近年来研究发现,细胞凋C参与多种疾病的发生与发展。实验通过对病毒性心肌炎（VMC）小鼠心肌细胞调C及凋亡相关基因C－myC蛋白进行检测,旨在探讨VMC、细胞凋亡和C一mp蛋白三者Z间关系。给出几出C／J‘鼠腹腔接种啥鼠心肌100TCIqo柯萨奇B3病毒（CWhm）0．Ind诱发急性病毒性心肌炎,感染病毒gd后,断脊处死小鼠,取心肌组织分别进行石蜡包理及相关检查。光学显微镜检查,发现小鼠心肌组织有广…     

急性重症病毒性心肌炎的临床特征分析

目的:探讨急性重症病毒性心肌炎的临床特征及心脏彩超和血清心肌损伤标志物对重症病毒性心肌炎的早期临床诊断价值。方法:回顾性分析2013年6月至2015年8月入住我院心脏科的临床诊断为急性心肌炎的患者27例,其中符合急性重症心肌炎诊断标准的患者10例,其余17例为非重症心肌炎,另选取10例入院检查后排除心血管疾病的患者为健康对照组。对三组患者的一般临床资料、心脏彩超结果及心肌损伤标志物结果进行分析,选取有统计学差异的指标行ROC曲线分析得出预测重症心肌炎的效能。结果:重症心肌炎组左室室间隔厚度、左室后壁厚度、左房内径、血浆B型尿钠肽较其余两组显著增高,进一步行ROC曲线分析提示左室室间隔厚度、左室后壁厚度预测重症心肌炎的敏感性分别为80%、70%,特异性均为94%,临界值分别为0.855 cm、0.875 cm。结论:急性心肌炎患者室壁厚度增加,当左室室间隔厚度0.855 cm或左室后壁厚度0.875 cm时需引起重视,警惕患者可能进展至重症病毒性心肌炎。     

小鼠外周血心肌特异性microRNAs 的变化与病毒性心肌炎 相关关系初探

目的:通过识别病毒性心肌炎小鼠和正常小鼠血浆中miR-1,miR-133,miR-206表达量的差异,分析外周血中心肌特异性microRNAs的变化与病毒性心肌炎相关关系,为探索miRNAs作为病毒性心肌炎诊断的生物标志物提供可行性的研究资料。方法:在小鼠病毒性心肌炎模型的基础上,采用荧光定量PCR方法,检测病毒性心肌炎急性期小鼠组和正常小鼠组血浆中相关miRNAs含量,并进行统计学分析。再于病毒注射后1d,3d,5d,7d,9d,11d,分别处死病毒小鼠,观察血浆miRNAs的动态变化规律。同时用Elisa检测心肌肌钙蛋白的变化,对目的 miRNAs与心肌肌钙蛋白进行相关性分析。结果:急性期时三种miRNAs血浆含量显著上调。病毒注射后3d开始上升明显,并持续保持在较高水平到7d,于9d时开始下降。发病期间,血浆miRNAs含量与心肌肌钙蛋白呈现良好的正相关性。结论:小鼠外周血中心肌特异性microRNAs在病毒性心肌炎发病过程中的呈现明显上调并与病程和相应指标存在相关关系,为miRNAs作为病毒性心肌炎诊断的生物标志物提供了重要线索。     

30例病毒性心肌炎法医病理学分析

目的:回顾性分析30例病毒性心肌炎的法医病理学特点,为病毒性心肌炎的法医学鉴定提供依据。方法:采用昆明医科大学司法鉴定中心2003年至2014年的30例病毒性心肌炎法医病理鉴定案例进行回顾性分析。结果:30例死亡原因均为病毒性心肌炎致急性心功能障碍死亡,大多为重型病毒性心肌炎,均累及心肌损害,心肌细胞水肿,基质溶解坏死;心肌肌间多量淋巴细胞浸润;局部心肌束排列紊乱,间质纤维组织增生,同时不同程度伴有肺、脑、扁桃体等器官组织的损害。结论:重型病毒性心肌炎起病急,临床症状不典型,进程快,易造成误诊误治,死亡率高,产生医疗纠纷,需要法医学鉴定。病毒性心肌炎法医学鉴定时,以心脏大体所见和组织学观察为主要依据,同时还要特别注意其他机械性损伤,辨别每个死亡原因之间的关系,必要时结合特殊检查,例如对趋化因子MCP-1的检测。     

CVB3诱导的急性心肌炎C57BL/6小鼠模型转录组分析

研究柯萨奇病毒B3(CVB3)感染小鼠所引起的心肌组织转录组变化规律.C57BL/6小鼠腹腔接种浓度为104TCID50的CVB3,建立C57BL/6急性病毒性心肌炎小鼠模型,逐日测量休重.接种第3、6、9、11和14d分别取心脏,计算心脏指数,并取部分心肌组织进行HE染色分析病理学改变;病毒接种后的第3、第6和第9d,取部分组织匀浆进行转录组测序,分析三个时间点的共同差异表达基因,对其进行GO和KEGG信号通路的富集,并对其中12个基因进行了 qRT-PCR的验证.在CVB3感染后,小鼠体重下降至对照组的80％,心脏指数在第3d明显升高,随后逐渐下降.通过转录组分析找到100个共同差异基因,从中选出的12个基因,经qRT-PCR验证与转录组表达趋势一致.GO和KEGG信号通路富集发现,CVB3感染后,小鼠心肌组织出现病毒性心肌炎、NK细胞通路,T、B细胞激活及先天性免疫反应通路的改变.差异基因的蛋白与蛋白互作网络分析显示,先天性免疫中MHC-Ⅰ型分子蛋白基因H2-Q7、H2-Kl、H2-D1等,NK细胞毒作用通路中的Gzmb、Gzma,以及蛋白酶体信号通路基因Psmb8、 Psmb9﹑Psmb10和lfit3位于相互作用中心.CVB3感染C57BL/6小鼠心肌组织的转录组变化涉及病毒性心肌炎、NK细胞和T、B细胞激活及先天性免疫反应等通路.CVB3感染引起的急性病毒性心肌炎是多通路和多基因综合作用的结果.     

Cardioprotective effects of carvedilol on acute autoimmune myocarditis: anti-inflammatory effects associated with antioxidant property

Carvedilol, a new beta-blocker with antioxidant properties, has been shown to be cardioprotective in experimental models of myocardial damage. We investigated whether carvedilol protects against experimental autoimmune myocarditis (EAM) because of its suppression of inflammatory cytokines and its antioxidant properties. We orally administered a vehicle, various doses of carvedilol, racemic carvedilol [R(+)-carvedilol, an enantiomer of carvedilol without beta-blocking activity], metoprolol, or propranolol to rats with EAM induced by porcine myosin for 3 wk. Echocardiographic study showed that the three beta-blockers, except R(+)-carvedilol, suppressed left ventricular fractional shortening and decreased heart rates to the same extent. Carvedilol and R(+)-carvedilol, but not metoprolol or propranolol, markedly reduced the severity of myocarditis at the two different doses and suppressed thickening of the left ventricular posterior wall in rats with EAM. Only carvedilol suppressed myocardial mRNA expression of inflammatory cytokines and IL-1beta protein expression in myocarditis. In addition, carvedilol and R(+)-carvedilol decreased myocardial protein carbonyl contents and myocardial thiobarbituric acid-reactive substance products in rats with EAM. The in vitro study showed that carvedilol and R(+)-carvedilol suppressed IL-1beta production in LPS-stimulated U937 cells and that carvedilol and R(+)-carvedilol, but not metoprolol or propranolol, suppressed thiobarbituric acid-reactive substance products in myocardial membrane challenged by oxidative stress. It was also confirmed that probucol, an antioxidant, ameliorated EAM in vivo. Carvedilol protects against acute EAM in rats, and the superior cardioprotective effect of carvedilol compared with metoprolol and propranolol may be due to suppression of inflammatory cytokines associated with the antioxidant properties in addition to the hemodynamic modifications.     

病毒性心肌炎所致小鼠心力衰竭心肌组织内质网应激相关的凋亡关系的研究

目的：探讨病毒性心肌炎心力衰竭小鼠心肌组织内质网应激介导的凋亡途径。方法：40只雄性Balb／c小鼠分为病毒性心肌炎组和正常对照组（n=20）,病毒性心肌炎组应用柯萨奇B3病毒制作BALB／c小鼠病毒性心肌炎模型,观察小鼠的一般情况,7d行血流动力学检查后处死取心脏标本,用TUNEL法检测心肌细胞凋亡,RT-PCR检测心肌细胞内质网伴侣蛋白葡萄糖调节蛋白（GAP）78和GRP04的mRNA表达水平。结果：①与正常对照组相比,病毒性心肌炎组小鼠血流动力学指标明显降低（P〈0．01）;②TUNEL染色显示病毒性心肌炎心力衰竭小鼠心肌组织凋亡明显增多（P〈0．01）;③病毒性心肌炎组小鼠内质网伴侣蛋白GRP78和GRP94的mRNA表达水平均明显高于对照组（P〈0．01）。结论：病毒性心肌炎心力衰竭小鼠内质网应激可能介导了心肌细胞凋亡。     

Impairment of immunoproteasome function by β5i/LMP7 subunit deficiency results in severe enterovirus myocarditis

Proteasomes recognize and degrade poly-ubiquitinylated proteins. In infectious disease, cells activated by interferons (IFNs) express three unique catalytic subunits β1i/LMP2, β2i/MECL-1 and β5i/LMP7 forming an alternative proteasome isoform, the immunoproteasome (IP). The in vivo function of IPs in pathogen-induced inflammation is still a matter of controversy. IPs were mainly associated with MHC class I antigen processing. However, recent findings pointed to a more general function of IPs in response to cytokine stress. Here, we report on the role of IPs in acute coxsackievirus B3 (CVB3) myocarditis reflecting one of the most common viral disease entities among young people. Despite identical viral load in both control and IP-deficient mice, IP-deficiency was associated with severe acute heart muscle injury reflected by large foci of inflammatory lesions and severe myocardial tissue damage. Exacerbation of acute heart muscle injury in this host was ascribed to disequilibrium in protein homeostasis in viral heart disease as indicated by the detection of increased proteotoxic stress in cytokine-challenged cardiomyocytes and inflammatory cells from IP-deficient mice. In fact, due to IP-dependent removal of poly-ubiquitinylated protein aggregates in the injured myocardium IPs protected CVB3-challenged mice from oxidant-protein damage. Impaired NFκB activation in IP-deficient cardiomyocytes and inflammatory cells and proteotoxic stress in combination with severe inflammation in CVB3-challenged hearts from IP-deficient mice potentiated apoptotic cell death in this host, thus exacerbating acute tissue damage. Adoptive T cell transfer studies in IP-deficient mice are in agreement with data pointing towards an effective CD8 T cell immune. This study therefore demonstrates that IP formation primarily protects the target organ of CVB3 infection from excessive inflammatory tissue damage in a virus-induced proinflammatory cytokine milieu.     

The importance of cardiac MRI as a diagnostic tool in viral myocarditis-induced cardiomyopathy

Myocarditis is an acute or chronic inflammatory disease of the myocardium which can be viral, postinfectious immune or primarily organ-specific autoimmune. Clinical manifestations of acute and chronic myocarditis are extremely varied, ranging from mild to severe. Affected patients may recover or develop (dilated) cardiomyopathy (DCM) with life-threatening symptoms including heart failure, conduction disturbances, arrhythmias, cardiogenic shock or sudden cardiac death. The diagnosis of myocarditis is a challenging process and not only because of a diverse presentation; other problems are limited sensitivity of endomyocardial biopsies (EMB) and overlapping symptoms. Furthermore, the diagnosis is not well defined. However, early diagnosis is mandatory to address specific aetiology-directed therapeutic management in myocarditis that influences patient morbidity and mortality. Currently, EMB remains the only way to confirm the presence of a viral genome and other histopathological findings allowing proper treatment to be implemented in cases of myocarditis. Increased recognition of the role of myocardial inflammatory changes has given rise to interest in noninvasive imaging as a diagnostic tool, especially cardiovascular magnetic resonance imaging (CMR). In this review we discuss the current role of CMR in the evaluation of myocarditis-induced inflammatory cardiomyopathies. (Neth Heart J 2009;17:481–6.)     

Caspase inhibition protects against reovirus-induced myocardial injury in vitro and in vivo

Viral myocarditis is a disease with a high morbidity and mortality. The pathogenesis of this disease remains poorly characterized, with components of both direct virus-mediated and secondary inflammatory and immune responses contributing to disease. Apoptosis has increasingly been viewed as an important mechanism of myocardial injury in noninfectious models of cardiac disease, including ischemia and failure. Using a reovirus murine model of viral myocarditis, we characterized and targeted apoptosis as a key mechanism of virus-associated myocardial injury in vitro and in vivo. We demonstrated caspase-3 activation, in conjunction with terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling and annexin binding, in cardiac myocytes after myocarditic viral infection in vitro. We also demonstrated a tight temporal and geographical correlation between caspase-3 activation, histologic injury, and viral load in cardiac tissue after myocarditic viral infection in vivo. Two pharmacologic agents that broadly inhibit caspase activity, Q-VD-OPH and Z-VAD(OMe)-FMK, effectively inhibited virus-induced cellular death in vitro. The inhibition of caspase activity in vivo by the use of pharmacologic agents as well as genetic manipulation reduced virus-induced myocardial injury by 40 to 60% and dramatically improved survival in infected caspase-3-deficient animals. This study indicates that apoptosis plays a critical role in mediating cardiac injury in the setting of viral myocarditis and is the first demonstration that caspase inhibition may serve as a novel therapeutic strategy for this devastating disease.     

Propranolol ameliorates and epinephrine exacerbates progression of acute and chronic viral myocarditis

Recent studies point to important interactions between proinflammatory cytokines and neurohumoral mediators in heart failure. Here we investigate the influence of the beta-adrenergic system on cytokines and neurohumoral factors and the sequelae of viral myocarditis. In an experimental model with virus-infected BALB/c mice, we studied the acute and chronic effects of epinephrine and propranolol on myocardial morphology, cytokine gene expression, and survival. BALB/c mice were inoculated with the encephalomyocarditis virus (EMCV) or sham inoculated with saline and followed for 30 days. Epinephrine increased the severity of inflammatory cell infiltration and myocardial necrosis induced by EMCV. Gene expression of TNF-alpha, IL-6, and IL-10 was markedly enhanced by epinephrine in EMCV-inoculated mice. Survival rate after 30 days was reduced to 40% in epinephrine-treated EMCV-inoculated mice compared with 70% in untreated EMCV-inoculated mice (P < 0.05). Treatment with the beta-blocker propranolol significantly decreased mortality, myocardial necrosis, and infiltration of inflammatory cells in EMCV-inoculated mice. Propranolol also suppressed gene expression of TNF-alpha, IL-6, and IL-10. A single dose of epinephrine 120 days after EMCV inoculation caused sudden death in 70% of infected mice; propranolol significantly reduced incidence of death to 33%. These results indicate that acute and chronic stages of viral myocarditis are modulated by the beta-adrenergic system and its interactions with proinflammatory cytokines.     

Experimental Myocarditis Induced in Mice by Infection with Influenza A2 Virus

A mouse model was established for the study of acute myocarditis that occurs during influenza infection. Challenge with more than 10 LD₅₀ of mouse-adapted influenza A₂ virus (H₂N₂) induced myocarditis macroscopically discernible as white, irregularly shaped lesions which were shown by histological examination to consist of necrotic myofibers surrounded by infiltrating mononuclear inflammatory cells. After challenge with 10 LD₅₀ of the virus, macroscopic myocarditis was found to advance in a progressive manner up to the 7th day, while the virus titer in the heart reached its peak on the 2nd day and began to decrease on the 5th day of infection. However, development of myocarditis was significantly suppressed in mice which were irradiated with 400 R of X-rays before infection. In addition, myocarditis did not develop in congenitally athymic nude mice. These data indicate that myocarditis was not brought about by viral action directly, but that it was mediated by some function of the host against viral in-vasion, which was abolished by X-irradiation. The data also suggest that T cells played a key role in the development of myocarditis.     

The role of CD8+ T lymphocytes in coxsackievirus B3-induced myocarditis.

Coxsackievirus infections have previously been shown to cause acute or chronic myocarditis in humans, and several mouse models have been established to study the pathology of this disease. Myocardial injury may result from direct viral effects and/or may be immune mediated. To determine the relative roles of these processes in pathogenesis, we have compared coxsackievirus B3 (CVB3) infections of normal and immuno-compromised transgenic knockout (ko) mice. CVB3 was able to infect all strains used (C57BL/6, CD4ko, and beta-microglobulin ko [beta 2Mko]), and following intraperitoneal injection, two disease processes could be distinguished. First, the virus caused early (3 to 7 days postinfection) death in a viral dose-dependent manner. Immunocompetent C57BL/6 mice were highly susceptible (50% lethal dose = 70 PFU), while immunodeficient transgenic ko mice were less susceptible, showing 10- and 180-fold increases in the 50% lethal dose (for CD4ko and beta 2Mko mice, respectively). Second, a histologic examination of surviving CD4ko mice at 7 days postinfection revealed severe myocarditis; the inflammatory infiltrate comprised 40 to 50% macrophages, 30 to 40% NK cells, and 10 to 20% CD8+ T lymphocytes. The infiltration resolved over the following 2 to 3 weeks, with resultant myocardial fibrosis. In vivo depletion of CD8+ T lymphocytes from these CD4ko mice led to a marked reduction in myocarditis and an increase in myocardial virus titers. beta 2Mko mice, which lack antiviral CD8+ T cells, are much less susceptible to early death and to the development of myocarditis. We conclude that our data support a strong immunopathologic component in CVB3-induced disease and implicate both CD4+ and CD8+ T cells. Compared with immunocompetent animals, (i) mice lacking CD4+ T cells (CD4ko) were more resistant to virus challenge, and (ii) mice lacking CD8+ T cells (beta 2Mko and in vivo-depleted CD4ko) showed enhanced survival and a reduced incidence of the later myocarditis. Nevertheless, the picture is complex, since (iii) removal of the CD4+ component, while protecting against early death, greatly magnified the severity of myocarditis, and (iv) removal of the CD8+ cells from CD4ko mice, although protecting against early death and later myocarditis, led to markedly increased virus titers in the heart. These data underscore the complex balance between the costs and benefits of effective antiviral immune responses.     

Reovirus-induced acute myocarditis in mice correlates with viral RNA synthesis rather than generation of infectious virus in cardiac myocytes.

The capacity for different reovirus reassortant viruses to induce acute myocarditis in mice correlates with cytopathogenic effect in primary cultures of murine cardiac myocytes. Multiple viral genes encoding proteins involved in viral RNA synthesis are determinants of this disease. We therefore evaluated the role of viral RNA synthesis in induction of acute myocarditis by infecting primary cultures of cardiac myocytes with a panel of myocarditic and nonmyocarditic viruses and quantitating RNA synthesis. RNA synthesis correlated with induction of myocarditis and with the S1 and M1 reovirus genes. Since one consequence of viral RNA synthesis is generation of infectious virus, we looked next at viral yield from cardiac myocyte cultures. Yield of infectious virus at an early time postinfection or as a final yield from primary infections did not correlate with myocarditis, but instead both correlated with the S1 gene. The S1 gene also determined the fraction of cells infected during primary infections in the culture, which varied dramatically between viruses. Viral yields per infected cell were similar for most myocarditic and nonmyocarditic reoviruses and did not correlate with induction of myocarditis or any reovirus gene. Together, the data provide two insights into reovirus-induced acute myocarditis in mice. First, while the S1 gene. which encodes the viral attachment protein sigma1 (as well as a nonstructural protein, sigma1s, of unknown function) does not determine the myocarditic potential of these viruses, it does determine the efficiency with which they infect cardiac myocytes. Second, while viral RNA synthesis is a determinant of acute myocarditis, this is not due to generation of infectious virus. This finding suggests that some other consequence of viral RNA synthesis, for example, induction of interferon, may determine reovirus-induced acute myocarditis.