To clarify immune-mediated mechanisms in rheumatic heart disease caused by group A streptococcal infection, valve tissues from rheumatic patients with valvular heart disease who required valve replacement were studied for reactivity with monoclonal anti-CD4 or anti-CD8 monoclonal antibodies or anti-vascular cell adhesion molecule-1 (VCAM-1). At the valve surface, CD4(+) and CD8(+) T lymphocytes were adherent to valve endothelium and penetrated through the subendothelial layer. T cell extravasation into the valve through the surface valvular endothelium appeared to be an important event in the development of rheumatic heart disease. VCAM-1 was expressed on the valvular endothelium in rheumatic valves. Evidence suggested that the pathogenesis of rheumatic heart disease involved the activation of surface valvular endothelium with the expression of VCAM-1 and the extravasation of CD4(+) and CD8(+) lymphocytes through the activated endothelium into the valve. Lymphocytic infiltration through the valve surface endothelium has not been appreciated as a potential initiating step in disease pathogenesis.

In human myocarditis and its sequela dilated cardiomyopathy (DCM), the mechanisms and immune phenotype governing disease and subsequent heart failure are not known. Here, we identified a Th17 cell immunophenotype of human myocarditis/DCM with elevated CD4+IL17+ T cells and Th17-promoting cytokines IL-6, TGF-β, and IL-23 as well as GM-CSF–secreting CD4+ T cells. The Th17 phenotype was linked with the effects of cardiac myosin on CD14+ monocytes, TLR2, and heart failure. Persistent heart failure was associated with high percentages of IL-17–producing T cells and IL-17–promoting cytokines, and the myocarditis/DCM phenotype included significantly low percentages of FOXP3+ Tregs, which may contribute to disease severity. We demonstrate a potentially novel mechanism in human myocarditis/DCM in which TLR2 peptide ligands from human cardiac myosin stimulated exaggerated Th17-related cytokines including TGF-β, IL-6, and IL-23 from myocarditic CD14+ monocytes in vitro, and an anti-TLR2 antibody abrogated the cytokine response. Our translational study explains how an immune phenotype may be initiated by cardiac myosin TLR ligand stimulation of monocytes to generate Th17-promoting cytokines and development of pathogenic Th17 cells in human myocarditis and heart failure, and provides a rationale for targeting IL-17A as a therapeutic option.

The mechanisms by which autoantibodies against cardiac myosin (CM) may lead to heart dysfunction is unknown. We show that autoantibodies to CM in anti-CM sera and mAbs derived from experimental autoimmune myocarditis targeted the heart cell surface and induced Ab-mediated cAMP-dependent protein kinase A activity. Ab-mediated cell signaling of protein kinase A was blocked by CM, anti-IgG, or by specific inhibitors of the β-adrenergic receptor (β-AR) pathway. mAbs confirmed mimicry between CM and the β-AR. Passive transfer of purified Ab (IgG) from CM-immunized rats resulted in IgG deposition and apoptosis in the heart, leading to a cardiomyopathic heart disease phenotype in recipients. Our novel findings link anti-CM Ab with the β-AR and subsequent Ab-mediated cell signaling in the heart.

Rheumatic heart disease is an autoimmune sequela of group A streptococcal infection. Previous studies have established that streptococcal M protein is structurally and immunologically similar to cardiac myosin, a well-known mediator of inflammatory heart disease. In this study, we investigated the hypothesis that streptococcal M protein could produce inflammatory valvular heart lesions similar to those seen in rheumatic fever (RF). Fifty percent (3 of 6) of Lewis rats immunized with recombinant type 6 streptococcal M protein (rM6) developed valvulitis as well as focal lesions of myocarditis. Valvular lesions initiated at the valve surface endothelium spread into the valve. Anitschkow cells and verruca-like lesions were present. T cells from rM6-immunized rats proliferated in the presence of purified cardiac myosin, but not skeletal myosin. A T-cell line produced from rM6-treated rats proliferated in the presence of cardiac myosin and rM6 protein. The study demonstrates that the Lewis rat is a model of valvular heart disease and that streptococcal M protein can induce an autoimmune cell-mediated immune attack on the heart valve in an animal model. The data support the hypothesis that a bacterial antigen can break immune tolerance in vivo, an important concept in autoimmunity.

The influence of the endothelial protein C receptor (EPCR) on the host response to Escherichia coli was studied. Animals were treated with 4 separate protocols for survival studies and analysis of physiologic and biochemical parameters: (1) monoclonal antibody (mAb) that blocks protein C/activated protein C binding to EPCR plus sublethal numbers of E coli (SLEC) (n = 4); (2) mAb to EPCR that does not block binding plus SLEC (n = 3); (3) SLEC alone (n = 4); and (4) blocking mAB alone (n = 1). Those animals receiving blocking mAb to EPCR plus sublethal E coli died 7 to 54 hours after challenge, whereas all animals treated with the other protocols were permanent survivors. Histopathologic studies of tissues from animals receiving blocking mAb plus SLEC removed at postmortem were compared with those animals receiving SLEC alone killed at T+24 hours. The animals receiving the blocking mAb exhibited consumption of fibrinogen, microvascular thrombosis with hemorrhage of both the adrenal and renal cortex, and an intense influx of neutrophils into the adrenal, renal, and hepatic microvasculature, whereas the tissues from animals receiving only sublethal E coli exhibited none of these abnormal histopathologic changes. Compared with the control animals, the animals receiving the blocking mAb exhibited significantly elevated serum glutamic pyruvic transaminase, anion gap, thrombin-antithrombin complex, IL-6, IL-8, and soluble thrombomodulin. The levels of circulating activated protein C varied too widely to allow a clear determination of whether the extent of protein C activation was altered in vivo by blocking protein C binding to EPCR. We conclude that protein C/activated protein C binding to EPCR contributes to the negative regulation of the coagulopathic and inflammatory response to E coli and that EPCR provides an additional critical step in the host defense against E coli.