Effect of valvular surgery on antibody to the group A streptococcal carbohydrate

The Role of Inflammation and Oxidative Stress in Rheumatic Heart Disease

Rheumatic heart disease (RHD), an acquired valvular disease, remains an important cause of morbidity and mortality in developing countries. This chronic illness starts from untreated streptococcal throat infection, resulting in acute rheumatic fever (ARF) in susceptible individuals. Repeated infections lead to a chronic phase characterized by the damage of heart valves. Inflammation has been found to play important role in the development of this disease. All the studies presented in this review clearly show the involvement of the inflammatory state in the progression of this disease. However, the exact role of cytokines in inflammation sites remains to be examined, since most studies have so far focused on peripheral blood. Such analysis would provide information on inflammatory mechanisms in situ.

Rheumatic Heart Valve Disease Pathophysiology and Underlying Mechanisms

Rheumatic heart valve disease (RHVD) is a post-infectious sequel of acute rheumatic fever resulting from an abnormal immune response to a streptococcal pharyngitis that triggers valvular damage. RHVD is the leading cause of cardiovascular death in children and young adults, mainly in women from low and middle-income countries. It is known that long-term inflammation and high degree of fibrosis leads to valve dysfunction due to anatomic disruption of the valve apparatus. However, since public and private investments in RHVD studies are practically inexistent the number of publications is scarce. This disease shows different natural history and clinical presentations as compared to other degenerative heart valve diseases. Although more than five decades passed after the pioneering studies on the pathogenesis of RHVD, it is still unclear how self-tolerance mechanisms fail in this disease, and how humoral and cellular inflammatory responses are interconnected. Despite that pathological mechanisms have been already proposed for RHVD, none of them are able to explain the preferential involvement of the mitral valve. This review focuses on pathophysiology and underlying mechanisms of RHVD.

Rheumatic Heart Disease in the Twenty-First Century

Rheumatic heart disease (RHD) is a chronic valvular disease resulting after severe or repetitive episodes of acute rheumatic fever (ARF), an autoimmune response to group A Streptococcus infection. RHD has been almost eliminated with improved social and health infrastructure in affluent countries while it remains a neglected disease with major cause of morbidity and mortality in many low- and middle-income countries, and resource-limited regions of high-income countries. Despite our evolving understanding of the pathogenesis of RHD, there have not been any significant advances to prevent or halt progression of disease in recent history. Long-term penicillin-based treatment and surgery remain the backbone of a RHD control program in the absence of an effective vaccine. The advent of echocardiographic screening algorithms has improved the accuracy of diagnosing RHD and has shed light on the enormous burden of disease. Encouragingly, this has led to a rekindled commitment from researchers in the most affected countries to advocate and take bold actions to end this disease of social inequality.

The association of plasma high-sensitivity C-reactive protein level with rheumatic heart disease: The possible role of inflammation

Background

Currently, it is not clear whether recurrent traumatic events lead to progression of rheumatic heart disease (RHD) after the incident of acute rheumatic fever or a persistent inflammatory state at the site of the valves. The aim of this study was to assess the possible association between plasma high sensitive C Reactive Protein (hs-CRP) level as an indicator of inflammation and RHD.

Materials & methods

Ninety patients with RHD and 90 healthy controls who had undergone complete echocardiographic examination were enrolled in this cross-sectional study. A score was given to each patient according to the severity of valvular involvement. Plasma hs-CRP level was checked for each patient by ELISA method twice with two-week interval, and the mean hs-CRP was calculated.

Results

The mean plasma hs-CRP level in the case group was significantly higher compared to its level in the control group (2.59 ± 4.82 and 0.55 ± 0.43 in the case and control groups respectively, p < 0.001). There was also a strong association between the level of plasma hs-CRP and the severity of rheumatic valvular involvement (p < 0.001).

Conclusion

The mean plasma hs-CRP level seems to have a significant association with RHD and its severity. Further studies are needed to determine the cause and effect relationship.

Rheumatic Heart Disease: The Unfinished Global Agenda

Primarily affecting the young, rheumatic heart disease (RHD) is a neglected chronic disease commonly causing premature morbidity and mortality among the global poor. Standard clinical prevention and treatment is based on studies from the early antimicrobial era, as research investment halted soon after the virtual eradication of the disease from developed countries. The emergence of new global data on disease burden, new technologies, and a global health equity platform have revitalized interest and investment in RHD. This review surveys past and current evidence for standard RHD diagnosis and treatment, highlighting gaps in knowledge.

Update on rheumatic heart disease

PURPOSE OF REVIEW

The purpose is to provide a broad overview of the current state of knowledge of pathogenesis, diagnosis, and management of rheumatic heart disease (RHD).

RECENT FINDINGS

Studies on pathogenesis of RHD have focused on autoimmunity because of molecular mimicry between the streptococcal M antigen α-helical coiled-coil structure and sarcomeric proteins such as myosin and tropomyosin. More recently, nonsarcomeric autoantigens, endothelial injury and the innate immune system have been proposed to play key roles in the pathogenesis of RHD. In the 2015 revised Jones Criteria, the importance of echocardiography and subclinical carditis in the diagnosis of acute rheumatic fever is highlighted. Experimental studies with targeted anti-inflammatory therapeutics have been largely unsuccessful and the only established treatment is still lifelong antibiotics. Efforts to improve patient selection and outcomes with percutaneous mitral balloon valvuloplasty are ongoing. With regard to surgical management, several groups have demonstrated excellent operative and midterm outcomes from valve repair as opposed to valve replacement.

SUMMARY

There are still many unanswered questions regarding RHD pathogenesis. The only accepted medical treatment is still long-term antibiotic therapy, whereas advances in mitral repair techniques have led to successful durable repairs being performed in high-volume, expert centers.

The classical lancefield antigen of group a Streptococcus is a virulence determinant with implications for vaccine design

Group A Streptococcus (GAS) is a leading cause of infection-related mortality in humans. All GAS serotypes express the Lancefield group A carbohydrate (GAC), comprising a polyrhamnose backbone with an immunodominant N-acetylglucosamine (GlcNAc) side chain, which is the basis of rapid diagnostic tests. No biological function has been attributed to this conserved antigen. Here we identify and characterize the GAC biosynthesis genes, gacA through gacL. An isogenic mutant of the glycosyltransferase gacI, which is defective for GlcNAc side-chain addition, is attenuated for virulence in two infection models, in association with increased sensitivity to neutrophil killing, platelet-derived antimicrobials in serum, and the cathelicidin antimicrobial peptide LL-37. Antibodies to GAC lacking the GlcNAc side chain and containing only polyrhamnose promoted opsonophagocytic killing of multiple GAS serotypes and protected against systemic GAS challenge after passive immunization. Thus, the Lancefield antigen plays a functional role in GAS pathogenesis, and a deeper understanding of this unique polysaccharide has implications for vaccine development.

Carotid intima media thickness and arterial stiffness in children with acute rheumatic fever

Acute rheumatic fever (ARF) and rheumatic heart disease (RHD) constitute important public health problems in developing countries. Inflammation is present both in the early and late stages of the diseases. Chronic inflammation is known to be associated with atherosclerosis. We hypothesize that subclinical atherosclerosis and arterial stiffness may increase due to the ongoing inflammation as well as the increased pulse pressure and left-ventricular systolic dysfunction in RHD. The purpose of the present study was to investigate carotid intima media thickness (CIMT) and carotid artery stiffness in patients with ARF. Forty patients in follow-up due to ARF in the age group of 7-16 years (disease duration 1-10 years) and 36 volunteered subjects with similar body mass index were included in the study. The subjects included in the present study were compared regarding M-mode echocardiographic parameters and CIMT as well as carotid arterial strain (CAS), carotid artery distensibility (CAD), beta stiffness index (βSI), and pressure-strain elasticity modulus (Ep) as carotid artery stiffness parameters. CIMT (0.52 ± 0.08 and 0.48 ± 0.07 mm, p = 0.01), βSI (5.29 ± 2.98 and 3.02 ± 1.30, p < 0.001), and Ep (426.53 ± 210.50 and 254.44 ± 104.69 p < 0.001) were increased, whereas CAS (0.11 ± 0.01 and 0.19 ± 0.09, p < 0.001) and CAD (10.27 ± 4.69 and 17.76 ± 14.41, p < 0.001) were decreased in patients with ARF compared with the control group. There was a positive correlation between pulse pressure and βSI (r = 0.25, p = 0.02) and Ep (r = 0.28, p = 0.01) in addition to a correlation between left atrial dilatation and CIMT (r = 0.55 p < 0.001) in patients with ARF. CIMT and carotid artery stiffness were increased in patients with ARF. Patients with ARF may have an increased risk of subclinical atherosclerosis and cardiovascular events.

Revisiting the pathogenesis of rheumatic fever and carditis

Rheumatic fever is one of the most-neglected ailments, and its pathogenesis remains poorly understood. The major thrust of research has been directed towards cross-reactivity between streptococcal M protein and myocardial α-helical coiled-coil proteins. M protein has also been the focus of vaccine development. The characteristic pathological findings suggest that the primary site of rheumatic-fever-related damage is subendothelial and perivascular connective tissue matrix and overlying endothelium. Over the past 5 years, a streptococcal M protein N-terminus domain has been shown to bind to the CB3 region in collagen type IV. This binding seems to initiate an antibody response to the collagen and result in ground substance inflammation. These antibodies do not cross-react with M proteins, and we believe that no failure of immune system and, possibly, no molecular mimicry occur in rheumatic fever. This alternative hypothesis shares similarity with collagen involvement in both Goodpasture syndrome and Alport syndrome.

Association of mannose-binding lectin gene polymorphism but not of mannose-binding serine protease 2 with chronic severe aortic regurgitation of rheumatic etiology

N-Acetylglucosamine (GlcNAc) is the major immunoepitope of group A streptococcal cell wall carbohydrates. Antistreptococcal antibodies cross-reactive with anti-GlcNAc and laminin are present in sera of patients with rheumatic fever. The cross-reactivity of these antibodies with human heart valvular endothelium and the underlying basement membrane has been suggested to be a possible cause of immune-mediated valve lesion. Mannose-binding lectin (MBL) encoded by the MBL2 gene, a soluble pathogen recognition receptor, has high affinity for GlcNAc. We postulated that mutations in exon 1 of the MBL2 gene associated with a deficient serum level of MBL may contribute to chronic severe aortic regurgitation (AR) of rheumatic etiology. We studied 90 patients with severe chronic AR of rheumatic etiology and 281 healthy controls (HC) for the variants of the MBL2 gene at codons 52, 54, and 57 by using a PCR-restriction fragment length polymorphism-based method. We observed a significant difference in the prevalence of defective MBL2 alleles between patients with chronic severe AR and HC. Sixteen percent of patients with chronic severe AR were homozygotes or compound heterozygotes for defective MBL alleles in contrast to 5% for HC (P = 0.0022; odds ratio, 3.5 [95% confidence interval, 1.6 to 7.7]). No association was detected with the variant of the MASP2 gene. Our study suggests that MBL deficiency may contribute to the development of chronic severe AR of rheumatic etiology.

Overexpression of transforming growth factor-beta 1 in the valvular fibrosis of chronic rheumatic heart disease

For the purpose of determining the pathogenic role of transforming growth factor-beta1 (TGF-beta 1) in the mechanism of chronic rheumatic heart disease, we evaluated the expression of TGF-beta 1, proliferation of myofibroblasts, and changes in extracellular matrix components including collagen and proteoglycan in 30 rheumatic mitral valves and in 15 control valves. High TGF-beta 1 expression was identified in 21 cases (70%) of rheumatic mitral valves, whereas only 3 cases (20%) of the control group showed high TGF-beta 1 expression (p<0.001). Additionally, increased proliferation of myofibroblasts was observed in the rheumatic valves. High TGF-beta1 expression positively correlated with the proliferation of myofibroblasts (p=0.004), valvular fibrosis (p<0.001), inflammatory cell infiltration (p=0.004), neovascularization (p=0.007), and calcification (p<0.001) in the valvular leaflets. The ratio of proteoglycan to collagen deposition inversely correlated with TGF-beta 1 expression in mitral valves (p=0.040). In conclusion, an ongoing inflammatory process, the expression of TGF-beta 1, and proliferation of myofibroblasts within the valves have a potential role in the valvular fibrosis, calcification, and changes in the extracellular matrix that lead to the scarring sequelae of rheumatic heart disease.

Increased levels of high sensitive C-reactive protein in patients with chronic rheumatic valve disease: evidence of ongoing inflammation

The precise pathogenetic mechanism(s) of rheumatic fever and rheumatic heart disease have never been defined. C-reactive protein (CRP) is increased in patients with acute rheumatic fever, but it is not known whether plasma levels increase in patients with chronic rheumatic valve disease. The aim of this study was to determine the role of inflammation detected by high sensitivity CRP (hs-CRP) levels in the progression of chronic rheumatic valve disease. A total of 113 patients with chronic rheumatic valve disease (81 women, 32 men; mean age 40+/-14 years, range 13-70), 51 patients with prosthetic valve(s) (31 women, 20 men; mean age 48+/-13 years, range 21-71) and 102 healthy subjects (68 women, 34 men, mean age 41+/-12 years, range 25-73), as a control group, were assessed. Patients with acute rheumatic fever, acute infection, inflammatory disease, malignancy, acute myocardial infarction and trauma were excluded. hs-CRP was determined using latex-enhanced immunonephelometric assays on a BN II analyzer (Behring). Transthoracic echocardiography was performed in all patients in order to evaluate valvular disease. Levels of hs-CRP were significantly higher in patients with chronic rheumatic heart disease than in patients with prosthetic valve(s) and healthy subjects (0.62+/-0.64 vs. 0.35+/-0.41 vs. 0.24+/-0.18 mg/l, P<0.01 and P<0.001 respectively). No correlation was observed between CRP and age, sex or functional capacity. We found that hs-CRP is increased in chronic rheumatic heart disease; this may indicate that inflammatory response still persists in the chronic phase.

Cytotoxic mAb from rheumatic carditis recognizes heart valves and laminin

Anti-streptococcal antibodies cross-reactive with N-acetyl-betaD-glucosamine (GlcNAc) and myosin are present in the sera of patients with rheumatic fever (RF). However, their role in tissue injury is not clear. In this study, we show that anti-GlcNAc/anti-myosin mAb 3.B6 from a rheumatic carditis patient was cytotoxic for human endothelial cell lines and reacted with human valvular endothelium and underlying basement membrane. Reactivity of mAb 3.B6 with the valve was inhibited by human cardiac myosin > laminin > GlcNAc. The mAb 3.B6 epitopes were localized in fragments of human cardiac myosin, including heavy meromyosin (HMM), the S1 subfragment, and two light meromyosin (LMM) peptides containing amino acid sequences KEALISSLTRGKLTYTQQ (LMM 1) and SERVQLLHSQNTSLINQK (LMM 33). A novel feature of mAb 3.B6 was its reactivity with the extracellular matrix protein laminin, which may explain its reactivity with the valve surface. A laminin A-chain peptide (HTQNT) that includes homology to LMM33 inhibited the reactivity of mAb 3.B6 with human valve. These data support the hypothesis that cross-reactive antibodies in rheumatic carditis cause injury at the endothelium and underlying matrix of the valve.

Echocardiographic appearance of flail aortic valve in a dog with infective endocarditis

A 4-year-old female Boxer was suffering from aortic valve endocarditis with perforation of the right coronary cusp resulting in a flail aortic cusp and subsequent acute aortic insufficiency. This flail aortic cusp was observed on M mode and two-dimensional endocardiograms as a free linear echostructure in the left ventricular outflow tract. Although rarely observed, a free linear echostructure seems more specific of a flail aortic valve than a shaggy echostructure, which can represent a free moving vegetation and thus be confusing. Severe acute aortic insufficiency resulted in an uncommon abnormal mitral valve motion in the absence of early mitral diastolic opening. The absence of early mitral valve opening was thought to be a consequence of coupled aortic regurgitation, reduced left ventricular compliance, and presumably delayed mitral valve opening secondary to coronary artery occlusion. An exaggerated septal diastolic dip accounted for the decreased transmitral inflow. All the usual contractility parameters were within normal range; subsequently, mitral valve motion alterations seem to be more reliable indicators of left ventricular dysfunction during acute aortic insufficiency.

The group specific polysaccharide antibody in children with non-suppurative sequelae of group A streptococcal infection

The kinetics of the group A specific polysaccharide antibody were studied in children with acute rheumatic fever who had no carditis, children with acute rheumatic fever who had carditis and developed rheumatic heard disease and in children with acute poststreptococcal glomerulonephritis. The children with rheumatic fever who had carditis and those who did not, were kept on continuous antistreptococcal prophylaxis. In the group of children who developed rheumatic heart disease the titer of the antibody at onset was significantly higher than those who had rheumatic fever but no carditis (P = 0.01). After a mean follow-up period of three years, a high titer was maintained in children who developed rheumatic heart disease only and was significantly higher than that found in children with rheumatic fever who had no carditis (P = 0.001) and in children with poststerptococcal nephritis (P = 0.001).

Rheumatogenic streptococci and autoimmunity

The uniqueness of the group A streptococcus in initiating a cardiodestructive disease in a limited segment of the human species, regardless of race or ethnic group, makes the quest for a unique host response to a specific streptococcal antigen an intriguing and persisting challenge for clinical investigators, particularly for those investigators interested in autoimmunity. New methodology is making possible more incisive research approaches. The defined streptococcal antigens that turn out to be epitopes identical with host tissues, such as the M protein/cardiac myosin model or the hyaluronate in the capsule of mucoid rheumatogenic strains, offer the opportunity for more incisive clinical investigations. The isolation and cultivation of cardiotoxic T cell clones directed against such epitopes shared by host and parasite may eventually be possible. We may then learn more about whether autoimmunity is indeed a factor in the pathogenesis of rheumatic heart disease.