Rheumatic fever, autoimmunity, and molecular mimicry: the streptococcal connection

Hello from the Other Side: How Autoantibodies Circumvent the Blood-Brain Barrier in Autoimmune Encephalitis

Antibodies against neuronal receptors and synaptic proteins are associated with autoimmune encephalitides (AE) that produce movement and psychiatric disorders. In order to exert their pathological effects on neural circuits, autoantibodies against central nervous system (CNS) targets must gain access to the brain and spinal cord by crossing the blood–brain barrier (BBB), a tightly regulated gateway formed by endothelial cells lining CNS blood vessels. To date, the pathogenic mechanisms that underlie autoantibody-triggered encephalitic syndromes are poorly understood, and how autoantibodies breach the barrier remains obscure for almost all AE syndromes. The relative importance of cellular versus humoral immune mechanisms for disease pathogenesis also remains largely unexplored. Here, we review the proposed triggers for various autoimmune encephalopathies and their animal models, as well as basic structural features of the BBB and how they differ among various CNS regions, a feature that likely underlies some regional aspects of autoimmune encephalitis pathogenesis. We then discuss the routes that antibodies and immune cells employ to enter the CNS and their implications for AE. Finally, we explore future therapeutic strategies that may either preserve or restore barrier function and thereby limit immune cell and autoantibody infiltration into the CNS. Recent mechanistic insights into CNS autoantibody entry indicate promising future directions for therapeutic intervention beyond current, short-lived therapies that eliminate circulating autoantibodies.

Regulatory gene mutation: a driving force behind group a Streptococcus strain- and serotype-specific variation

Data from multiple bacterial pathogens are consistent with regulator-encoding genes having higher mutation frequencies than the genome average. Such mutations drive both strain- and type- (e.g., serotype, haplotype) specific phenotypic heterogeneity, and may challenge public health due to the potential of variants to circumvent established treatment and/or preventative regimes. Here, using the human bacterial pathogen the group A Streptococcus (GAS; S. pyogenes) as a model organism, we review the types and regulatory-, phenotypic-, and disease-specific consequences of naturally occurring regulatory gene mutations. Strain-specific regulator mutations that will be discussed include examples that transform isolates into hyper-invasive forms by enhancing expression of immunomodulatory virulence factors, and examples that promote asymptomatic carriage of the organism. The discussion of serotype-specific regulator mutations focuses on serotype M3 GAS isolates, and how the identified rewiring of regulatory networks in this serotype may be contributing to a decades old epidemiological association of M3 isolates with particularly severe invasive infections. We conclude that mutation plays an outsized role in GAS pathogenesis and has clinical relevance. Given the phenotypic variability associated with regulatory gene mutations, the rapid examination of these genes in infecting isolates may inform with respect to potential patient complications and treatment options.

Predictors of recurrence in Sydenham's chorea: Clinical observation from a single center

OBJECTIVE

Sydenham's chorea is the most common cause of acquired chorea in children and is the major manifestation for acute rheumatic fever. Despite being known as a benign, self-limiting condition, recurrences and persistence of symptoms can be seen. In this study, we aimed to evaluate retrospectively the clinical and laboratory features of patients with Sydenham's chorea and the rate and the course of recurrences, and to assess the risk of recurrences.

METHODS

The study was a retrospective study conducted in a tertiary hospital. Patients with Sydenham's chorea who were admitted to our outpatient clinics between January 2013 and June 2015 were included. Both newly diagnosed and follow-up patients were enrolled during this period. We retrospectively reviewed the medical charts of the patients.

RESULTS

There were 90 patients with female predominance. The mean age of onset was 11±2.4years. Complete remission was maintained in 77 patients (85.6%) at 1-6months and 4 patients had symptoms at more than 12months. Patients were followed for 6months to 9years. The recurrence rate was 16%. When we compared recurrent patients with the non-recurrent group, complete remission in 6months, the presence of persistent chorea, and regular use of prophylaxis were significantly different between the 2 groups.

CONCLUSIONS

Sydenham's chorea is still an important health problem and has high morbidity in patients with recurrent and persistent chorea. The irregular usage of antibiotic prophylaxis, failure to achieve remission within 6months, and prolongation of symptoms for more than 1year are risk factors for recurrence of chorea.

Cardiac Myosin Epitopes Recognized by Autoantibody in Acute and Convalescent Rheumatic Fever

BACKGROUND

Acute rheumatic fever (ARF) is an autoimmune disorder associated with Streptococcus pyogenes infection. A prevailing hypothesis to account for this disease is that epitopes of self-antigens, such as cardiac myosin react to antibodies against S. pyogenes. The goal of our study was to confirm disease epitopes of cardiac myosin, identify immunodominant epitopes and to monitor the epitope response pattern in acute and convalescent rheumatic fever.

METHODS

Enzyme-linked immunosorbant assays were used to determine epitopes immunodominant in acute disease and to track the immune response longitudinally to document any changes in the epitope pattern in convalescent sera. Multiplex fluorescence immunoassay was used to correlate anti-streptolysin O (ASO) and anti-human cardiac myosin antibodies.

RESULTS

Disease-specific epitopes in rheumatic fever were identified as S2-1, 4 and 8. Epitopes S2-1, 4, 8 and 9 were found to be immunodominant in acute sera and S2-1, 8, 9, 29 and 30 in the convalescent sera. Frequency analysis showed that 50% of the ARF subjects responded to S2-8. S2-8 responders tended to maintain their epitope pattern throughout the convalescent period, whereas the S2-8 nonresponders tended to spread their responses to other epitopes later in the immune response. There was a significant correlation between anti-cardiac myosin and ASO titers. In addition, S2-8 responders showed elevated ASO titers compared with S2-8 non responders.

CONCLUSION

Our studies confirm the existence of S2-1, 4 and 8 as disease-specific epitopes. We provide evidence that cardiac myosin S2-8 responders remain epitope stable in convalescence, whereas S2-8 nonresponders shift to neoepitopes. Multiplex data indicated a correlation between elevated ASO and anti-human cardiac myosin antibody titers. Mapping of cardiac myosin epitopes recognized in rheumatic fever sera may identify immunophenotypes of rheumatic fever.

[Acute rheumatic fever and infectious-inflammatory diseases of the pharynx: the relationship, treatment, and prophylaxis]

The relationship between pharyngeal infections, such as tonsillitis and pharyngitis, caused by group A beta-hemolytic streptococci (BHSA) and acute rheumatic fever (ARF) is a well-established fact confirmed by numerous studies carried out along the following lines: epidemiological, immunological, therapeutic, and prophylactic. The currently available data provide an opportunity to discuss the existence of «rheumatogenic» BHSA strains exhibiting a number of characteristic clinical and morphological properties. According to the current recommendations penicillins remain the means of first-line therapy for the treatment of acute forms of BHSA-induced tonsillitis and pharyngitis, whereas the macrolides should be applied only as the alternative medications in the patients with intolerance to beta-lactam antibiotics. This article contains characteristics of BHSA-carrier state and the principal indications for the prescription of antibiotics to the patients with these conditions. The key principle of secondary medicamental prophylaxis of acute respiratory infections are expounded along with the main fines of future research on the problems associated with BHSA-induced pharyngeal infections.

CNS autoimmune disease after Streptococcus pyogenes infections: animal models, cellular mechanisms and genetic factors

Streptococcus pyogenes infections have been associated with two autoimmune diseases of the CNS: Sydenham's chorea (SC) and Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcus infections (PANDAS). Despite the high frequency of pharyngeal streptococcus infections among children, only a small fraction develops SC or PANDAS. This suggests that several factors in combination are necessary to trigger autoimmune complications: specific S. pyogenes strains that induce a strong immune response toward the host nervous system; genetic susceptibility that predispose children toward an autoimmune response involving movement or tic symptoms; and multiple infections of the throat or tonsils that lead to a robust T_h17 cellular and humoral immune response when untreated. In this review, we summarize the evidence for each factor and propose that all must be met for the requisite neurovascular pathology and behavioral deficits found in SC/PANDAS.

Acute rheumatic fever and rheumatic heart disease

Acute rheumatic fever (ARF) is the result of an autoimmune response to pharyngitis caused by infection with group A Streptococcus. The long-term damage to cardiac valves caused by ARF, which can result from a single severe episode or from multiple recurrent episodes of the illness, is known as rheumatic heart disease (RHD) and is a notable cause of morbidity and mortality in resource-poor settings around the world. Although our understanding of disease pathogenesis has advanced in recent years, this has not led to dramatic improvements in diagnostic approaches, which are still reliant on clinical features using the Jones Criteria, or treatment practices. Indeed, penicillin has been the mainstay of treatment for decades and there is no other treatment that has been proven to alter the likelihood or the severity of RHD after an episode of ARF. Recent advances - including the use of echocardiographic diagnosis in those with ARF and in screening for early detection of RHD, progress in developing group A streptococcal vaccines and an increased focus on the lived experience of those with RHD and the need to improve quality of life - give cause for optimism that progress will be made in coming years against this neglected disease that affects populations around the world, but is a particular issue for those living in poverty.

Xenobiotics and loss of tolerance in primary biliary cholangitis

Data from genome wide association studies and geoepidemiological studies established that a combination of genetic predisposition and environmental stimulation is required for the loss of tolerance in primary biliary cholangitis (PBC). The serologic hallmark of PBC are the presence of high titer anti-mitochondrial autoantibodies (AMA) that recognize the lipoyl domain of the mitochondrial pyruvate dehydrogenase E2 (PDC-E2) subunit. Extensive efforts have been directed to investigate the molecular basis of AMA. Recently, experimental data has pointed to the thesis that the breaking of tolerance to PDC-E2 is a pivotal event in the initial etiology of PBC, including environmental xenobiotics including those commonly found in cosmetics and food additives, suggesting that chemical modification of the PDC-E2 epitope may render its vulnerable to become a neo-antigen and trigger an immune response in genetically susceptible hosts. Here, we will discuss the natural history, genetics and immunobiology of PBC and structural constraints of PDC-E2 in AMA recognition which makes it vulnerable to chemical modification.

Autoimmunity against dopamine receptors in neuropsychiatric and movement disorders: a review of Sydenham chorea and beyond

Antineuronal autoantibodies are associated with the involuntary movement disorder Sydenham chorea (SC) and paediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) which are characterized by the acute onset of tics and/or obsessive compulsive disorder (OCD). In SC and PANDAS, autoantibodies signal human neuronal cells and activate calcium calmodulin-dependent protein kinase II (CaMKII). Animal models immunized with group A streptococcal antigens demonstrate autoantibodies against dopamine receptors and concomitantly altered behaviours. Human monoclonal antibodies (mAbs) derived from SC target and signal the dopamine D2L (long) receptor (D2R). Antibodies against D2R were elevated over normal levels in SC and acute-onset PANDAS with small choreiform movements, but were not elevated over normal levels in PANDAS-like chronic tics and OCD. The expression of human SC-derived anti-D2R autoantibody V gene in B cells and serum of transgenic mice demonstrated that the human autoantibody targets dopaminergic neurones in the basal ganglia and other types of neurones in the cortex. Here, we review current evidence supporting the hypothesis that antineuronal antibodies, specifically against dopamine receptors, follow streptococcal exposures and may target dopamine receptors and alter central dopamine pathways leading to movement and neuropsychiatric disorders.

IL10 Promoter Polymorphisms are Associated with Rheumatic Heart Disease in Saudi Arabian Patients

Rheumatic heart disease (RHD) is an inflammatory disease that develops following streptococcal infections. IL10 helps to balance immune responses to pathogens. IL10 polymorphisms have been associated with RHD, although results remain inconclusive. Our aim was to investigate the association between IL10 polymorphisms and RHD in Saudi Arabian patients. IL10 promoter polymorphisms (-1082A/G, -829C/T, and -592C/A) were genotyped in 118 RHD patients and 200 matched controls using the TaqMan allelic discrimination assay. There was a significant difference in IL10-1082 genotype frequency between patients and controls (p = 0.01). -1082G allele carriage (GG+GA vs AA) and the (-1082, -819, -592) GCC haplotype carriage were associated with an increased risk of RHD (p = 0.004, OR 2.1, 95% CIs 1.7-3.4 and p = 0.004, OR 2, 95% CIs 1.3-3.4, respectively). The ACC haplotype was associated with a decrease in RHD risk (p = 0.015, OR 0.6, 95% CIs 0.4-0.9). IL10 promoter polymorphisms may play an important role in the development of RHD and provide an opportunity for therapeutic stratification.

Autoimmunity in picornavirus infections

Enteroviruses are small, non-enveloped, positive-sense single-strand RNA viruses, and are ubiquitously found throughout the world. These viruses usually cause asymptomatic or mild febrile illnesses, but have a propensity to induce severe diseases including type 1 diabetes and pancreatitis, paralysis and neuroinflammatory disease, myocarditis, or hepatitis. This pathogenicity may result from induction of autoimmunity to organ-specific antigens. While enterovirus-triggered autoimmunity can arise from multiple mechanisms including antigenic mimicry and release of sequestered antigens, the recent demonstration of T cells expressing dual T cell receptors arising as a natural consequence of Theiler's virus infection is the first demonstration of this autoimmune mechanism.

Human autoimmune diseases: a comprehensive update

There have been significant advances in our understanding of human autoimmunity that have led to improvements in classification and diagnosis and, most importantly, research advances in new therapies. The importance of autoimmunity and the mechanisms that lead to clinical disease were first recognized about 50 years ago following the pioneering studies of Macfarlane Burnett and his Nobel Prize-winning hypothesis of the 'forbidden clone'. Such pioneering efforts led to a better understanding not only of autoimmunity, but also of lymphoid cell development, thymic education, apoptosis and deletion of autoreactive cells. Contemporary theories suggest that the development of an autoimmune disease requires a genetic predisposition and environmental factors that trigger the immune pathways that lead, ultimately, to tissue destruction. Despite extensive research, there are no genetic tools that can be used clinically to predict the risk of autoimmune disease. Indeed, the concordance of autoimmune disease in identical twins is 12-67%, highlighting not only a role for environmental factors, but also the potential importance of stochastic or epigenetic phenomena. On the other hand, the identification of cytokines and chemokines, and their cognate receptors, has led to novel therapies that block pathological inflammatory responses within the target organ and have greatly improved the therapeutic effect in patients with autoimmune disease, particularly rheumatoid arthritis. Further advances involving the use of multiplex platforms for diagnosis and identification of new therapeutic agents should lead to major breakthroughs within the next decade.

Geoepidemiological hints about Streptococcus pyogenes strains in relationship with acute rheumatic fever

Group A Streptococcus (GAS) strains are lately classified on the basis of sequence variations in the emm gene encoding the M protein, but despite the high number of distinct emm genotypes, the spectrum of phenotypes varying from invasive suppurative to non-suppurative GAS-related disorders has still to be defined. The relationship of GAS types with the uprising of acute rheumatic fever (ARF), a multisystemic disease caused by misdirected anti-GAS response in predisposed people, is also obscure. Studies published over the last 15 years were retrieved from PubMed using the keywords: "Streptococcus pyogenes" or "group A Streptococcus" and "acute rheumatic fever": the prevalence of peculiar emm types across different countries of the world is highly variable, depending on research designs, year of observation, country involved, patients' age, and gender. Most studies revealed that a relatively small number of specific emm/M protein types can be considered "rheumatogenic", as potentially characterized by the possibility of inducing ARF, with remarkable differences between developing and developed countries. The association between emm types and post-streptococcal manifestations is challenging, however surveillance of disease-causing variants in a specific community with high rate of ARF should be reinforced with the final goal of developing a potential primary prophylaxis against GAS infections.

Matrix-assisted laser desorption ionization-time of flight and comparative genomic analysis of M-18 group a Streptococcus strains associated with an acute rheumatic fever outbreak in northeast Italy in 2012 and 2013

Acute rheumatic fever (ARF) is a postsuppurative sequela caused by Streptococcus pyogenes infections affecting school-age children. We describe here the occurrence of an ARF outbreak that occurred in Bologna province, northeastern Italy, between November 2012 and May 2013. Molecular analysis revealed that ARF-related group A Streptococcus (GAS) strains belonged to the M-18 serotype, including subtypes emm18.29 and emm18.32. All M-18 GAS strains shared the same antigenic profile, including SpeA, SpeB, SpeC, SpeL, SpeM, and SmeZ. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis revealed that M-18 GAS strains grouped separately from other serotypes, suggesting a different S. pyogenes lineage. Single nucleotide polymorphisms and phylogenetic analysis based on whole-genome sequencing showed that emm18.29 and emm18.32 GAS strains clustered in two distinct groups, highlighting genetic variations between these subtypes. Comparative analysis revealed a similar genome architecture between emm18.29 and emm18.32 strains that differed from noninvasive emm18.0 strains. The major sources of differences between M-18 genomes were attributable to the prophage elements. Prophage regions contained several virulence factors that could have contributed to the pathogenic potential of emm18.29 and emm18.32 strains. Notably, phage ΦSPBO.1 carried erythrogenic toxin A gene (speA1) in six ARF-related M-18 GAS strains but not in emm18.0 strains. In addition, a phage-encoded hyaluronidase gene (hylP.2) presented different variants among M-18 GAS strains by showing internal deletions located in the α-helical and TSβH regions. In conclusion, our study yielded insights into the genome structure of M-18 GAS strains responsible for the ARF outbreak in Italy, thus expanding our knowledge of this serotype.