RHEUMATIC FEVER - aetiology & immunopathogenesis

1. RHEUMATIC FEVER - aetiology & immunopathogenesis Dr SandeepMohanan Department of Cardiology, Calicut Medical College

2. OVERVIEW - HISTORY - EPIDEMIOLOGY - AETIOLOGY - IMMUNOPATHOGENESIS - PATHOLOGY

3. INTRODUCTION • Rheumatic fever is a non-suppurative complication of Streptococcal infection. • Most common cause of acquired cardiac disease in children & young adults • Annually ~4,70,000 cases of rheumatic fever worldwide ( Moss& Adams)

4. HISTORY • Known to exist as early as the 17th century • Chorea was related to arthritis by Sydenham in 1600s. • Charles Wells (1812)– Association of rheumatism with carditis and subcutaneous nodules • Jean –BaptisteBouillaud (1836) – 1st publication on rheumatic fever (‘Father of rheumatic heart disease’)

5. Jean-BaptisteBouillaud

6. Association of ARF with pharyngitis was noted in 1880 • Walter B Cheadle (1889)– 1st classic description of rheumatic fever. • Ludwig Achoff(1904) - 1st description of pathology of rheumatic carditis.

7. Ludwig Aschoff • Aschoff-Tawara node • Aschoff-Rokitansky sinuses

8. Alvin F Coburn (1931) – 1st proved causal relationship between Beta hemolytic Strep and ARF Alvin F. Coburn.THE SIGNIFICANCE OF PROLONGED STREPTOCOCCAL ANTIBODY DEVELOPMENT IN RHEUMATIC FEVER. J Clin Invest. 1939 January; 18(1): 141–145.

9. Rebecca Lancefield (1933) – Serogrouping of Streptococci • T Duckett Jones (1944) – 1st diagnostic criteria for RF He presented his paper on the diagnosis of rheumatic fever in Chicago (AMA meeting)

10. EPIDEMIOLOGY OF RF • Incidence in developed countries ~ 0.5-3/100,000 • Incidence in developing countries – as high as~ 100-200/100,000 • Overall mean incidence of RF worldwide : 5-50/100,000 (Tibazarwa et al. Incidence of acute rheumatic f ever in the world: a systemic review of population-based studies. Heart2008; 94:1534-40) - India – 25-50% of global burden of RHD (WHO statistics 2002) - India – 0.2-0.75/1000/year in school children and around 1/3rd develop RHD. (Grover et al. Burden of rheumatic and congenital heart disease. Indian Heart J 2002; 54: 104-7) • Recent ICMR registry study, prevalence of RF – 0.0007 to 0.2/1000 in urban population.

11. RF worldwide incidence

12. RF worldwide incidence recent trends However recent data from India can not be conclusively relied upon to suggest a definite declining trend, due to the fallacies in epidemiological studies.

13. Prevalence of RHD in India-declining trend? Prevalence of rheumatic heart disease: Has it declined in India? S. RAMAKRISHNAN, et al. National Medical Journal of India , 2009.

14. The downtrend of rheumatic fever incidence has however led to decline in the global interest for further research on its genetic and immuno-pathogenic basis. • Thus even now after >70 years of its first etio-pathological explanation, the actual immune basis for the development of rheumatic carditis is still an unsolved mystery.

15. AETIOLOGY • Alvin F Coburn in 1931 1st proved the association between Streptococcus pyogenes and RF • Other agents that have been explored and linked to RF are HSV-1, Coxsackie B & Measles virus. However they all remained unproven hypothesis.

16. THE ‘GAS’ • Streptococcus pyogenes • Gram positive cocci • 1µm in diameter • Chains or pairs • Usually capsulated • Non motile • Non spore forming • Facultative anaerobes • Catalase negative (Staphylococci are catalase positive)

17. Lancefield’s serological Classification • Streptococci classified into many groups from A-K & H-V • One or more species per group • Classification based on C- carbohydrate antigen of cell wall • Groupable streptococci • A, B and D (more frequent) • C, G and F (Less frequent) • Non-groupablestreptococci • S. pneumoniae (pneumonia) • S. viridans species • e.g. S. mutans

18. Classification of Streptococci Based on Hemolysis on Sheep blood Agar • Hemolysis on BA • -hemolysis • Partial hemolysis • Green discoloration around the colonies • e.g. non-groupable streptococci (S. pneumoniae & S. viridans) • -hemolysis • Complete hemolysis • Clear zone of hemolysis around the colonies • e.g.Group A & B (S. pyogenes & S. agalactiae) • -hemolysis • No lysis • e.g. Group D (Enterococcusspp) -hemolysis -hemolysis -hemolysis

20. Diagrammatic structure of the group A beta hemolytic streptococcus Capsule Cell wall Protein antigens Group carbohydrate Peptidoglycan Cyto.membrane Cytoplasm …………………………………………………...

21. Pathogenic and Virulence Factors • Structural components • M protein • Lipoteichoicacid • F protein for cell adhesion • Hyaluronic acid capsule-- which acts to camouflage the bacteria • Enzymes (facilitate the spread of bacteria in tissues) • Streptokinases • Deoxynucleases • C5a peptidase • Pyrogenic toxins-- stimulate macrophages and helper T cells to release cytokines • Streptolysins • Streptolysin O lyse red blood cells, white blood cells, and platelets • Streptolysin S

22. M protein - Major surface antigen (T,R) - Rebecca Lancefield in 1962 - ‘Emm’ gene - Resistance to phagocytosis - Has epitopes causing cross-reactivity with myocardium, synovia, skin & brain. • > 130 M serotypes

23. Alpha helical coiled-coil fibrillar protein– significant homology in structure & a.a sequences to tropomyosin, myosin, keratin, vimentin & laminin. • It has a hypervariable NH2- terminal and a conserved C-terminal. • The NH2- terminal is responsible for the formation of opsono-phagocytic Abs after around 2 weeks of infection. • The body is divided into A, B and C repeats based on the peptide sequence periodicity. • The B repeat region is the immunodominant region and elicit an exaggerated immune response(B cell)– however this is not opsonic.

24. The C repeat region is considered to have conserved T cell epitopes that also elicit tissue specific immune response • ( basis for RF-vaccine research) • Based on the conserved C repeat regions Class I & Class II GAS strains are named. • It is the Class I M-type of which belongs the strains 1,3,5,6,14,18,19 and 24 ---that have been associated with RF • The Class II strains have non-reactive M-types. • The important cross-reactive epitopes are distributed between the B & C repeats of the M-protein.

25. Cross reactivity of M protein is related to structural as well as sequential homology – 30-40% • Antiphagocytic properties are cause by specific inhibitory effects on alternative complement pathway (Factor H affinity mediated inhibition) • M protein also promote streptococcal adherence • M proteins exhibit antigenic variation through intragenic recombination– causing varying lengths of the a.a sequence -- This hampers the formation of broad non-type specific immunity to counter against reinfection from different strains of GAS. -- this variation in strains have also hampered the development of a vaccine based on M protein.

26. Probable Streptococcal vaccines

27. Streptococcal pharyngitis • ~15-20% of pharyngitisin children 5- 15 years. • Most common is Group A – ~60% especially in temperate countries • Group C and G also form a good majority in tropical countries (not related RF) • Carrier state does not mean infection and is not clinically relevant ( maybe epidemiologically relevant) • Infection itself maybe asymptomatic in up to 30-50% cases of RF. • Infection is defined as a rising trend in antibody titres • Secondary infection is primarily determined by socioeconomic and environmental factors.

28. Streptococcal pharyngitis (contd) • IP- 2-4 days • Sudden onset • Severe odynophagia • Rhinitis, Laryngitis and bronchitis are not features • Fever, headache, vomiting and abdominal pain • Characteristic physical findings • Penicillin treatment may not alter the duration of illness.

29. RF following GAS pharyngitis • Latent period of 1 to 5 weeks ( 18 days) • 0.3-3% • -Rheumatogenic M serotypes : 1,3,5,6, 14,18,19, 24, 27,29 ( 2, 4, 12, 22 and 28- unlikely to cause RF) • Virulence of the particular strains • Encapsulation & formation of mucoid colonies • Anti-Streptococcal host-immune response • RF following skin infections with GAS have been reported in the aborginal tribes of Australia.

30. PATHOGENESIS ? DIRECT INFECTION ?STREPTOCOCAL TOXIN AUTOIMMUNITY – ANTIGENIC MIMICRY ? AUTOIMMUNITY

32. THE CONDUCIVE ‘ENVIRONMENT’ • Overcrowding • Poverty • Poor nutrition • Poor hygiene • Poor access to health care • Rapid spread • Lack of primary prevention • Lack of secondary prevention INDIA

33. Changes in ‘environmental factors’ with time

34. GAS VIRULENCE Virulent clones may change in a cyclical manner with time. These result in epidemics such as the one that occurred in USA in the early 1990s.

35. HOST RESPONSE - IMMUNITY • The exact immune reaction that occurs to a preceding GAS infection is yet to be elucidated. • However there have been several postulates of which “MOLECULAR MIMICRY” is presently considered to be involved. • Stollerman et al (1960) 1st noted the relation between RF and certain rheumatogenic M-type strains of GAS infection. • Kaplan et al(1965) was the first to postulate molecular mimicry as the cause of RF by demonstrating Igs and complement bound to cardiac tissue (in the absence of bacteria) following streptococcal infection.

36. IMMUNOPATHOGENESIS • Mechanisms involved: • ?Molecular Mimicry (? M-protein , ? Carbohydrate antigen) -- Direct relationship not proven yet • ?Super-antigens • ?Genetic susceptibility for development of ‘forbidden clones’ • Causative antigen is yet to be conclusively identified!! ( Humans are the only natural hosts for GAS and experiments have failed to develop an appropriate animal model)

38. MOLECULAR MIMICRY • “Sharing of epitopes between host tissue and bacterial antigens” - Antibody (B cell) mediated: 1) Recognition of aminoacid sequences 2) Recognition of homologous non-identical a.a sequences 3) Recognition of epitopes on different molecules - Cell mediated (T cell) : 1) By antigen presentation to TCR 2) Epitope spreading (i.e T cells recognize epitopes in other proteins with equal or more priority than the original bacterial epitope)

39. Ab mediated injury • Antibodies and complement mediated injury were conclusively demonstrated in cardiac tissues by 1970. • Earlier studies pointed towards ?M protein and group A carbohydrate (N-acetyl glucosamine) as the antigens. • Priliminary studies using monoclonal Abs suggested ? myosin as the dominant autoantigen. • Other autoantigens against which mimicry was identified were vimentin, tropomyosin, keratin and laminin. (Laminin- An ECM protein that secreted by endothelial cells and lines the heart valves) • Gln-Lys-Ser-Lys-Glnwas identified as an epitope on the M protein which cross reacted with Abs in the sera. • Ab mediated injury is presumed as the initiator of cardiac injury.

40. T cell mediated injury • Involves T cell mediated ‘mimicry’ and epitope spreading. • Ab s also activate T cells which in turn initiate inflammatory response . • Recent studies show that T cells specifically recognize an epitope on the M protein - M5(81-96) epitope presented to the TCR by HLADR53. • Typically a TH1 response is initiated. • They produce the cytokines - IFN-gamma, IL-1 and TNF-alpha in valves, pericardium and myocardium. • IL4 ( an immune-regulator cytokine) is found in only small quantities in rheumatic valvulitis explaining the persistence and perpetuation of valvular inflammation.. Fae et al.How an autoimmune reaction triggered by molecular mimicry between streptococcal M protein and cardiac tissue proteins leads to heart lesions in rheumatic heart disease.JAutoimmun. 2005 Mar;24(2):101-9.

41. Immunopathogenesis of rheumatic valvulitis • A 2 stage process: Auto-Abs home in, damage and inflame the valve endothelium (? Laminin) Complement mediated injury takes over Upregulation of VCAM-1 occurs on endothelial surface T cell mediated extensive injury and tissue infiltration via VCAM-1 (Epitope spreading – vimentin, myosin, ? Ags on VICs) CD4+ TH1 mediated granulomatous inflammation IFN gamma and TNF alpha mediated fibrosis, Low IL4 production Neovascularization, persistence of inflammation & scarring

42. Rheumatic valvulitis

43. Rhematicvalvulitis

44. Genetic susceptibility to RF - Familial tendency for RF had been investigated but no conclusive pattern of inheritance could be elucidated. - HLA-II (Chr 6) is the gene most associated with RF and development of RHD - HLA-DR7 mostly associated with progressive valvular lesions in RHD - HLA-DR53, HLA-DQA, HLA-DR4, HLA-DR9 (determines antigen presentation to T-cell receptors) - TNF alpha alleles also associated - Non HLA B cell antigen D8/17 is associated with increased susceptibility - In a recent metanalysis that quantitated the genetic susceptibility of RF it was found that the concordance in monozygotic twins was 44% and in dizygotic twins 12% and the overall estimated heritability was 60% (Engel et al. Genetic Susceptibility to Acute Rheumatic Fever: A Systematic Review and Meta-Analysis of Twin Studies. Plos-one, 2011.)

45. RF HLA class II susceptibility worldwide

46. Valve +/- Myocardium ? - Our present knowledge of the pathology reveals that RF primarily involves mesothelial and endothelial tissues. -The cardiac valves are basically an extension of the A-V sulcus region formed by a process called ‘undermining’, which excludes the myocardium. - The valve loses its muscle component and becomes a core of connective tissue sandwiched between 2 layers of endothelium. • Even though “myosin” was previously thought as the main causative antigen – currently there is enough evidence on the fact that valves are targeted by priority... Rather than the myocardium.

47. Pancarditis- a misnomer? • Myocarditis presumed on the basis of finding interstitial inflammation and Aschoff bodies. • No definite evidence of myocarditis!! - No consistent elevation of cardiac biomarkers - No evidence of loss of cardiac contractility - CHF does not occur without significant valvular lesions - Radionuclide studies (Tc pyrophosphate, antimyosinfab, indium labelled myosin etc ) failed to demonstrate significant myocardial staining - Biopsy in acute RF failed to show cellular necrosis (Narula et al)--- inflammation was subepicardial, subendocardial and perivascular - Surgical valve replacement during RF and AHF reverted features of heart failure. - Aschoff nodules do not contain myocardial cells. === Thus evidence points against the theory that molecular mimicry to myosin/tropomyosin is central to the pathogenesis!!!

48. An Endothelial disease

49. - Endothelial diseases tend to focal. - They are usually transient due to the high regenerative capacity....however chronic and recurrent endothelial insults may result in subendothelial and connectuve tissue fibrosis. - Explains the transient manifestations of Rheumatic fever and chronic involvement of valves Conclusion: Cross-reacting Ags – M protein +/- Carbohydrate Self-Antigens - Laminin, VICs, Vimentin> >Myosin

50. SUPERANTIGENS • A possible mechanism that may contribute to the systemic inflammation. • They are glycoproteins found on bacterial cell wall that promote the binding of MHC Class II with TCRs --- thus inciting T-cell activation and release of cytotoxins. • Streptococcal pyrogenexotoxin– a possible culprit • May explain the systemic inflammatory changes