Rheumatic fever pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Lance Christiansen, D.O.; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Pathophysiology
Rheumatic fever is a systemic disease affecting the peri-arteriolar connective tissue and can occur after an untreated Group A streptococcal pharyngeal infection. It is believed to be caused by antibody cross-reactivity. This cross-reactivity is a Type II hypersensitivity reaction and is termed molecular mimicry.
Usually, self reactive B cells remain anergic in the periphery without T cell co-stimulation. During a Strep. infection activated antigen presenting cells such as macrophages present the bacterial antigen to helper T cells. Helper T cells subsequently activate B cells and induce the production of antibodies against the cell wall of Streptococcus. However the antibodies may also react against the myocardium and joints[1], producing the symptoms of Rheumatic fever.
Group A streptococcus pyogenes has a cell wall composed of branched polymers which sometimes contain "M proteins" that are highly antigenic. The antibodies which the immune system generates against the "M proteins" may cross react with cardiac myofiber sarcolemma and smooth muscle cells of arteries, inducing cytokine release and tissue destruction. This inflammation occurs through direct attachment of complement and Fc receptor-mediated recruitment of neutrophils and macrophages. Characteristic Aschoff bodies, composed of swollen eosinophilic collagen surrounded by lymphocytes and macrophages can be seen on light microscopy. The larger macrophages may become Aschoff giant cells. Acute rheumatic valvular lesions may also involve a cell-mediated immunity reaction as these lesions predominantly contain T-helper cells and macrophages.[2]
In acute RF, these lesions can be found in any layer of the heart and is hence called pancarditis. The inflammation may cause a serofibrinous pericardial exudates described as “bread-and-butter” pericarditis, which usually resolves without sequelae. Involvement of the endocardium typically results in fibrinoid necrosis and verrucae formation along the lines of closure of the left-sided heart valves. Warty projections arise from the deposition, while subendothelial lesions may induce irregular thickenings called MacCallum plaques.
Chronic rheumatic heart disease is characterized by repeated inflammation with fibrinous resolution. The cardinal anatomic changes of the valve include leaflet thickening, commissural fusion and shortening and thickening of the tendinous cords. RHD cause 99% of mitral stenosis often resulting in a “fish mouth” gross appearance.[3]
References
- ↑ Abbas and Lechtman. mBasic Immunology: Functions and Disorders of the Immune System. Elsevier Inc. 2004.
- ↑ Kumar et al. Robbins and Cotran Pathologic Basis of Disease. Elsevier Inc. 2005
- ↑ "Robbins & Cotran Pathologic Basis of Disease".