An 8-year-old boy from the intermountain region of the United States is brought to the pediatrician with fever,rash,and pain in his knees and ankles.Pericarditis is evident on auscultation,and echocardiography confirms mitral valve regurgitation.Three weeks before this episode,the patient had experienced a sore throat but had not received medical attention.High titers of antistreptococcal antibodies are present in the serum.This child's disease is a result of which one of the following phenomena?
A)Clonal anergy
B)Peripheral tolerance
C)Epitope spreading
D)Central tolerance
E)Molecular mimicry

Question

Quizplus · Accepted Answer

This boy has acute rheumatic fever (ARF),which is caused by an immune response initially specific for streptococcal antigens,but that cross-reacts with heart antigens.Molecular mimicry refers to the postulated mechanism whereby immune responses to a microbe containing antigens that cross-react with self antigens may trigger an autoimmune response.This autoimmune response may then persist,even in the absence of the inciting microbe.In ARF,antistreptococcal antibodies cross-react with myocardial proteins.Molecular sequencing has revealed numerous short stretches of homologies between streptococcal protein and myocardial proteins.The incidence of ARF has declined dramatically in the United States because of widespread use of antibiotics in the treatment of streptococcal infections before antibody responses can fully develop.Clonal anergy,peripheral tolerance,and central tolerance are mechanisms that would prevent immune responses to self antigens,and thus do not explain this patient's disease.Epitope spreading occurs when autoimmune reactions develop against several different epitopes of self-molecules during the evolution of an autoimmune disease;these epitopes are different from the initial targets of autoreactive lymphocytes at the outset of the disease.Epitope spreading is due to the release of self antigens from damaged tissue and from activation of tissue-based antigen-presenting cells by the local inflammatory response.

An 8-Year-Old Boy from the Intermountain Region of the United