Q.70 Rheumatic fever is an example of
(A) autoimmune disease (B) type IV hypersensitive reaction
(C) immunodeficiency disease (D) neurodegenerative disorder
Rheumatic fever is a post-infectious autoimmune condition triggered by group A streptococcal pharyngitis, making it a classic example of molecular mimicry in immunology. The correct answer to the MCQ is (A) autoimmune disease, as it involves the immune system attacking host tissues like heart valves due to cross-reactivity with bacterial antigens.
Correct Answer
Rheumatic fever (RF) follows untreated group A beta-hemolytic streptococcal throat infection by 2-3 weeks. Antibodies against streptococcal M proteins cross-react with human cardiac myosin, sarcolemma, and brain tissues via molecular mimicry, causing inflammation in joints, heart, skin, and CNS. This autoimmune pathogenesis distinguishes RF from direct infection, with genetic factors like HLA-DR2/DR4 increasing susceptibility.
Option Breakdown
| Option | Description | Why Correct/Incorrect |
|---|---|---|
| (A) Autoimmune disease | Immune response targets self-tissues (e.g., heart valves) post-streptococcal infection due to mimicry. | Correct. RF exemplifies type II hypersensitivity (antibody-mediated autoimmunity), leading to carditis, arthritis, and chorea. |
| (B) Type IV hypersensitive reaction | Delayed, cell-mediated immunity by T-cells (e.g., contact dermatitis, TB test). | Incorrect. RF is primarily type II (humoral, antibody-based), not type IV; T-cells play a secondary role in valve infiltration. |
| (C) Immunodeficiency disease | Impaired immunity increasing infection risk (e.g., SCID, AIDS). | Incorrect. RF stems from hyperactive, dysregulated immunity, not deficiency; affected individuals have normal baseline immunity. |
| (D) Neurodegenerative disorder | Progressive neuron loss (e.g., Alzheimer’s, Parkinson’s). | Incorrect. Sydenham’s chorea in RF is acute autoimmune neurology, reversible, not degenerative. |
Clinical Relevance
RF diagnosis uses Jones criteria (major: carditis, polyarthritis, chorea, erythema marginatum, nodules; minor: fever, arthralgia). Prevention relies on penicillin for strep pharyngitis, vital for students prepping molecular immunology or microbiology exams. Chronic rheumatic heart disease affects valves, underscoring early treatment in endemic areas like India.
