Regarding the histopathology and immunopathogenesis of acute rheumatic fever (ARF) and rheumatic heart disease (RHD), all of the following statements are correct EXCEPT:

Explanation

## Histopathology and Immunopathogenesis of Acute Rheumatic Fever ### Aschoff Bodies: Location and Distribution **Key Point:** Aschoff bodies are granulomatous lesions found in ALL three layers of the heart — myocardium, endocardium, and pericardium. They are NOT exclusive to the myocardium. | Layer | Involvement | Lesion Type | | --- | --- | --- | | Myocardium | Yes | Aschoff bodies, inflammation | | Endocardium | Yes | Aschoff bodies, verrucous vegetations | | Pericardium | Yes | Aschoff bodies, fibrinous pericarditis | ### Histological Features of Acute Rheumatic Carditis 1. **Aschoff Bodies** — central fibrinoid necrosis surrounded by: - Anitschkow cells (activated macrophages with central wavy ribbon of chromatin — "caterpillar cells") - Aschoff giant cells (multinucleated cells derived from Anitschkow cells) - Lymphocytes and plasma cells 2. **Anitschkow Cells** — characteristic but NOT pathognomonic (also seen in other granulomatous conditions and chronic inflammation). 3. **Verrucous Vegetations** — small sterile vegetations along the lines of valve closure, seen on endocardium. **High-Yield:** Aschoff bodies are the hallmark of ARF but are NOT pathognomonic — they can be seen in other conditions. However, they are the MOST specific lesion for ARF. ### Immunopathogenesis of ARF/RHD **Mnemonic: MMCD** — Molecular Mimicry, Macrophages, CD4+ T cells, Delayed hypersensitivity 1. **Molecular Mimicry** — streptococcal M protein shares epitopes with cardiac myosin, tropomyosin, and other cardiac antigens; cross-reactive antibodies and T cells attack cardiac tissue. 2. **CD4+ T Cell Response** — Th1 and Th17 cells drive inflammation; CD4+ T cells are central to the pathogenesis. 3. **B Cell Response** — anti-streptococcal antibodies cross-react with cardiac antigens; produces anti-heart antibodies. 4. **Macrophage Infiltration** — activated macrophages form Anitschkow cells and Aschoff giant cells. **Clinical Pearl:** The latency period (2–3 weeks between streptococcal infection and ARF onset) reflects the time needed for adaptive immune responses and cross-reactive antibody production. ### Why Option 2 is Correct Aschoff bodies are found in the myocardium, endocardium, AND pericardium — NOT exclusively in the myocardium. This statement is **FALSE** and is the correct answer to the EXCEPT question. [cite:Robbins 10e Ch 12]