In systemic amyloidosis (AA type), the serum precursor protein that deposits as amyloid fibrils is derived from which acute-phase reactant?

• A Serum amyloid A (SAA), an apolipoprotein produced by the liver under IL-6 stimulation ✓
• B Immunoglobulin light chains (AL amyloid), produced by plasma cell dyscrasia
• C Transthyretin (ATTR), produced by hepatocytes and choroid plexus
• D Beta-2 microglobulin, shed from MHC class I complexes during dialysis

Explanation

AA amyloidosis (secondary or reactive amyloidosis) occurs in chronic inflammatory conditions (RA, IBD, osteomyelitis, tuberculosis). The precursor protein is serum amyloid A (SAA), an apolipoprotein synthesised by the liver as a major acute-phase protein in response to IL-1, IL-6, and TNF-alpha. SAA is incompletely degraded by macrophage proteases, and resistant fragments polymerise into amyloid A (AA) fibrils. AL amyloid is derived from immunoglobulin light chains in plasma cell dyscrasias. ATTR causes familial and senile cardiac amyloidosis. Beta-2 microglobulin causes dialysis-related amyloidosis.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.