Primary (AL) amyloidosis has precursor protein derived from immunoglobulin light chains. Secondary (AA) amyloidosis has precursor protein serum amyloid A (SAA), an acute phase reactant. In AA amyloidosis, SAA is converted to amyloid A (AA) fibrils in which organ?

• A Kidney — tubular epithelial cells process SAA into fibrils
• B Spleen — splenic macrophages exclusively generate AA fibrils
• C Bone marrow — plasma cells directly produce AA protein
• D Liver and macrophages — SAA cleaved by macrophage enzymes to form AA fibrils ✓

Explanation

SAA is an apolipoprotein synthesized predominantly by the liver as an acute phase reactant, transported bound to HDL. Macrophages (monocytes/macrophage system) process SAA by incomplete proteolysis, generating AA fragments that misfold into beta-pleated sheet fibrils. Fibril formation is also influenced by serum amyloid P component (SAP) and proteoglycans. The kidney, liver, and spleen are the major organs involved in AA deposition (not generators). Plasma cells produce immunoglobulin light chains (AL amyloid), not AA protein.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.