A 63-year-old man has had chronic arthritis for the past 15 years. Physical examination shows ulnar deviation with bony ankylosis producing swan neck deformities of the fingers. Laboratory studies show 4.2 g of protein in a 24-hour urine collection, serum creatinine of 3.1 g/ dL, and urea nitrogen of 3 g/dL. Level of C-reactive protein is markedly elevated. A rectal biopsy is performed, which shows deposition of amorphous pink material with H&E staining in the mucosa. The material stains positive with Congo red. Which of the following proteins is the most likely precursor to this material in the mucosa?
Acute-phase reactant
b2-Microglobulin
g light chains
Transthyretin
In chronic inflammatory conditions such as rheumatoid arthritis, the serum amyloid-associated (SAA) precursor protein forms the major amyloid fibril protein AA. SAA is an acute phase reactant that increases with inflammatory conditions. C-reactive protein also is an acute phase reactant whose level is increased in inflammatory conditions; unlike SAA, however, this does not form amyloid. Amyloid is deposited in interstitial locations. All amyloid shows characteristic "apple- green" birefringence under polarized light microscopy after Congo red staining-anything else would not be amyloid. Amyloid derived from b2 -microglobulin occurs with hemodialysis-associated amyloidosis. Amyloid derived from light chains in association with multiple myeloma has AL fibrils. Cardiac and heredofamilial forms of amyloidosis have fibrils derived from prealbumin transthyretin (TTR).
Immunity