Amyloid precursors and amyloidosis in rheumatoid arthritis

Amyloidosis refers to the extracellular accumulation of amyloid fibrils, de rived from a circulating precursor, in various tissue and organs. The most common form of amyloidosis worldwide is that which occurs secondary to chro nic inflammatory disease, particularly rheumatoid arthritis. The precursor molecule is serum amyloid A (SAA), an acute phase reactant, which can be us ed as a surrogate marker of inflammation in many diseases. SAA has a number of immunomodulatory roles, can induce chemotaxis and adhesion molecule exp ression, has cytokine-like properties and can promote the upregulation of m etalloproteinases. It enhances the binding of high density lipoprotein to m acrophages and thus helps in the delivery of lipids to sites of injury for use in tissue repair. It is thus thought to be an integral part of the dise ase process. Moreover, elevated levels of SAA over time predispose to secon dary amyloidosis. Pathogenic factors underlying this disease are outlined a long with guidelines for diagnosis and management.