Amyloid P component is located on elastic fibre microfibrils in normal human tissue

Amyloid P component (AP) is a glycoprotein found in amyloid deposits1–3 which is apparently identical to the normal plasma protein, serum amyloid P component (SAP)4. SAP closely resembles C-reactive protein (CRP), the classical acute phase reactant, in molecular configuration5,6 and amino acid sequence7 but is not related to any other known protein. We have recently shown that a protein which is immunochemically cross-reactive with SAP is an integral constituent of normal human glomerular basement membrane and is covalently associated there with collagen and/or other matrix proteins8–10. We now report that antibodies to SAP bind immunospecifically to the peripheral, microfibrillar mantle of elastic fibres in the skin and in blood vessels of normal adults. These findings extend both biochemical characterization of elastic fibres, which are a universal and important constituent of connective tissues, and knowledge of the normal tissue distribution of AP.