[Amyloid P components in normal human skin and skin with lesions]

Amyloid P component (AP) is a glycoprotein which is found in tissue deposits of all types of amyloid and is identical to and derived from serum amyloid P component (SAP). SAP binds in a calcium-dependent fashion to various ligands, such as agarose, desoxyribonucleic acid, fibronectin, C4-binding protein, glycosaminoglycans and isolated amyloid fibrils. Tissue AP (TAP) is also a constituent of the normal human renal glomerular basement membrane and is, in adult humans, invariably associated with elastic fiber microfibrils in connective tissue throughout the body, including that of blood vessels. In normal human skin anti-AP antibody binding was localized to the microfibrils of oxytalan fibers in the papillary dermis and to the peripheral microfibrillar mantle of elaunin and mature elastic fibers in the reticular dermis. Since SAP binds to fibronectin and glycosaminoglycans, which in turn bind to collagen fibers, TAP on elastic fiber microfibrils may play an important role in the maintenance of the normal dermal architecture and in dermo-epidermal adhesion. Under pathological conditions, AP is found in all forms of cutaneous amyloidosis, including primary localized cutaneous amyloid (PLCA); it is also detectable on keratin bodies, which represent precursor structures for PLCA. The association of AP with elastic fiber microfibrils and amyloid fibrils and their close anatomical relationship in vivo may reflect the significance of AP in the deposition of cutaneous amyloid.