[Amyloidosis. I. Recent findings concerning amyloid substance]

The considerable progress made recently in the study of amyloid substance have led to the identification of numerous organised protein components in typical microfibrillar structures. In spite of the biochemical heterogeneity of fibril proteins, it is still possible to find similar chemicophysical and tintorial features in the various types of amyloid, probably due, at least in part, to the common Beta type molecular configuration, a structure proper to fibril proteins. In so-called primary amyloidosis and in that associated with myelomatous diseases, the principal protein component consists of AL protein, correlated with the light immunoglobulin chains, with which analogies have been observed both in the amino acid sequence and in antigenic characteristics. In secondary amyloidosis, AA protein, which is unrelated to immunoglobulins or other known human proteins, is prevalent. AA protein probably derives from a serum globulin, SAA, whose blood levels increase during numerous pathological processes, particularly in those of neoplastic or inflammatory type. The origin of serum protein, which might be either a normal tissue component released under stimulus or a reagent of the acute phase synthesised ex novo, and its function, which is probably of immunomodulator or more specifically immunosuppressive type, are still to be defined. In all forms of amyloidosis studied, a common observation is the presence of AP protein, organised in pentagonal structures. This protein would appear to derive from a serum component defined as SAP, with a marked affinity for amyloid fibrils. Also identifiable are other forms of amyloid such as APUD-amyloid, which probably derives from polypeptide hormones, and AS amyloid, which is present in some organs of elderly patients and is biochemically identifiable at cardiac level with A(SCA) protein. Still awaiting definition in amyloid tumours or amyloidomas is the precise chemical composition of deposited proteins.