The relationship of a serum protein, C1t, to a common nonfibrillar constituent of amyloid (P component) as revealed by immunohistochemical studies.

C1t, a serum protein isolated by affinity chromatography on Sepharose bears a remarkable ultrastructural and physiocochemical resemblance to P component, a common constituent of amyloid. This study provides further evidence for their similarity by the demonstration of immunologic identity and by the presence of C1t in amyloid deposits of various types using immunoperoxidase and immunofluorescent techniques. In addition, subcomponents of C1, as well as C3, C4, C5, and properdin, were demonstrated to a limited extent. The possible role of C1t/P component in amyloidogenesis is discussed in the light of recent advances in our knowledge of the nature of amyloid substance.