Role of altered vascular permeability amyloid formation.

Heavily radiolabeled plasma proteins were injected intravenously into mice with experimentally induced amyloid lesions, and the distribution of the labeled protein with respect to vascular spaces and the amyloid lesions determined by autoradiography. Radiolabeled albumin and IgG entered early amyloid lesions so quickly and in such high concentration as to indicate that much of the volume of these early lesions must be occupied by circulating plasma. Entry of these same proteins into advanced lesions was definitely reduced. High-molecular-weight proteins remained largely in vascular spaces. In situ saline perfusion resulted in considerable removal of protein from early lesions but very little alteration in their greenish-yellow birefringence when stained with Congo red. An initial alteration in vascular permeability with circulation of plasma proteins in tissue spaces quickly followed by a progressively increasing deposition of fibrous proteins on an underlying cellular framework may be the sequence of events in amyloid formation.