Extracellularly stored glycoproteins characterized by common staining, biochemical and ultrastructural properties, see also amyloidosis. Amyloid is a "waste product" that can hardly be taken up and degraded by macrophages. It differs from all other human proteins and consists for the most part of unbranched, rigid fibrils (see below) whose polypeptide chains mostly have a beta-sheet structure. All amyloid types contain a non-fibrillar component derived from the physiological serum component serum-alpha-globulin (SAP) as well as glycosaminoglycans. Different proteins, e.g. keratin, immunoglobulins, insulin and beta2-microglobulin can be deposited as amyloid.
- In HE section: Amorphous, eosinophilic, homogeneous material.
- In Congo red stain: metachromasia.
- In polarized light: green glow.
- In fluorescence microscopy: Yellow brightening after thioflavin T staining.
- Ultrastructural: Linear unbranched fibrils with a diameter of 7.5 to 10 nm.
In addition to the fibrillar component, 10% of amyloid consists of a non-fibrillar substance, the so-called P-component.