Tissue consisting of protein fibrils that may accumulate between cells in various animal tissues, especially in the disorder amyloidosis. Amyloid deposits are insoluble and can exert pressure on various vital organs. These deposits are generally detected by staining with the dye Congo red. In AL amyloidosis, abnormal plasma cells secrete excessive amounts of antibody proteins called light chains. These are present in the blood and accumulate in tissues, especially the kidney, where they aggregate to form fibrils. A build-up of amyloid tissue in the brain is also a feature of Alzheimer’s disease, Creutzfeldt-Jakob disease, and bovine spongiform encephalopathy.