Lung - Amyloid

Amyloid (Figure 1, Figure 2, Figure 3, and Figure 4) refers to insoluble, extracellular and/or intracellular proteins that appear as amorphous, eosinophilic, acellular material histologically. It stains positively with Congo red stain and has a characteristic apple green birefringence under polarized light. Deposition of amyloid can be focal, multifocal, or diffuse. Involvement of vascular walls is not uncommon, but it may also be seen in peribronchial areas. In severe cases, the pulmonary parenchyma may be effaced. Approximately 90% of the deposits consist of amyloid fibrils formed by the aggregation of misfolded proteins, and 10% of the deposits consist of glycosaminoglycans, apolipoprotein E, and serum amyloid P. Amyloidosis is found as a background change in some strains, such as CD-1 mice. Pulmonary amyloidosis is a spontaneous lesion in aging rodents and may be localized to the lung, or it may be a component of systemic amyloidosis involving spleen, kidney, liver, and other organs. It may also be associated with chronic inflammation. Since an association between amyloid deposition in the lung and xenobiotic administration has not been reported, amyloid deposition is generally considered a background finding. It may, however, be the cause of morbidity or mortality in some animals and can affect the outcome of a study.