In secondary amyloidosis the fibrils deposited in tissues are unrelated to immunoglobulin light chains (in contrast to the situation in primary amyloidosis) and are made of amyloid A protein (AA protein). This is derived from serum amyloid A (SAA) that is the apolipoprotein of a high density lipoprotein and an acute phase protein. Partial proteolysis converts SAA into the pleated sheet configuration of the amyloid fibrils. Amyloid p protein is also found as a minor component of the fibrils (in both primary and secondary amyloidosis) and is derived from serum amyloid P that has similarity to c-reactive protein. The physiological role remains obscure.