Adult male rhesus macaque, (Macaca mulatta).This animal was euthanized for research purposes.
Postmortem examination revealed an adult male rhesus macaque in good body condition with excess subcutaneous and mesenteric adipose stores.Â The liver was markedly enlarged, friable, and mottled dark brown, olive, and pale yellow.Â Sections of liver were submitted in 10% neutral buffered formalin and post-fixed in 2.5% glutaraldehyde for transmission electron microscopy.
Electron Microscopic Description:
This electron micrograph contains portions of 5 large polygonal cells, 4 of which converge to form a 2 Î¼m diameter channel lined by a microvillous brush border (bile canaliculus).Â The cell in the center of the image is 22 Î¼m in greatest dimension and contains abundant, medium-electron dense, bland cytoplasm, and 2 round nuclei with prominent nucleoli and peripherally condensed heterochromatin (binucleate hepatocyte).Â The cells are bordered by a 15 Î¼m wide branching sinusoid which is filled with large numbers of densely packed, pale, randomly-oriented and interlacing, non-branching, ~10nm diameter fibrils (amyloid).Â
This electron micrograph contains 2 distinct types of extracellular fibrillar material.Â Centrally there is a 3 Î¼m wide bundle of ~50nm diameter, banded fibrils arranged in regular parallel arrays (collagen).Â Above and below the collagen bundle, there are large numbers of densely packed, medium-electron dense, randomly-oriented and interlacing, non-branching, ~10nm diameter fibrils (amyloid).Â A small portion of a cell is visible at the bottom of the image.Â
Liver: Amyloidosis, sinusoidal, with focal fibrosis.
Amyloid is an extracellular proteinaceous material composed of approximately 95% fibrillar proteins, and 5% amyloid P protein, proteoglycans, and glycosaminoglycans.(12) Conformationally, the fibrils form regular arrays of Î²-pleated sheets which allows for positive Congo Red staining and a characteristic green birefringence when viewed under polarized light.(12) Numerous biochemical forms of amyloid have been identified.Â The amyloid light chain (AL) form is composed of intact or fragmented immunoglobulin light chains, and is associated with immune cell dyscrasias (primary amyloidosis).(12) The amyloid-associated (AA) form is derived from the acute phase protein, serum amyloid A, and is associated with chronic inflammation (secondary amyloidosis).(12) Other commonly recognized types include AÎ² amyloid and islet amyloid, which are associated with cerebral amyloid angiopathy of Alzheimers disease, and Type II diabetes mellitus, respectively.(15,16)
Amyloidosis is the pathologic accumulation of amyloid in tissues and can be systemic or localized.Â It has been identified in mammals, reptiles, and birds and is a well-recognized condition in rhesus monkeys and other macaques.(1,7,8,17)
By light microscopy, amyloid has a homogenous eosinophilic hyaline appearance which can be similar to other extracellular fibrillar proteinaceous deposits, such as collagen or fibrin.Â Ultrastructurally, however, it has a distinct appearance and can be readily differentiated, as seen in this case.Â When viewed with transmission electron microscopy, amyloid fibrils are non-branching, 7.5-10nm in diameter, and randomly-oriented and interlacing.(3) This is in contrast to collagen which has larger fibrils (~50nm in diameter) that are banded and arranged in regular parallel arrays; and fibrin, the strands of which vary in diameter and form dense irregularly-branching mats, generally in the vicinity of platelets.(4,5)
Liver, space of Disse: Amyloidosis with hepatocellular compression.
Amyloidogenic proteins have a tendency toward misfolding which leads to the formation of unstable, self-associated fibrils.(12) Reactive systemic (secondary) amyloidosis is the most common form of amyloidosis in domestic animals.Â Tissue accumulations is caused by overproduction of AA amyloid, in combination with reduced destruction, and is often associated with chronic inflammatory or neoplastic diseases.(7,9) The precursor to AA, serum amyloid A (SAA), is an acute phase protein produced by the liver during inflammatory conditions under the influence of IL-6 and IL-1.Â SAA is normally degraded by the monocyte-macrophage system,(12,13) however, a prolonged increase in SAA alone is not sufficient to induce amyloidosis.Â Several explanations for the development of reactive amyloidosis have been proposed, including a defective SAA degradation system and an inherent alteration in quality of SAA, which renders it resistant to complete degradation.(12)
Systemic AA amyloidosis can also be inherited in humans (familial Mediterranean fever), Chinese Shar-Pei dogs (autosomal recessive Familial AA amyloidosis), Abyssinians (autosomal dominant with incomplete penetrance) and Siamese cats.Â In Shar-Peis with inherited amyloidosis, amyloid is preferentially deposited in the renal medullary interstitium, while in Abyssinian cats, deposition is glomerular and in Siamese cats amyloid deposits accumulate in the hepatic space of Disse.Â Whether reactive or inherited, clinical signs in systemic amyloidosis are generally secondary to dysfunction of adjacent organs and pressure atrophy in areas adjacent to amyloid accumulation.(12,13)
In dogs, AA amyloidosis is usually idiopathic, but it has also been associated with Hepatozoon americanum, Ehrlichia can is and other causes of chronic suppurative/granulomatous inflammation.Â Canine AA amyloidosis lesions usually occur within renal glomeruli, which leads to proteinuria and progressive renal insufficiency.(13) In contrast, feline amyloidosis primarily affects the renal medulla, so proteinuria is not a typical clinical finding.(13) Equine systemic AA amyloidosis is a well-recognized hepatic lesion in horses used to produce hyperimmune serum.(13) Glomerular amyloidosis, with accompanying proteinuria, occurs occasionally in ruminants.Â Swine rarely develop amyloidosis.(13) Much like the other forms of reactive amyloidosis described above, avian amyloidosis tends to develop after a period of chronic inflammation and occurs most frequently in waterfowl, although it has also been reported in chickens (amyloid arthropathy).(9) Conversely, reactive amyloidosis is rarely reported in reptiles (snakes and tortoises).(17)
Reactive amyloidosis has been described in the Patas monkey, squirrel monkey, mandrill, chimpanzee, barbary ape and cynomolgus and rhesus macaques; incidence generally increases with age, likely due to cumulative exposure to parasites, infectious agents and injury.(7) Non-human primates with reactive amyloidosis often have concurrent arthritis and/or enterocolitis.Â Deposition typically occurs in the large or small intestine, or less commonly in the spleen, lymph node, liver, adrenal glands or stomach.(1,7) Affected animals often display elevated levels of alkaline phosphatase, aspartate aminotransferase, lactate dehydrogenase and serum amyloid A, in combination with decreased albumin and cholesterol on serum chemistry profiles.(8) Additionally, the cynomolgus macaque, rhesus macaque, squirrel monkey, gray mouse lemur and common marmoset have all been used as models for cerebral amyloidosis.(7)
Amyloidosis is a common age related change in laboratory mice, especially in CD-1 strains.(14) Mouse amyloidosis is typically composed of AA amyloid or AapoAII (senile amyloid) deposits, but mice are also subject to several localized forms of amyloidosis involving the brain or endocrine tumors.Â In contrast to AA amyloid, AapoAII deposition is less marked in the liver and spleen, with more deposition in adrenals, intestine, heart, lungs, thyroid and gonads.Â CBA and B6 mice are most susceptible to reactive (AA) amyloidosis, while A/J mice are resistant, and A/J and SJL mice are predisposed to AapoAII amyloidosis.(11) In hamsters, as in many other species, the incidence of amyloidosis increases with age.Â Interestingly, females are three times more likely to develop amyloidosis than males, likely due to a hamster female protein, which is similar to amyloid P.Â The liver, kidneys and adrenal glands are the most frequently involved organs.(11) Amyloidosis in gerbils has been experimentally associated with filariid infection, but it also occurs spontaneously in older animals.Â Similarly, renal amyloidosis is reported in aged rabbits, especially those that have been hyperimmunized for antibody production.(11)
As noted by the contributor, primary amyloidosis with AL amyloid is often associated with immune cell dyscrasias.Â Cutaneous amyloidosis occurs in approximately 10% of dogs and cats with extramedullary plasmactyomoas.Â Cutaneous amyloidosis in dogs is also associated with dermatomyositis and monoclonal gammopathy.Â In horses, the cause of nodular AL amyloid deposition within the skin and upper respiratory tract is unknown.(6)
In addition to AA, AL and AÎ² amyloid discussed above, islet amyloid is significant in several veterinary species.Â Islet amyloid polypeptide (IAPP) produced by pancreatic islet Î²-cells in some species of mammals, birds and fishes.Â Although the exact pathogenesis is still unknown, IAPP can be deposited in pancreatic islets as amyloid in cats, non-human primates and humans, resulting in type 2 diabetes.(16) Endocrine disorders of the pancreas have been associated with amyloid deposits in the cynomolgus macaque,(10) rhesus macaque,(5) baboon, Celebes crested macaque, and Formosan rock macaque.(7)
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