2. What is amyloid
Amyloid (G. Amylon - STARCH) means starch-like.
Amyloid is a pathologic glycoprotein deposited in the
extracellular spaces and forms fibrils on polymerization.
3. HISTOLOGICAL CHARACTERISTICS
OF AMYLOID
• Amyloid is specially stained with Congo Red. Under polarized light,
green birefringence is noticed because of alignment of fibrils. β-
pleated sheet configuration is seen in X-ray diffraction.
• The P-component which is a glycosa-amino-glycan (GAG)
facilitates polymerization of amyloid.
• The GAG makes the amyloid to stain with iodine. The amyloid is
resistant to enzymatic digestion and progressively accumulate in
tissues until the underlying disease process persists.
4. Types/Sources of amyloid
• Amyloid associated (AA): It occurs in chronic diseases and
septic conditions. Precursor is serum amyloid associated
protein (SAA).
• Amyloid light-chain (AL): It is produced in plasmacytoma and
the precursor is immunoglobulin light-chain.
5. AMYLOIDOSIS
Definition
• It is an immunological disorder in which homogeneous,
translucent amyloid substance is deposited between capillary
endothelium and adjacent cells.
Pathogenesis
• The main event occurring in amyloidosis is the deposition of
amyloid fibrils due to abnormality of protein processing.
• The sources of amyloid may be acute phase proteins,
immunoglobulins and endocrine secretes.
6. • The amyloid forms a β-pleated sheet despite their chemical
heterogeneity. This makes the fibril resistant to digestion by
macrophages and phagocytic cells and hence accumulates in
tissues.
• The amyloid, deposited around the blood vessels is more
dangerous.
• Pressure atrophy of the adjacent cells and ischaemic anoxia
results in degeneration and necrosis.
• Due to interference with gaseous exchange, supply of
nutritents and removal of waste products and stenotic vessels,
degeneration and necrosis of cells will occur amyloid
precursor protein.
8. Primary amyloidosis
• It results from antigen-antibody reaction and deposition of its
precipitates.
• The condition is not associated with any diseases e.g. repeated
exposure to antigens as in antisera and antitoxin production in
horses and B cell dyscrasia (plasmacytoma) in humans in
which immunoglobin light chain deposition occurs.
• The soluble immunoglobulin becomes insoluble with defective
degradation.
9. Secondary amyloidosis
• The condition may be associated with chronic diseases like
tuberculosis, septic conditions and neoplasia.
• This occurs in two phases.
• In the initial preamyloid phase, there is accumulation of
reticular cells and macrophages in the spleen and other
lymphoid tissue with consequent rise in plasma SAAs and
globulins.
• During the second phase, known as amyloid phase, PAS
staining cells, amyloid deposition and fall in the SAAs level
are found.
10. • Grossly, the amyloid deposition may be diffuse or focal. The
amyloid is deposited around the central artery of splenic follicles
and it forms sheet like deposits which is referred as bacon
spleen and it may protrude resembling like a grain of sago known
as sago spleen.
• The organ is waxy in consistency and the cut surface is grayish.
• Splenic corpuscles become large, gray and translucent.
• Liver is enlarged with rounded edges, doughy in consistency, pits on
pressure and ruptures easily because of its friable nature.
• In renal amyloidosis, the organ is swollen, mottled, pale and yellow
to orange in colour
11. Effects of amyloidosis
• Hypovolumic or haemorrhagic shock may occur following hepatic rupture.
• Hepatocellular atrophy occurs from pressure and nutritional deficiency.
• In renal amyloidosis, interfere with glomerular filtration.
• The enlargement and ischaemic anoxia leads to tubular epithelial
degeneration and necrosis, marked proteinuria, nephrotic syndrome, uremia
and death
• In pancreatic amyloidosis, leads to islet cell destruction and development of
Diabetes mellitus.
• Blindness may be encountered in horses in with conjuctival amyloid
deposition.
