AA amyloidosis induced in sheep principally affects the gastrointestinal tract

AA amyloidosis was initiated experimentally in adult sheep by induction of gangrenous pneumonia, an inflammatory process known to be associated with amyloid formation. A vegetable fragment contaminated with rumen content was instilled into the lungs of 4 experimental animals. A fifth animal was not inoculated and served as control. The animals were examined daily and blood and urine were sampled biweekly post-inoculation. One sheep was killed 18 days post-inoculation (dpi), another 49dpi, and the remaining two (as well as the control animal) 63dpi. Respiratory signs, diarrhoea and/or soft, unformed stool were observed in all inoculated sheep. All experimental animals developed gangrenous pneumonia with hypoalbuminaemia and hypergammaglobulinaemia, and elevated urinary protein, creatinine, gamma glutamyl transferase and ss-glucuronidase. Amyloid deposition was most pronounced in the gastrointestinal tract and was evident from 18dpi. Amyloid was present from the tongue to the rectum, but was most prominent in the duodenum where the deposits disrupted the normal mucosal architecture. Other body organs had only mild amyloid deposition. Immunohistochemistry confirmed that the deposits were AA amyloid. These findings suggest that the gastrointestinal tract is the main target organ for AA amyloid deposition in sheep. The observations in this experimental model must now be confirmed in animals with spontaneously arising AA amyloidosis.