Transmissible ileal hyperplasia of hamsters. I. Histogenesis and immunocytochemistry.

Transmissible ileal hyperplasia (TIH) was experimentally induced in weanling hamsters, and the development of lesions was characterized. Ileal lesions developed in two phases: a hyperplastic phase which was detected by Day 10 and an inflammatory phase which began by Day 20. Hyperplasia began as focal lengthening of villi with expansion of crypt-type epithelium onto villus walls. Diffuse hyperplasia of distal ileum developed; dilated, tortuous crypts penetrated subjacent supporting tissues; but metastases were not seen. Inflammation began in association with focal or segmental necrosis of crypt epithelium, and crypt abscesses developed. Severe pyogranulomatous inflammation of the ileal wall, focal peritonitis, mesenteric lymphadenitis, and portal hepatitis were common in advanced lesions. Development of ileal lesions was closely correlated with accumulation of particulate antigen, detectable by immunofluorescence, in the cytoplasm of mucosal epithelial cells. Antigen was also detected in ileal granulomas, mesenteric lymph nodes, and liver. There was simultaneous development of serum antibody specific for intracytoplasmic antigen. These studies comfirm that mucosal hyperplasia is the primary lesion in TIH.