Mechanism of Prion Protein Absorption from Digestive Tract in Calves

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Although it has been suggested that abnormal Prion proteins are absorbed from the intestinal mucosa and infect many animal species with bovine spongiform encephalopathy (BSE), the detailed mechanisms remain clarified. The aim of the present study was to investigate Horseradish peroxidase (HRP) absorption, in which HRP was used instead of abnormal Prion proteins, and its mechanism in isolated segments of the duodenum, jejunum, ileum and colon from rabbits, sheep and Holstein calves by the methods with everted sacks and the Ussing chamber. We also observed morphological features of M cells in Peyer's patches by the immunochemical method and SEM.1)In calves, the HRP absorption was greater in the duodenum, jejunum and ileum than in the colon, and also was greater at the age of 13 weeks than at 4 weeks.2)In rabbits, the HRP absorption showed a tendency to be greater in the ileum than in the colon, and was dependent on aging, the intestine, H^+ gradient and Na^+/K^+-ATPase activities.3)In calves, the HRP absorption in the jejunum and ileum was greater at the age of 6 weeks than of 15 weeks, and was significantly decreased by the reduction of the medium pH from 7.4 to 5.4. It was also significantly increased by an addition of amiloride but not by ouabain.4)In the calf jejunal epithelium, it was indicated that M cells increase the cell number and promote the differentiation as the ruminal function develops, and accelerate the ability for absorption of higher molecules.These findings strongly suggest the possibility that the absorption of abnormal Prion proteins occur at the small intestine, mainly the ileum, after weaning.