Altered lymphocyte homeostasis after oral prion infection in mouse.

Transmissible spongiform encephalopathies (TSEs) or prion diseases develop as central nervous system (CNS) disorders characterized by extremely long incubation periods. Although TSEs do not go along with inflammatory infiltrates and/or antibody production against the prion protein (PrP(Sc)), the immune system plays an important role in pathogenesis as long as different lymphoid organs (Peyer's patches, lymph nodes and spleen) may facilitate the accumulation and further spread of prions after peripheral exposure. In this work we investigated the changes in lymphoid and dendritic cell (DC) populations as well as the implications of different cytokines during disease progression after experimental oral inoculation of prions in a transgenic mouse model. At different days post-inoculation (dpi), T and B lymphocytes and DC populations from lymphoid organs, blood and brain were analyzed by flow cytometry and immunohistochemistry. Besides time related variations in lymphoid cell numbers due to the aging of the animals significant changes related with the infection were found in mesenteric lymph nodes, peripheral blood leukocytes (PBLs) as well as in spleen, affecting the CD4/CD8 ratio. In contrast, little or no variation was detected in Peyer's Patches or in thymus either associated with aging or the infection status. At individual time points significant differences between infected and control mice were seen in the CD8, CD4 and DC populations, with less evidence of differences in the B cell compartment. Finally, a pro-inflammatory phenotype occurred at early times in the spleen, where the levels of lymphotoxin-beta mRNA were found augmented with respect to controls. Altogether, these results suggest that normal regulation of lymphocyte populations becomes altered along the progression of a prion infection.

Transgenic mice expressing bovine PrP with a four extra repeat octapeptide insert mutation show a spontaneous, non-transmissible, neurodegenerative disease and an expedited course of BSE infection.

Transgenic (Tg) mice carrying four extra octapeptide repeats (OR) in the bovine PrP gene (10OR instead of 6) have been generated. In these mice, neuropathological changes were observed depending upon the level of transgene expression. These changes primarily involved a slowly advancing neurological disorder, characterized clinically by ataxia, and neuropathologically, by vacuolization in different brain areas, gliosis, and loss of cerebellar granule cells. Accumulation of insoluble bovine 10OR-PrP (bo10OR-PrP) was observed depending on the level of expression but no infectivity was found associated with this insoluble form. We also compared the behavior of bo6OR-PrP and bo10OR-PrP Tg mouse lines in response to BSE infection. BSE-inoculated bo10ORTg mice showed an altered course of BSE infection, reflected by reduced incubation times when compared to bo6ORTg mice expressing similar levels of the wild type 6OR-PrP. In BSE-inoculated mice, it was possible to detect PrP(res) in 100% of the animals. While insoluble bo10OR-PrP from non-inoculated bo10ORTg mice was non-infectious, brain homogenates from BSE-inoculated bo10ORTg mice were highly infectious in all the Tg mouse lines tested. This Tg mouse model constitutes a new way of understanding the pathobiology of bovine transmissible spongiform encephalopathy. Its potential applications include the assessment of new therapies against prion diseases.