. Do innervation of germinal centre and contacts between FDC and nerve fibers be keys to understand the susceptibility difference between bovines and humans to the BSE agent?

Background: In regard to BSE and vCJD, the agent tropism for lymphoid tissues is completely different even if the infectious strain responsible and the way of inoculation are identical. During vCJD, the infectious agent crosses the digestive barrier and multiplies in lymphoid organs, before progressively reaching the brain. Indeed, in vCJD, it accumulates in the ileum, tonsils, spleen and appendix of infected individuals. In contrast, in cattle, the BSE agent has a low affinity for lymphoid tissues and mainly accumulates in the nervous system. During preclinical stages, infectivity, other than that in the peripheral nervous system or central nervous system, is confined in the distal ileum of orally infected cattle. So, it appears that, at least in the case of BSE and vCJD, host properties can influence the accumulation of the infectious agent in lymphoid organs. Objectives and methods: In this study, we analysed by confocale microscopy the mucosal innervation and the interface between nerve fibres and FDC in bovine and human tonsils using a panel of antibodies. Since differences in the innervation of lymphoid organs depending on species and on age have been reported, we analysed two categories of bovines (calves less than 12 months old and bovines older than 24 months) and two categories of humans (patients less than 5 years old and patients older than 25 years). Results: In both species, ways of innervation by-passing germinal centres could be postulated: nerve fibres are widely distributed in antigen/cell traffic area: the lamina propria, the interfollicular zone and the lymphoepithelial area. We pointed out that, only in tonsils of bovines older than 24 months, nerve fibres are observed to be in contact with FDC. In contrast, in human tonsils, no nerve fibres established contacts with FDC, whatever the age. Discussion: Innervation of germinal centres can be said to be an age-dependent dynamic process in bovines. The weak innervation of the secondary lymphoid organs could thus be a rate-limiting step to neuroinvasion in humans. This species difference could influence the way of neuroinvasion and thus, the susceptibility of bovines and humans to the BSE agent

DO THE LANDMARKS USED IN THE MODIFIED SCHOBER TEST COVER THE ENTIRE LUMBAR SPINE? PROPOSAL FOR A NEW MARKING PROCEDURE

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Distribution of nerve fibres and prion protein expression in mice Peyer’s patches

Prion pathogenesis following oral exposure is thought to involve gut-associated lymphoid tissue, which includes Peyer’s patches (PP). The antigens enter into the underlying lymphoid tissue organized in PP through the medium of M cells. Infectious prion protein (PrPres) would probably take the same way of entry and like this initiate the first stage of lympho-invasion. Theoretically, intestinal lymphoid cells can come in contact with ingested PrPres and with nerve endings of the intramural system. The distribution pattern of the nerve fibres and lymphoid cells in PP and possible contact between these two elements implicated in neuroinvasion are not yet fully elucidated. In our study, classical immunoperoxydase staining and double immunofluorescence staining analysed with a confocal microscope has been carried out on C56Bl/6 mice PP. Immunoperoxidase and immunofluorescent CD11c stainings show numerous dendritic cells (DC) in the suprafollicular dome, close to the epithelium made of enterocytes and M-cells. Confocal studies show the presence of DC in the T cell zones of Peyer's patches, and also close to B cells in the follicule and to follicular dendritic cells (FDC) in the germinal centres. The PrPc expression, fundamental in the pathogenesis of prion diseases, is notably localized in germinal centres, co-localized with the FDC network and on cellular structures close to the epithelium, co-localized with DC. Nerve fibres have been immunostained in fluorescence using antibodies raised against neurofilaments High, Medium and Low and against glial fibrillary acidic protein (GFAP). Only GFAP staining revealed the presence of some nerve fibres in the suprafollicular dome, coursing the mucosal epithelium and also at the periphery of germinal centres in close connection with numerous dendritic cells. Such results permit us to postulate that these nerve fibres and PrPc positive dendritic cells, strategically positioned under the intestinal epithelium as well as in the germinal centres close to FDC network, highly expressing PrPc and thought to replicate PrPres, may be involved in the peripheral transport of the infectious prion protein