Characterization of bovine and human cellular prion protein expressed in the central nervous system and in lymphoid organs.

Prion cell tropism varies significantly among animal species, depending on both the agent strain and host-specific factors. For example, prions show high lymphotropism in scrapie infected sheep and vCJD, but little, if any, in sCJD or BSE. In particular, the BSE strain is associate with significant PrP-res accumulation in tonsils, spleen and appendix in humans, whereas, it is largely confined to the nervous system in 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. Given that the normal cellular prion protein (PrPC), is sine qua non for PrP-res formation and the development of TSE, it appears reasonable to hypothesize that tissue-specific PrPC properties may represent one of the host factors influencing the cell tropism of the infectious agent in human or bovine. We applied a western blot analyses to compare the relative percentage of the di-, mono- and unglycosylated PrPC (the so called glycoform ratio) as well as the expression of truncated PrPC forms in tissues from the central nervous system and lymphoid structures (lymphoid follicles, lymphocytes and follicular dendritic cells) of both bovine and human. We found that PrPC glycoform ratio is significantly different between cerebellum and medulla in both bovine and human. Moreover, the expression of truncated forms of PrPC (i.e. 21 and 18 kDa PrPC) was also significantly heterogenous according to the brain region investigated. PrPC was highly glycosylated in spleen and lymphoid follicles isolated from bovine tonsils, mesenteric lymph nodes, ileal and jejunal Peyer’s patches. After deglycosylation, a novel PrPC truncated form with a relative molecular mass of about 25 kDa was detected in bovine lymphoid organs beside the typical 18 and 21 kDa forms. No difference in WB PrPC profile was seen in human lymphocytes extracted either from spleen or tonsil. Our results highlight variation in the profile expression of PrPC in peripheral and central tissues of bovine and human. Such differences may have an implication for PrPC function or may represent critical factors influencing the accumulation of the infectious agent in these areas. Supported by the EU contract QLG3-CT-2002-81030