We established that follicular dendritic cells (FDCs) are the site of abnormal prion protein (PrPCJD) accumulations in lymphoid tissues from mice infected with Creutzfeldt-Jakob disease. Evidence of positive FDC staining was observed in Creutzfeldt-Jakob disease-infected mice irrespective of the inoculation route, while no such staining was seen in the control mice. We also found that the severe combined immunodeficiency mouse trait is transmittable via the intracranial route but not via the intraperitoneal route. Mice with severe combined immunodeficiency did not have PrPCJD accumulation in FDCs.

A redacted prion protein (PrP) of 106 amino acids with two large deletions was expressed in transgenic (Tg) mice deficient for wild-type (wt) PrP (Prnp0/0) and supported prion propagation. RML prions containing full-length PrP(Sc)produced disease in Tg(PrP106)Prnp0/0 mice after approximately 300 days, while transmission of RML106 prions containing PrP(Sc)106 created disease in Tg(PrP106) Prnp0/0 mice after only approximately 66 days on repeated passage. This artificial transmission barrier for the passage of RML prions was diminished by the coexpression of wt MoPrPc in Tg(PrP106)Prnp+/0 mice that developed scrapie in approximately 165 days, suggesting that wt MoPrP acts in trans to accelerate replication of RML106 prions. Purified PrP(Sc)106 was protease resistant, formed filaments, and was insoluble in nondenaturing detergents. The unique features of RML106 prions offer insights into the mechanism of prion replication, and the small size of PrP(Sc)106 should facilitate structural analysis.

The N terminus of the scrapie isoform of prion protein (PrP Sc ) can be truncated without loss of scrapie infectivity and, correspondingly, the truncation of the N terminus of the cellular isoform, PrP C , still permits conversion into PrP Sc . To assess whether additional segments of the PrP molecule can be deleted, we previously removed regions of putative secondary structure in PrP C ; in the present study we found that deletion of each of the four predicted helices

The prion diseases are an unusual group of fatal neurodegenerative disorders which include Creutzfeldt-Jakob disease, fatal familial insomnia, and Gerstmann-Sträussler-Scheinker disease in humans as well as bovine spongiform encephalopathy in cattle and scrapie in sheep and goats. A wealth of evidence supports the hypothesis that these diseases are caused by a conformational change in the prion protein (PrP) from its normal, cellular isoform (PrP C ) into a pathogenic, infectious isoform (PrP Sc ) (17,18,21). To investigate the pathogenesis of prion diseases and to identify potential therapeutic targets, much effort is now directed toward characterizing the structural biology of PrP Sc formation. Recent nuclear magnetic resonance studies of recombinant PrP molecules provide evidence for a three-␣-helix bundle protein with a short ␤-strand region and a relatively unstructured N terminus (4,7,9,23,24). These structural data have facilitated the rational analysis of mutagenesis-specific PrP segments in order to determine their importance for prion propagation.As part of a systematic PrP deletion mutagenesis study, we discovered that Tg(MHM2,⌬23-88)9381/Prnp 0/0 mice expressing N-terminally truncated MHM2 PrP molecules were resistant to Rocky Mountain Laboratory (RML) murine prions (30). MHM2 is a chimeric construct that differs from wild-type mouse (Mo) PrP at positions 108 and 111 (28). Substitution at these positions with the homologous residues from the Syrian hamster (SHa) PrP sequence (L108M and V111M) creates an epitope for the anti-PrP 3F4 monoclonal antibody (MAb) (8). Although Tg(MHM2,⌬23-88)9381/Prnp 0/0 mice failed to propagate RML prions, MHM2(⌬23-88) molecules expressed in scrapie-infected mouse neuroblastoma (ScN2a) cells successfully formed protease-resistant MHM2(⌬23-88)PrP Sc (13). Furthermore, Tg(MHM2,⌬23-88)9381/Prnp ϩ/0 mice expressing endogenous MoPrP in addition to the truncated, chimeric transgene were susceptible to RML prion infection. These heterozygote mice developed scrapie ϳ260 days after inoculation with RML prions, and biochemical analysis revealed the accumulation of protease-resistant MHM2(⌬23-88)PrP Sc in their brains (30). These complementary results in ScN2a cells and Prnp ϩ/0 mice indicate that coexpression of MoPrP facilitates the conversion of MHM2(⌬23-88)PrP C to MHM2(⌬23-88)PrP Sc . In view of the foregoing results, it remained unclear why Tg(MHM2,⌬23-88)9381/Prnp 0/0 mice were not susceptible to RML prions in the absence of MoPrP. Immunofluorescence studies did not reveal any significant differences in the cellular localization of truncated, chimeric, and wild-type PrP molecules in transfected mouse neuroblastoma (N2a) cells (data not shown). Possible explanations for the resistance of Tg-(MHM2,⌬23-88)9381/Prnp 0/0 mice to prion infection include (i) a prion transmission barrier between full-length mouse PrP and MHM2(⌬23-88), (ii) decreased prion conversion efficiency caused by removal of the N terminus, (iii) insufficient expression of the MHM2(⌬23-88) transgene, and (iv) ...