HLA in French patients with variant Creutzfeldt-Jakob disease

The case for involvement of spiroplasma in the pathogenesis of transmissible spongiform encephalopathies

Spiroplasma biofilm formation explains the role of these wall-less bacteria in the pathogenesis of transmissible spongiform encephalopathies (TSEs). Spiroplasma embedded in the biofilm polysaccharide matrix are markedly resistant to physical and chemical treatment, simulating the biologic properties of the TSE agent. Microcolonies of spiroplasma embedded in biofilm bound to clay are the likely mechanism of lateral transmission of scrapie in sheep and chronic wasting disease in deer via soil ingestion. Spiroplasma in biofilm bound to the stainless steel of surgical instruments may also cause iatrogenic transmission of Creutzfeldt-Jakob disease. Sessile spiroplasma in biofilm attach to the surface by curli-like fibrils, a functional amyloid that is important for spiroplasma entering cells. Curli fibers have been shown to interact with host proteins and initiate formation of a potentially toxic amyloid that multiplies by self-assembly. In TSE, this mechanism may explain how spiroplasma trigger the formation of prion amyloid. This possibility is supported by experiments that show spiroplasma produce α-synuclein in mammalian tissue cultures. The data linking spiroplasma to neurodegenerative diseases provide a rationale for developing diagnostic tests for TSE based on the presence of spiroplasma-specific proteins or nucleic acid. Research efforts should focus on this bacterium for development of therapeutic regimens for Creutzfeldt-Jakob disease.

Prion diseases: current understanding of epidemiology and pathogenesis, and therapeutic advances

The bovine spongiform encephalopathy (BSE) epidemic, along with the related threat to human health posed by the transmission of the BSE agent to humans, has highlighted the importance of prion diseases. These fatal neurodegenerative diseases are characterised by spongiform changes in the CNS, and comprise a wide spectrum of clinicopathological entities in humans and animals, such as Creutzfeldt-Jakob disease (CJD) and its emerging new variant (vCJD) in humans, and BSE and scrapie in animals. This article reviews the geographical distribution and the temporal trends of CJD and vCJD; the major events in the pathogenesis of prion diseases; the risk factors for sporadic CJD and vCJD; and the possible strategies for treating them. Worldwide statistics indicate that sporadic CJD has a stable incidence of one case per million people per year; in contrast, the incidence of vCJD appears to have increased exponentially from its characterisation in 1994 to a peak in 2000. As of December 2005, 183 definite or probable cases of vCJD had been reported worldwide. The crucial event in the pathogenesis of prion diseases is the conversion of the normally occurring cellular prion protein (PrP(c)) into a pathogenic form, called protease-resistant PrP (PrP(res)) or scrapie PrP (PrP(sc)). Pathogenetic studies in rodent models have shown that PrP(sc) is found in the enteric nervous system and in the gut-associated lymphoid tissue following oral scrapie ingestion. The role of the lymphoreticular system in the pathogenesis of TSE seems to be related to the strains of agents and the host genotype. Therapeutic approaches to vCJD are mainly based on the inhibition or prevention of the pathological change that creates PrP(sc). Derivatives of acridine (such as mepacrine [quinacrine]) and the phenothiazine psychotropics have been proposed as possible therapies because of their activity in cellular models; however, neither class was able to affect the protease resistance of preexisting PrP fibrils. More encouragingly, in animal models of prion disease, tetracyclines were found to reduce prion infectivity by direct inactivation of PrP(sc). While these findings are promising, the suitability of these compounds for clinical use is still limited by their low efficacy once symptoms are apparent. Treatments based on the vaccination approach have also produced positive results, but further investigations are necessary to establish their clinical application.

Genetic risk factors associated with Creutzfeld-Jakob disease in Slovenians and a rapid typing for PRNP codon 129 single nucleotide polymorphism

PRNP has been the most informative marker for the predisposition to variant Creutzfeld-Jakob disease (vCJD). All victims of the vCJD carried methionine (M) at the position 129 of the PrP. Prions could travel through the immune system to get from the gut to the brain, and human leucocyte antigens (HLAs) could be involved in this carriage, with HLA-DQ7 being less efficient. Contradictory reports have raised the question of the influence of sampling in population studies. We developed a fast and reliable real-time polymerase chain reaction for codon 129 single nucleotide polymorphism (SNP) using TaqMan technology, which overcomes the main drawbacks of other methods and analysed Slovenian population (n = 97). The comparison with other populations served for the estimation of the genetic risk for the development of vCJD in Slovenians. The frequencies at the codon 129 SNP in the Slovenian population were 43.3% M, 45.4% M/V 11.3% V. Considerable differences between the DQ7 frequencies in diverse samples from the same population can be seen, especially when compared to Slovenian population. This could be because of the diverse criteria for including subjects into the study and the sampling of geographically distinct subpopulations. Analysing the adequacy of HLA-DQ7 as a possible predictive factor for developing Creutzfeld-Jakob disease (CJD) by case - control studies could be improved with exact and equal sampling of groups of patients and controls. CJD genetic risk factors in the Slovenians were not found significantly different than those in British.

MHC class II signaling in antigen-presenting cells

The MHC class II molecules have been recognized as signaling receptors for more than a decade, and recent work has revealed the importance of their signaling for the immune response. Today, we know that the function of MHC class II molecules on antigen-presenting cells (APCs) is not limited to their role as antigen-presenting structures; they are flexible receptors that, by triggering a variety of signaling pathways, can regulate APC activities from proliferation and maturation to apoptosis. Recent advances have provided insights into how these molecules might accommodate such regulation.

The Epidemiology of Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) was identified as a new disease in 1996. It was linked to infection with the bovine spongiform encephalopathy (BSE) agent although the epidemiological evidence for this was not strong, but later strain typing studies confirmed the association. The disease has affected predominantly young adults whose dietary and other characteristics are unexceptional compared to control groups, other than that all patients to date have been methoinine homozygous at codon 129 of the prion protein gene and the incidence has been about two times higher in the North of the UK. The number of cases in the 7 years after first identification of the disease has been considerably lower than initially feared, given the likely widespread exposure of the UK population to the BSE agent through contaminated beef products. Predictions of the possible future course of the epidemic have many associated uncertainties, but current mathematical models suggest that more than a few thousand cases is unlikely. Such modelling is limited by the absence of a test for infection with the vCJD agent. The development of a test that could be used on easily accessible tissue to detect infection early in the incubation period would not only advance understanding of the epidemiology of infection with the agent but would also aid the implementation of control measures to prevent potential iatrogenic spread.