Permissive Models Research Articles

Cellular Aspects of Prion Replication In Vitro

Prion diseases or transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative disorders in mammals that are caused by unconventional agents predominantly composed of aggregated misfolded prion protein (PrP). Prions self-propagate by recruitment of host-encoded PrP into highly ordered β-sheet rich aggregates. Prion strains differ in their clinical, pathological and biochemical characteristics and are likely to be the consequence of distinct abnormal prion protein conformers that stably replicate their alternate states in the host cell. Understanding prion cell biology is fundamental for identifying potential drug targets for disease intervention. The development of permissive cell culture models has greatly enhanced our knowledge on entry, propagation and dissemination of TSE agents. However, despite extensive research, the precise mechanism of prion infection and potential strain effects remain enigmatic. This review summarizes our current knowledge of the cell biology and propagation of prions derived from cell culture experiments. We discuss recent findings on the trafficking of cellular and pathologic PrP, the potential sites of abnormal prion protein synthesis and potential co-factors involved in prion entry and propagation.

α-Siphons of a Suboptimal Control Model of a Subclass of Petri Nets

It has been a hot research topic to synthesize maximally permissive controllers with fewest monitors. So far, all maximally permissive control models for a well-known benchmark are generalized Petri net, which com-plicates the system. In addition, they all relied on time-consuming reachability analysis. Uzam and Zhou ap-ply First-met-bad-marking (FBM) method to the benchmark to achieve a near maximal permissive control policy with the advantage of no weighted control (WC) arcs. To improve the state of the art, it is interesting to synthesize optimal controller with as few weighted arcs as possible since it is unclear how to optimize the control for siphon involving WC arcs, This paper explores the condition to achieve optimal controller with-out WC and defining a new type of siphon, called α-siphon. If the condition is not met, one can apply the technique by Piroddi et al. to synthesize optimal controllers with WC.

Potency testing for the experimental Na-GST-1 hookworm vaccine

Over the next decade, a new generation of vaccines will target the neglected tropical diseases (NTDs). The goal of most NTD vaccines will be to reduce the morbidity and decrease the chronic debilitating nature of these often-forgotten infections – outcomes that are hard to measure in the traditional potency testing paradigm. The absence of measurable correlates of protection, a lack of permissive animal models for lethal infection, and a lack of clinical indications that do not include the induction of sterilizing immunity required us to reconsider the traditional bioassay methods for determining vaccine potency. Owing to these limitations, potency assay design for NTD vaccines will increasingly rely on a paradigm where potency testing is one among many tools to ensure that a manufacturing process yields a product of consistent quality. Herein, we discuss the evolution of our thinking regarding the design of a potency assay along these newly defined lines and its application to the release of the experimental Necator americanus-glutathione-S- transferase-1 (Na-GST-1) vaccine to prevent human hookworm infection. We discuss the necessary steps to accomplish the design and implementation of such a new potency assay as a resource for the burgeoning NTD vaccine community. Our experience is that much of the existing information is proprietary and needs to be pulled together in a single source to aid in our overall understanding of potency testing.

Human parvovirus B19 causes cell cycle arrest of human erythroid progenitors via deregulation of the E2F family of transcription factors

Human parvovirus B19 (B19V) is the only human pathogenic parvovirus. It causes a wide spectrum of human diseases, including fifth disease (erythema infectiosum) in children and pure red cell aplasia in immunocompromised patients. B19V is highly erythrotropic and preferentially replicates in erythroid progenitor cells (EPCs). Current understanding of how B19V interacts with cellular factors to regulate disease progression is limited, due to a lack of permissive cell lines and animal models. Here, we employed a recently developed primary human CD36(+) EPC culture system that is highly permissive for B19V infection to identify cellular factors that lead to cell cycle arrest after B19V infection. We found that B19V exploited the E2F family of transcription factors by downregulating activating E2Fs (E2F1 to E2F3a) and upregulating repressive E2Fs (E2F4 to E2F8) in the primary CD36(+) EPCs. B19V nonstructural protein 1 (NS1) was a key viral factor responsible for altering E2F1-E2F5 expression, but not E2F6-E2F8 expression. Interaction between NS1 and E2F4 or E2F5 enhanced the nuclear import of these repressive E2Fs and induced stable G₂ arrest. NS1-induced G₂ arrest was independent of p53 activation and increased viral replication. Downstream E2F4/E2F5 targets, which are potentially involved in the progression from G₂ into M phase and erythroid differentiation, were identified by microarray analysis. These findings provide new insight into the molecular pathogenesis of B19V in highly permissive erythroid progenitors.

The immunology of human hookworm infections

Hookworms are one of the most prevalent parasites of humans in developing countries, but we know relatively little about the immune response generated to hookworm infection. This can be attributed to a lack of permissive animal models and a relatively small research community compared with those of the more high-profile parasitic diseases. However, recently, research has emerged on the development of vaccines to control hookworm infection and the use of hookworm to treat autoimmune and allergic disorders, contributing to a greater understanding of the strategies used by hookworms to modulate the host's immune response. A substantial body of research on the immunobiology of hookworms originates from Australia, so this review will summarize the current status of the field with a particular emphasis on research carried out 'down under'.

Human adenovirus replication in immunocompetent Syrian hamsters can be attenuated with chlorpromazine or cidofovir

Adenoviruses can cause severe toxicity in children and in immunocompromised adults, and therefore a means to abrogate replication would be useful. With regard to cancer treatment, replication competent oncolytic adenoviruses have been safe in humans, although their efficacy has been variable. Therefore, more effective agents are now entering clinical testing and, consequently, replication-associated side effects remain a concern. Preclinical analysis of replication related toxicity has been hampered by a lack of permissive models. Therefore, it has been difficult to study modulation of human adenovirus replication in immune competent animals. We investigated four different hamster carcinoma cell lines for transduction and cell killing potency in vitro and in vivo. Gene transfer was assessed using replication-deficient adenoviruses expressing luciferase. Cell killing was studied in vitro and in vivo using an oncolytic adenovirus that kills tumor cells by viral replication. After the most promising animal model had been selected, abrogation of virus replication was assessed in vitro and in vivo using a TCID(50) assay. The results obtained suggest wild-type adenovirus replication in all four tested Syrian hamster cell lines and also normal organs. Virus replication could be abrogated with chlorpromazine, cidofovir and cytosine arabinoside, and the effect occurred subsequent to nuclear delivery of the viral genome. Attenuation of virus replication also was seen in vivo both in tumors and the liver. Syrian hamsters may comprise a valuable immune competent model for evaluating anti-adenoviral drugs. Furthermore, chlorpromazine or cidofovir might be useful in case of adenovirus replication-associated symptoms in humans.

Lineage Commitment: Cytokines Instruct, At Last!

Instructive and permissive models of commitment have been proposed for hematopoietic cytokines. In recent issues of Science and Cell, Rieger et al. (2009) and Sarrazin et al. (2009) together show that cytokines can instruct lineage choice.

Infection outcome and cytokine gene expression in Brugia pahangi- infected gerbils (Meriones unguiculatus) sensitized with Brucella abortus.

Filarial infections have been associated with the development of a strongly polarized Th2 host immune response and a severe impairment of mitogen-driven proliferation and type 1 cytokine production in mice and humans. The role of this polarization in the development of the broad spectra of clinical manifestations of lymphatic filariasis is still unknown. Recently, data gathered from humans as well as from immunocompromised mouse models suggest that filariasis elicits a complex host immune response involving both Th1 and Th2 components. However, responses of a similar nature have not been reported in immunologically intact permissive models of Brugia infection. Brucella abortus-killed S19 was inoculated into the Brugia-permissive gerbil host to induce gamma interferon (IFN-gamma) production. Gerbils were then infected with B. pahangi, and the effect of the polarized Th1 responses on worm establishment and host cellular response was measured. Animals infected with both B. abortus and B. pahangi showed increased IFN-gamma and interleukin-10 (IL-10) and decreased IL-4 and IL-5 mRNA levels compared with those in animals infected with B. pahangi alone. These data suggest that the prior sensitization with B. abortus may induce a down regulation of the Th2 response associated with Brugia infection. This reduced Th2 response was associated with a reduced eosinophilia and an increased neutrophilia in the peritoneal exudate cells. The changes in cytokine and cellular environment did not inhibit the establishment of B. pahangi intraperitoneally. The data presented here suggest a complex relationship between the host immune response and parasite establishment and survival that cannot be simply ascribed to the Th1/Th2 paradigm.