Critical factors influencing prion inactivation by sodium hydroxide.

BACKGROUND AND OBJECTIVES: Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseases caused by aberrantly folded cellular proteins (PrP(Sc); prions) that are generally resistant to conventional pathogen-inactivation techniques. To ensure effective decontamination and inactivation of prions that could be present in source material, we investigated critical factors that influence prion inactivation by NaOH. MATERIALS AND METHODS: A decrease in prion infectivity correlates with the disappearance of the protease-resistant core of PrPSc (PrPRES) observed in biochemical assays. To model prion inactivation, hamster scrapie (strain 263K) brain homogenate (SBH) was incubated for specific periods of time in 0.1 m NaOH at 4 or 18 degrees C, with or without detergent. Neutralized samples were subjected to limited digestion with proteinase K (PK) and then analysed using an endpoint dilution western blot assay and antibody 3F4. Structural changes in prions exposed to NaOH were examined using differential immunoprecipitation. RESULTS: Treatment of SBH with 0.1 m NaOH for 15 min, in the absence of detergent, at 4 and 18 degrees C caused a reduction in the PrP(RES) signal of 3.5 and 4.0 log10 units, respectively, with some residual signal remaining. The presence of the detergent sarkosyl during a 60-min incubation in NaOH further enhanced PrPRES reduction to > or = 4.5 log10 units (i.e. below the limit of detection). NaOH treatment induced conformational changes in PrP that resulted in the exposure of a hidden epitope and enabled prion immunoprecipitation by antibody 3F4. CONCLUSIONS: The use of NaOH can effectively reduce prion levels in an in vitro inactivation assay. After pretreatment of SBH with detergent, NaOH completely eliminates the PrPRES signal. Detergent may liberate lipid membrane-protected PrPSc to improve access to NaOH, which can then inactivate PrPSc by altering its structure. In cases of unidentified exposure to PrPSc during manufacturing, sanitizing procedures combining the use of detergent and NaOH may help to ensure minimal levels of contamination carryover in products.

Inactivation of West Nile virus, vaccinia virus and viral surrogates for relevant and emergent viral pathogens in plasma-derived products.

BACKGROUND AND OBJECTIVES: Human plasma is the source of a wide variety of therapeutic proteins, yet it is also a potential source of viral contamination. Recent outbreaks of emergent viral pathogens, such as West Nile virus, and the use of live vaccinia virus as a vaccine have prompted a reassessment of the viral safety of plasma-derived products. The purpose of this study was to evaluate the efficacy of current viral inactivation methods for West Nile and vaccinia viruses and to reassess the use of model viruses to predict inactivation of similar viral pathogens. MATERIALS AND METHODS: Virus-spiked product intermediates were processed using a downscaled representation of various manufacturing procedures. Virus infectivity was measured before and after processing to determine virus inactivation. RESULTS: The results demonstrated effective inactivation of West Nile virus, vaccinia virus and a model virus, bovine viral diarrhoea virus, during pasteurization, solvent/detergent treatment and caprylate treatment. Caprylate provided rapid and effective inactivation of West Nile virus, vaccinia virus, duck hepatitis B virus and Sindbis virus. Inactivation of West Nile virus was similar to that of bovine viral diarrhoea virus. CONCLUSIONS: This study demonstrates that procedures used to inactivate enveloped viruses in manufacturing processes can achieve inactivation of West Nile virus and vaccinia virus. In addition, the data support the use of model viruses to predict the inactivation of similar emergent viral pathogens.

Persistent infection of rabbits with bovine immunodeficiency-like virus.

Chronic infection of rabbits was induced by a single intraperitoneal injection of bovine immunodeficiency-like virus (BIV)-infected cells. Ten BIV-infected animals were monitored serologically for up to 2 years. Results of serologic and virus rescue assays indicated that all animals became infected and demonstrated a rapid and sustained BIV-specific humoral response. BIV was rescued by cocultivation from spleen, lymph nodes, and peripheral blood leukocytes of infected animals. Viral DNA in immune tissues was confirmed by polymerase chain reaction amplification of BIV sequences. These data and specific immunohistochemical staining of mononuclear cells of the spleen for BIV antigen suggest that the infection is targeted to immune system cells.

Role of hepatocytes and Kupffer cells in age-dependent murine hepatitis caused by a phlebovirus, Punta Toro.

Punta Toro virus (PTV) infection of C57BL/6 mice results in fulminant hepatic necrosis and death in 3-week-old susceptible mice, but survival with minimal hepatocellular necrosis in 8-week-old resistant mice. Susceptibility in 3-week-old mice is associated with an earlier rise of viral titers in liver and serum than that occurring in 8-week-old resistant mice. There is also an earlier and more rapid accumulation of infectious progeny in serum vs. liver after PTV infection in both age groups, suggesting that the virus may replicate in extrahepatic sites as well as the liver. PTV infection of isolated hepatocytes and Kupffer cells from 3- and 8-week-old mice demonstrates a significant age-related difference in the ability of these cells to support replication of PTV in vitro (P less than 0.05). The age-related difference in liver cell-PTV interaction appears to be an inherent difference in the liver cells themselves, since there are no age-related differences in viral adsorption, morphogenesis, cytopathic effect, or interferon action within these cells. Thus, age-related differences in PTV replication or dissemination at extrahepatic sites, and the ability of the virus to replicate in intrahepatic sites, may be additive factors in the expression of age-related susceptibility to PTV in C57BL/6 mice.

Development of the bovine immunodeficiency-like virus as a model of lentivirus disease.

The bovine immunodeficiency-like virus (BIV) is morphologically, serologically, and genetically related to the lentivirus subfamily of retroviruses which includes human and simian immunodeficiency viruses and other lentiviruses causally associated with debilitating diseases of domestic animals. There are many parallels in the biology and pathologic characteristics of BIV infections with those of HIV that make its development as a model of HIV-like infection and disease potentially attractive. In order to obtain a better understanding of the molecular basis of BIV-induced disease, two biologically active proviruses of BIV were molecularly cloned and sequenced. The BIV genome is 9.0 kilobases in the form of the proviral DNA. It contains the obligate retroviral structural genes, gag, pol, and env. In addition, in the BIV central region, between and overlapping pol and env, there are five potential coding regions for non-structural/regulatory genes; three are analogous to vif, tat, and rev in HIV and two, called W and Y, are unique to BIV. There is no coding region analogous to nef in BIV. Sequence comparisons of two functional proviruses obtained from the DNA of cells carrying an infection from a single virus isolation indicate that the genome of BIV is highly variable within a single biological isolate. Moreover, the greatest number of substitutions occur in the env gene. The results suggest the presence of multiple genotypes which may be of significance in defining the disease potential of a BIV isolate. These clones will be useful in dissecting the replicative cycle and mechanisms of pathogenesis of BIV in various animal models.

Junin virus monoclonal antibodies: characterization and cross-reactivity with other arenaviruses.

Twenty-one monoclonal antibodies reactive with Junin virus structural proteins were produced and characterized. Using radioimmunoprecipitation and Western blot assays, 13 were found to react with the nucleoprotein, seven with the surface glycoprotein and one failed to react, but showed a fluorescent antibody staining pattern consistent with other glycoprotein-specific antibodies. In radioimmunoprecipitation assays, glycoprotein-specific monoclonal antibodies reacted not only with the 35K structural glycoprotein, but also with what is presumed to be the glycoprotein precursor. Four of seven glycoprotein-specific antibodies neutralized Junin virus to high titres. Cross-reactivity with other arenaviruses was found to be restricted to nucleoprotein-specific monoclonal antibodies and occurred only with New World arenaviruses. Cross-reactivity also shows the Junin virus to be most closely related to Machupo and Tacaribe viruses.

Effects of ribamidine, a 3-carboxamidine derivative of ribavirin, on experimentally induced Phlebovirus infections.

Ribamidine (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamidine) was inhibitory in rhesus monkey kidney (LLC-MK2 derivative) cells to Adames and Balliet strains of Punta Toro virus (PTV), a Phlebovirus related to Rift Valley fever and sandfly fever viruses. The 50% effective dose was 8 and 12 micrograms/ml against each respective virus strain; the 50% cytotoxic dose was 320 micrograms/ml, giving selectivity indices of 40 and 27 against each virus strain. The virus ratings were 1.2 and 1.0, respectively. In radiolabel uptake studies, ribamidine had a moderate effect on [3H]leucine uptake at dosages down to 1 microgram/ml, but [3H]thymidine, [32P], and [3H]uridine were inhibited at high (100-1000 micrograms/ml) doses only. Subcutaneous (s.c.) and oral treatments of Adames PTV-infected mice were equally highly effective, as evidenced particularly by 100% survivors. Reduced hepatic icterus, serum oxalic acid transaminase, serum glutamic pyruvic acid transaminase, and recoverable virus titers from livers and sera of infected mice were also seen as a result of ribamidine treatment. Twice daily treatment for 5 days could be started as late as 72 h post-virus inoculation (p.v.i.) with significant inhibition of PTV infection seen. Single s.c. treatments administered as late as 48 h p.v.i. were similarly effective. Using the chronic therapy schedule, the maximum tolerated dose was 1000 mg/kg/day and the minimum effective dose was 31.3 to 62.5 mg/kg/day. Using single treatment, a maximum tolerated dose was greater than 1000 mg/kg, and the minimum effective dose was 125 mg/kg. Ribamidine s.c. treatment of mice infected intracerebrally with the Balliet strain of PTV resulted in a moderate infection-inhibitory effect, seen especially by reduced virus titers in the brains of the infected, treated mice.

Antigenic analysis of Punta Toro virus and identification of protective determinants with monoclonal antibodies.

Hybridomas producing monoclonal antibodies to the three major structural proteins of Punta Toro virus (PTV) were established by fusion of spleen cells with Sp2/0-Ag-14 mouse plasmacytoma cells. Thirty-six independently derived monoclonal antibodies were evaluated in neutralization, hemagglutination inhibition, and ELISA assays and the isotype, antigen specificities, and cross-reactivities were determined. These antibodies were also assessed for their ability to provide protection in a murine model. Both G1- and G2-specific antibodies were obtained which neutralized virus infectivity in vitro and inhibited hemagglutination, whereas nucleocapsid-specific antibodies exhibited neither activity. All of the anti-G1 antibodies were PTV-specific, whereas anti-G2 and anti-nucleocapsid antibodies exhibited varying patterns of cross-reactivity with heterologous phleboviruses. All of the G1-reactive monoclonal antibodies, which bound to epitopes in two distinct topological sites as determined by competitive binding assays, provided efficient protection to both immunocompetent and immunosuppressed mice. In contrast, of the 23 G2-reactive antibodies, only 8 were able to protect immunocompetent mice and only one was able to protect immunosuppressed animals. The degree of protection achieved in vivo did not correlate directly with the neutralization titers determined in vitro.

In vitro and in vivo Phlebovirus inhibition by ribavirin.

Ribavirin (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) was markedly inhibitory in vitro to Adames and Balliet strains of Punta Toro virus (PTV), a Phlebovirus related to Rift Valley fever and sandfly fever viruses. By using inhibition of viral cytopathic effect in LLC-MK2 cells with both virus strains, the 50% effective dose was 4 to 10 micrograms/ml and the virus rating was 1.3. The Adames strain of PTV infection in mice was established for evaluation of the in vivo antiviral efficacy of ribavirin. The drug was administered subcutaneously (s.c.) twice daily for 5 to 7 days beginning 4 h pre-virus inoculation, 24 h post-virus inoculation, or 36 h post-virus inoculation, with increased survivors, reduced hepatic icterus, reduction of serum glutamic oxalic acid transaminase and serum glutamic pyruvic acid transaminase, and inhibition of infectious virus from sera and livers of infected mice. The minimum effective dose was 4.7 mg/kg per day, with a maximum tolerated dose of 75 mg/kg per day. When the same treatment schedule beginning 4 h pre-virus inoculation, 4 h post-virus inoculation, or 24 h post-virus inoculation was used, orally administered ribavirin was effective at doses as low as 6.3 mg/kg per day. Single s.c. ribavirin treatments at doses of 175 to 700 mg/kg administered from 4 to 48 h post-virus inoculation were also effective. No effect was seen when ribavirin was administered s.c. to mice infected intracerebrally with the PTV strain Balliet, even though treatment was begun 36 h before virus exposure.

Punta Toro virus infection of C57BL/6J mice: a model for phlebovirus-induced disease.

Punta Toro virus infections of inbred strains of mice have been characterized and evaluated as a model in which to study various aspects of the host response to phlebovirus infections and the requirements for protective immunity. The Adames strain of Punta Toro virus was found to be strongly hepatotropic and lymphotropic and the outcome of infection was largely a function of age. C57BL/6J mice of less than 5 weeks of age uniformly developed fulminant hepatocellular necrosis with mean survival times of 4.2 days. Resistance to lethal infection increased with age such that greater than 95% of 8-week-old mice survived challenge. The kinetics of viremia, antibody production, and hematological changes in 4- and 8-week animals indicated that the survival of the older animals is related to their ability to delay virus replication and the development of hepatic lesions during the initial 48 h of infection and their ability to terminate virus replication and clear virus from the circulation 4 to 5 days after infection. The mechanisms responsible for this resistance were studied using anti-interferon serum, immunosuppression, and passive immunization.