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Development and optimization of a high-throughput assay to measure neutralizing antibodies against Clostridium difficile binary toxin.

ABSTRACT: Clostridium difficile strains producing binary toxin, in addition to toxin A (TcdA) and toxin B (TcdB), have been associated with more severe disease and increased recurrence of C. difficile infection in recent outbreaks. Binary toxin comprises two subunits (CDTa and CDTb) and catalyzes the ADP-ribosylation of globular actin (G-actin), which leads to the depolymerization of filamentous actin (F-actin) filaments. A robust assay is highly desirable for detecting the cytotoxic effect of the toxin and the presence of neutralizing antibodies in animal and human sera to evaluate vaccine efficacy. We describe here the optimization, using design-of-experiment (DOE) methodology, of a high-throughput assay to measure the toxin potency and neutralizing antibodies (NAb) against binary toxin. Vero cells were chosen from a panel of cells screened for sensitivity and specificity. We have successfully optimized the CDTa-to-CDTb molar ratio, toxin concentration, cell-seeding density, and sera-toxin preincubation time in the NAb assay using DOE methodology. This assay is robust, produces linear results across serial dilutions of hyperimmune serum, and can be used to quantify neutralizing antibodies in sera from hamsters and monkeys immunized with C. difficile binary toxin-containing vaccines. The assay will be useful for C. difficile diagnosis, for epidemiology studies, and for selecting and optimizing vaccine candidates.

SUBMITTER: Xie J

PROVIDER: S-EPMC4018877 | biostudies-literature | 2014 May

REPOSITORIES: biostudies-literature

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Development and optimization of a high-throughput assay to measure neutralizing antibodies against Clostridium difficile binary toxin.

Xie Jinfu J Horton Melanie M Zorman Julie J Antonello Joseph M JM Zhang Yuhua Y Arnold Beth A BA Secore Susan S Xoconostle Rachel R Miezeiewski Matthew M Wang Su S Price Colleen E CE Thiriot David D Goerke Aaron A Gentile Marie-Pierre MP Skinner Julie M JM Heinrichs Jon H JH

Clinical and vaccine immunology : CVI 20140312 5

Clostridium difficile strains producing binary toxin, in addition to toxin A (TcdA) and toxin B (TcdB), have been associated with more severe disease and increased recurrence of C. difficile infection in recent outbreaks. Binary toxin comprises two subunits (CDTa and CDTb) and catalyzes the ADP-ribosylation of globular actin (G-actin), which leads to the depolymerization of filamentous actin (F-actin) filaments. A robust assay is highly desirable for detecting the cytotoxic effect of the toxin a ...[more]

PMID: 24623624

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Project description:Clostridioides difficile is a Gram-positive opportunistic human pathogen that causes 15,000 deaths annually in the United States, prompting a need for vaccine development. In addition to the important toxins TcdA and TcdB, binary toxin (CDT) plays a significant role in the pathogenesis of certain C. difficile ribotypes by catalyzing the ADP-ribosylation of actin in host cells. However, the mechanisms of CDT neutralization by antibodies have not been studied, limiting our understanding of key epitopes for CDT antigen design. Therefore, we isolated neutralizing monoclonal antibodies against CDT and characterized their mechanisms of neutralization structurally and biochemically. Here, 2.5-Å and 2.6-Å resolution X-ray crystal structures of the antibodies BINTOXB/22 and BINTOXB/9, respectively, in complex with CDTb-the CDT subunit that forms a heptameric pore for the delivery of toxic CDTa enzyme into the host cytosol-showed that both antibodies sterically clash with adjacent protomers in the assembled heptamer. Assessment of trypsin-induced oligomerization of the purified CDTb protoxin in vitro showed that BINTOXB/22 and BINTOXB/9 prevented the assembly of di-heptamers upon prodomain cleavage. This work suggests that the CDT oligomerization process can be effectively targeted by antibodies, which will aid in the development of C. difficile vaccines and therapeutics. IMPORTANCE Clostridioides difficile strains associated with worse clinical outcomes have been found to secrete a toxin called CDT (or binary toxin). As blocking the function of this toxin could help mitigate C. difficile infections, we sought to determine the molecular basis for the inhibition of CDT by monoclonal antibodies. We isolated monoclonal antibodies targeting the B-component of CDT (CDTb) and selected two with neutralizing activity for detailed structural and biochemical characterization. High-resolution crystal structures of each antibody bound to CDTb showed that their presence would preclude the assembly of a CDTb oligomer required for activity. Oligomerization of CDTb in vitro was shown to be blocked in the presence of the neutralizing antibodies, but not a control antibody.

Project description:Measles virus is highly infectious and remains a leading cause of vaccine preventable deaths in children. Neutralizing antibody responses elicited by measles virus infection or immunization are a serological correlate of protection. We describe a high-throughput neutralization assay to improve surveillance for measles immunity. Measles virus-antibody mixtures were incubated on Vero cell monolayers and 24 hours later cell-lysates harvested and subjected to one-step SYBR green RT-qPCR to amplify a target sequence within the measles virus nucleoprotein gene. Neutralization endpoint titers were interpolated to determine the dilution that inhibited the relative amplicon copy number by at least 90% compared to the mean signal obtained in virus control wells in the absence of serum. Anti-measles virus and anti-measles hemagglutinin antisera specifically neutralized measles virus in the microneutralization RT-qPCR assay while pre-immune sera and sera raised against other viruses did not. The microneutralization RT-qPCR assay obeyed the Percentage Law for measles virus inputs ranging from 100-5000 TCID50/well. The linear range of the assay corresponds to measles antibody concentrations of 30 to 3000 mIU/mL. Bland-Altman analysis and two-way analysis of variance demonstrated that results obtained using the microneutralization RT-qPCR assay were comparable to those obtained using a plaque reduction neutralization test and correctly identified human serum samples that were seropositive (95% and 100%, sensitivity and specificity, respectively). Furthermore, these comparisons suggest that a concentration of 300 mIU/mL may be a conservative cut-point to use to identify individuals likely to be protected against severe measles disease when the endpoint is based on 90% inhibition of virus replication. Measles virus microneutralization RT-qPCR is a rapid, sensitive, specific, and robust assay for detecting measles neutralizing antibodies that may help to improve immunization strategies nationally and achieve measles elimination globally.

Dataset Information

Development and optimization of a high-throughput assay to measure neutralizing antibodies against Clostridium difficile binary toxin.

Publications

Development and optimization of a high-throughput assay to measure neutralizing antibodies against Clostridium difficile binary toxin.

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