Process development and characterization of recombinant nucleocapsid protein for its application on COVID-19 diagnosis

COVID-19 pandemic was caused by the severe acute respiratory syndrome coronavirus 2 (Sars-CoV-2). The nucleocapsid (N) protein from Sars-CoV-2 is a highly immunogenic antigen and responsible for genome packing. Serological assays are important tools to detect previous exposure to SARS-CoV-2, complement epidemiological studies, vaccine evaluation and also in COVID-19 surveillance. SARS-CoV-2 N (r2N) protein was produced in Escherichia coli, characterized, and the immunological performance was evaluated by enzyme-linked immunosorbent assay (ELISA) and beads-based array immunoassay. r2N protein oligomers were evidenced when it is associated to nucleic acid. Benzonase treatment reduced host nucleic acid associated to r2N protein, but crosslinking assay still demonstrates the presence of higher-order oligomers. Nevertheless, after RNase treatment the higher-order oligomers reduced, and dimer form increased, suggesting RNA contributes to the oligomer formation. Structural analysis revealed nucleic acid did not interfere with the thermal stability of the recombinant protein. Interestingly, nucleic acid was able to prevent r2N protein aggregation even with increasing temperature while the protein benzonase treated begin aggregation process above 55 °C. In immunological characterization, ELISA performed with 233 serum samples presented a sensitivity of 97.44% (95% Confidence Interval, CI, 91.04%, 99.69%) and a specificity of 98.71% (95% CI, 95.42%, 99.84%) while beads-based array immunoassay carried out with 217 samples showed 100% sensitivity and 98.6% specificity. The results exhibited an excellent immunological performance of r2N protein in serologic assays showing that, even in presence of nucleic acid, it can be used as a component of an immunoassay for the sensitive and specific detection of SARS-CoV-2 antibodies.

Antigen production and development of an indirect ELISA based on the nucleocapsid protein to detect human SARS-CoV-2 seroconversion

Serological assays are important tools to identify previous exposure to SARS-CoV-2, helping to track COVID-19 cases and determine the level of humoral response to SARS-CoV-2 infections and/or immunization to future vaccines. Here, the SARS-CoV-2 nucleocapsid protein was expressed in Escherichia coli and purified to homogeneity and high yield using a single chromatography step. The purified SARS-CoV-2 nucleocapsid protein was used to develop an indirect enzyme-linked immunosorbent assay for the identification of human SARS-CoV-2 seroconverts. The assay sensitivity and specificity were determined analyzing sera from 140 RT-qPCR-confirmed COVID-19 cases and 210 pre-pandemic controls. The assay operated with 90% sensitivity and 98% specificity; identical accuracies were obtained in head-to-head comparison with a commercial ELISA kit. Antigen-coated plates were stable for up to 3 months at 4 °C. The ELISA method described is ready for mass production and will be an additional tool to track COVID-19 cases.

[Conversion of serum anti-Schistosoma japonicum antibodies detected by immunological tests following treatment with praziquantel: a meta-analysis]

OBJECTIVE

To evaluate the conversion of serum antibodies against Schistosoma japonicum in humans and livestock detected by immunological tests following treatment with praziquantel.

METHODS

The studies pertaining to serological tests of schistosomiasis japonica published from 1991 to 2020 were retrieved in electronic databases, including Chinese National Knowledge Infrastructure, WanFang Data, PubMed and ScienceDirect. Data were extracted from included studies. The publication bias was assessed with funnel plots using the software RevMan version 5.3, and the conversion of antibodies against S. japonicum was evaluated through meta-analysis.

RESULTS

A total of 40 publications were included in the final meta-analysis, consisting of 33 Chinese publications and 7 English publications, and all immunological tests were performed with indirect hemagglutination test (IHA) and enzyme-linked immunosorbent assay (ELISA). Pooled analysis showed that the negative rates of serum anti-S. japonicum antibody were 45.36% [95% confidential interval (CI): (43.96%, 46.76%)] and 20.83% [95% CI: (19.69%, 21.97%)] detected by ELISA and IHA within 6 months post praziquantel treatment, 62.95% [95% CI: (61.59%, 64.31%)] and 55.61% [95% CI: (54.21%, 57.01%)] within 6 to 12 months after treatment and 85.92% [95% CI: (84.94%, 86.90%)] and 86.90% [95% CI: (85.95%, 87.85%)] over 12 months after treatment, respectively.

CONCLUSIONS

The negative rate of the serum anti-S. japonicum antibody by IHA and ELISA increased with the time of post-treatment with praziquantel. The overall negative rates of anti-S. japonicum antibody detected by IHA and ELISA are low within 12 months post praziquantel treatment. However, a high negative rate of anti-S. japonicum antibody is detected if there is no new contact with infested water after 12 months of praziquantel treatment.

A new application of plant virus nanoparticles as drug delivery in breast cancer

Nanoparticles based on non-pathogenic viruses have opened up a novel sector in nanotechnology. Viral nanoparticles based on plant viruses have clear advantages over any synthetic nanoparticles as they are biocompatible and biodegradable self-assembled and can be produced inexpensively on a large scale. From several such under-development platforms, only a few have been characterized in the target-specific drugs into the cells. Potato virus X is presented as a carrier of the chemotherapeutic drug Herceptin that is currently used as a targeted therapy in (HER2+) breast cancer patients. Here, we used nanoparticles formed from the potato virus X to conjugate the Herceptin (Trastuzumab) monoclonal antibody as a new option in specific targeting of breast cancer. Bioconjugation was performed by EDC/sulfo-N-hydroxysuccinimide (sulfo-NHS) in a two-step protocol. Then, the efficiency of conjugation was investigated by different methods, including sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blot, ELISA, Zetasizer, and transmission electron microscopy. SDS-PAGE and Western blot analysis confirmed an 82-kDa protein band that resulted from conjugation of potato virus X (PVX) coat protein (27 kDa) to heavy chain of Herceptin (55 kDa). Zeta potential values for conjugated particles, PVX, and HER were -7.05, -21.4, and -1.48, respectively. We investigated the efficiency of PVX-Herceptin to induce SK-OV-3 and SK-BR-3 cells (HER2 positive cell lines) apoptosis. We therefore counted cells and measured apoptosis by flow cytometry assay, then compared with Herceptin alone. Based on our data, we confirmed the conjugation of PVX and Herceptin. This study suggests that the PVX-Herceptin conjugates enable Herceptin to become more potential therapeutic tools.