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BACKGROUND The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants can infect common mice inducing significant pathological lung lesions and inflammatory responses. This substantially mimics coronavirus disease 19 (COVID-19) infection and pathogenesis in humans. OBJECTIVES To characterise the effects of recombinant SARS-CoV-2 S1 receptor-binding domain (RBD) peptide in murine macrophage and microglial cells' immune activation compared with classical PAMPs in vitro. METHODS Murine RAW 264.7 macrophages and BV2 microglial cells were exposed to increasing concentrations of the RBD peptide (0.01, 0.05, and 0.1 µg/mL), Lipopolysaccharide (LPS) and Poly(I:C) and evaluated after two and 24 h for significant markers of macrophage activation. We determined the effects of RBD peptide on cell viability, cleaved caspase 3 expressions, and nuclear morphometry analysis. FINDINGS In RAW cells, RBD peptide was cytotoxic, but not for BV2 cells. RAW cells presented increased arginase activity and IL-10 production; however, BV2 cells expressed iNOS and IL-6 after RBD peptide exposure. In addition, RAW cells increased cleaved-caspase-3, apoptosis, and mitotic catastrophe after RBD peptide stimulation but not BV2 cells. CONCLUSION RBD peptide exposure has different effects depending on the cell line, exposure time, and concentration. This study brings new evidence about the immunogenic profile of RBD in macrophage and microglial cells, advancing the understanding of SARS-Cov2 immuno- and neuropathology.
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@#ObjectiveTo construct and identify a recombinant adenovirus expressing S protein receptor binding domain(RBD)and N protein of severe acute respiratory symptom coronavirus 2(SARS-CoV-2)Delta variant.MethodsThe RBD and N gene fragments of SARS-CoV-2 were cloned into pcDNA3.0BA vector respectively to construct recombinant plasmid pcDNA3.0BA-RBD-N. The RBD-CMV-N fragment was amplified by PCR and inserted into shuttle vector pShuttle-CMV. The shuttle plasmid pShuttle-RBD-N was then homologously recombined with pAdeasy-1 to obtain recombinant plasmid pAdeasy-1-RBD-N,which was transfected into HEK293 cells for recombinant adenovirus Ad-RBD-N packaging. The transcription of RBD and N genes of recombinant adenovirus in HEK293 cells was detected by RT-PCR,while the expre-ssion of RBD and N proteins by Western blot and immunofluorescence assay. 12 female BALB/c mice were immunized with Ad-RBD-N by intramuscular injection at a dose of 5 × 109copies per mouse. Blood samples were collected 14 d after immunization,and the serum antibody titers were measured by ELISA.ResultsThe RBD and N genes of recombinant adenovirus were transcribed normally in HEK293 cells,and the RBD and N proteins were expressed normally in MA104 cells. Mice immunized with the recombinant adenovirus produced specific IgG antibodies against RBD and N proteins.ConclusionThe recombinant adenovirus expressing S protein RBD and N protein of SARS-CoV-2 Delta variant was succe-ssfully constructed,which laid a foundation of the follow-up research on Delta variant vaccines.
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@#Objective To construct a single-chain fragment variable(scFv)phage display library against receptor-binding domain(RBD)of severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)spike protein(S)to screen specific scFv and identify the function.Methods m RNA was extracted from spleen cells of mice immunized with RBD protein and reversely transcribed into c DNA,with which as template,genes of the hight chain fragment of variable(VH)and light chain fragment of variable(VL)of scFv were amplified and then assembled into scFv gene fragment through splicing overlap extension PCR(SOE-PCR).The scFv gene fragment was inserted to phage vector to construct scFv phage display library.After four rounds of biopanning,the scFv gene with strong binding ability to RBD was screened and expressed recombinantly,purified and identified for biological activity.Results The constructed scFv phage library showed a titer of 6.0×10(11)pfu/m L.After four rounds of biopanning,four scFv strains with strong binding to RBD were selected,namely scFv11,scFv12,scFv25and scFv28.scFv was mainly expressed in the form of inclusion body with a relative molecular mass of about 27 000,a concentration of 2.4 mg/m L and a purity of about 90%,which bound specifically to mouse monoclonal antibody against His labeled by HRP after purification.All four scFv strains bound specifically to RBD recombinant protein,among which the other 3 scFv strains bound to the S protein of wild type and multiple mutant strains except scFv28.All four strains showed dose-dependent interaction with RBD,with affinity dynamic fitting dissociation constants(K_Ds)8.9,5.92,10.67and 2.36 nmol/L,and steady-state fitting dissociation constants(K_Ds)of 5.3,6.5,8.7 and 5.8 nmol/L,respectively.scFv11,scFv12 and scFv25 simultaneously identified three independent RBD polypeptides,including RBD2(S(11)pfu/m L.After four rounds of biopanning,four scFv strains with strong binding to RBD were selected,namely scFv11,scFv12,scFv25and scFv28.scFv was mainly expressed in the form of inclusion body with a relative molecular mass of about 27 000,a concentration of 2.4 mg/m L and a purity of about 90%,which bound specifically to mouse monoclonal antibody against His labeled by HRP after purification.All four scFv strains bound specifically to RBD recombinant protein,among which the other 3 scFv strains bound to the S protein of wild type and multiple mutant strains except scFv28.All four strains showed dose-dependent interaction with RBD,with affinity dynamic fitting dissociation constants(K_Ds)8.9,5.92,10.67and 2.36 nmol/L,and steady-state fitting dissociation constants(K_Ds)of 5.3,6.5,8.7 and 5.8 nmol/L,respectively.scFv11,scFv12 and scFv25 simultaneously identified three independent RBD polypeptides,including RBD2(S(334～353)),RBD9(S(334～353)),RBD9(S(439～458))and RBD13(S(439～458))and RBD13(S(499～518)).Homologous model of scFv constructed by online server SWISS-MODEL showed a good quality and was used for molecular docking.The interface at which scFv11 interacted with RBD only partially coincided with the interaction interface of human angiotensin converting enzyme 2(ACE2)and RBD,and the interaction interfaces of scFv12 and scFv25 with RBD were quite different from that of ACE2.Conclusion In this study,scFv specifically bound to SARS-Co V-2 RBD was screened and prepared through constructing scFv phage library against SARS-CoV-2 RBD,which provided experimental basis for further development of anti-SARS-CoV-2 drugs and detection reagents.
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Objective@#To establish an indirect enzyme-linked immunosorbent assay (ELISA)and to compare the efficiency of receptor binding domain (RBD) proteins in different forms for Middle East respiratory syndrome coronavirus (MERS-CoV) antibody detection.@*Methods@#The monomeric and trimeric forms of MERS-CoV RBD were expressed in Bac-insect cells, 293T cells and ExpiCHO-S™ expression system and then purified. The purified RBD proteins were identified with native gel electrophoresis and Western blot. Then, an equal amount of each RBD protein was used as coating antigen to establish an ELISA for detecting MERS-CoV IgG titer. For comparison, the newly developed ELISA and the commercial MERS-CoV IgG antibody detection kit (Euroimmune with S1 as the coating antigen) were used to measure the MERS-CoV antibody reference panel supplied by World Health Organization (WHO).@*Results@#The purified monomeric and trimeric MERS-CoV RBD were successfully prepared using 293T cells and ExpiCHO-S™ system. RBD antigens of different forms and from different systems could recognize MERS-CoV specific antibody without having any cross reaction with the sera from healthy adults. The in-house RBD-based ELISA had good detection consistency with the Euroimmune commercial kit. The positive samples showed higher and more concentrated values based on the RBD trimer than the monomer.@*Conclusions@#Novel indirect ELISA methods based on the monomeric and trimeric forms of RBD protein were established. The trimetric form-based ELISA achieved higher detection efficiency than the one using the monomer antigen, suggesting that it could be uses as a competent alternative to the commercial kit.