Antibody preparation and immunological analysis of RBD from the SARS-CoV-2 Omicron BF.7 variant

The SARS-CoV-2 spike protein facilitates target recognition, cellular entry, and viral infection, leading to varying degrees of COVID-19 severity. Amino acid site mutations in the S protein RBD region can enhance the spread and immune evasion of the SARS-CoV-2 Omicron variant. The study aimed to construct a prokaryotic expression vector for the S protein RBD of the SARS-CoV-2 Omicron BF.7 variant strain. Escherichia coli was used to express the RBD protein, and a polyclonal antibody was generated to investigate the immunological functions of the Omicron (BF.7) RBD. Optimization of expression conditions in Escherichia coli was conducted to achieve stable expression of pET-28a-BF.7-RBD, including induced temperature, induced time, and IPTG concentration. Serum antibody titers in RBD-immunized mice reached up to 1: 204800 as determined by indirect enzyme-linked immunosorbent assay. The polyclonal antibody could detect prokaryotic and eukaryotic RBD proteins, as well as commercial RBD proteins, and splenocytes were found to produce high levels of IFN-γ. This study successfully demonstrated the production of a large quantity of RBD protein with strong immunogenicity in E. coli, eliciting robust humoral and cellular immune responses in mice. The generation of high-potency polyclonal antibodies provides valuable insights for further research on the biological functions of the RBD protein, detection of Omicron variants, and vaccine development.