Preparation and characterization of monoclonal antibodies against BP26 protein of Brucella melitensis M5-90

Abstract

Objective To prepare high specific monoclonal antibodies(mAbs) against BP26 of Brucella(B.)melitensis.Methods A recombinant plasmid pET-28a-BP26 was constructed and transformed into competent Escherichia coli BL21 (DE3),and then the bacteria were induced by 1 mmol/L isopropylthio-β-D-galactoside (IPTG).After induction,the recombinant BP26 protein (rBP26) was purified by sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PGAE) and nickel ion affinity chromatography(Ni-NTA).Mice were inoculated with rBP26 antigens for three times at 2-week intervals.The first subcutaneous injection contained 100 μg rBP26 with 0.1 ml complete Freund adjuvant.The second subcutaneous injection was 50 μg rBP26 with 0.1 ml incomplete Freund adjuvant.The antibody titers to rBP26 were determined 2 weeks after each reimmunization.Three days before cell fusion,the mice with the highest titer were intraperitoneally injected with 50 μg rBP26 in 0.1 ml PBS.Pre- and post-immunization sera were collected and used as negative or positive controls for screening mAbs.Mice with the highest titer were sacrificed and spleen cells were isolated.The spleen cells of rBP26 immunized mice were fused with SP2/0 myeloma cells in a ratio of 5 ∶ 1 by polyethylene glycol(PEG) 1450.Antibody-producing hybridomas were primarily screened by an indirect enzyme-linked immunosorbnent assay(ELISA) with rBP26.Reactive hybridomas were subcloned for 3 times,then the strains of hybridoma cells secreting antibodies against BP26 were obtained.Supernatant of cloned hybridoma cultures was collected for mAb analyses.These mAbs were named by the hybridoma clone number and tested their reactivity to membrane proteins extracted(NMP) from B.melitensis vaccine strain(M5-90) by Western blotting and Dot-ELISA.mAbs isotyping and kappa(κ) or lambda(λ) light chain was identified by Mouse Monoclonal Antibody Isotyping Kit.Results A total of two mAbs reactive to rBP26 of B.melitensis were selected from antibody screening hybridomas by indirect-ELISA.The two mAbs were named 3C3 and 5A5,and identified as IgG1 (κ) and IgG2(κ),respectively.They could react with NMP from M5-90.Conclusions Results of identification show that two mAbs against rBP26 can be produced.The two mAbs can recognize natural BP26 protein,giving the experimental materials for further research on identification of its epitopes. Key words: Brucella melitensis; Periplasmic protein BP26; Antibodies, monoclonal