Development of Monoclonal Antibodies against the cOmpT Protein of Avian Pathogenic Escherichia coli and Identification of Epitopes Recognized by Monoclonal Antibodies

To development monoclonal antibodies against cOmpT of avian pathogenic Escherichia coli (APEC), the recombinant cOmpT of APEC origin expression plasmid pET-28a-compT was employed, and cOmpT protein with a molecular weight about 36 kD in the form of inclusion bodies was obtained after induction with IPTG, and then renatured by urea gradient dialysis. BALB/c mice were immunized with the purified cOmpT. An indirect enzyme-linked immunosorbent assay (iELISA) was developed, the optimal coating concentration of the antigen was 0.625 μg·mL^-1 and the optimal serum dilution was 1:6 400. After the fourth immunization, the spleen of immunized mice was collected for cell fusion, three monoclonal hybridomas that can secrete antibody specific to cOmpT were obtained after multiple screenings, named 1G8, 2C3 and 2G3 respectively. And all of their immunoglobulin subclasses were IgG2b. The titers of monoclonal antibodies in the cell culture supernatant were 1:200, 1:3 200 and 1:3 200 determined by iELISA, respectively. All three monoclonal antibodies were confirmed to react with cOmpT in Western blot, without cross reaction with other tested bacteria. The antigenic epitopes recognized by the three monoclonal antibodies were identified by using a series of E. coli strains harboring expression plasmids recombined with truncated fragments from compT gene. The results revealed that the antigenic epitope required for reactivity with the 1G8 was ⁸³DQDWMDS⁸⁹, and ⁹⁰SNPGTW⁹⁵, ¹⁹⁷TFKYSGW²⁰³were recognized by 2C3 and 2G3, respectively. In this study, three monoclonal antibodies against cOmpT were successfully developed and the antigenic epitopes recognized by the antibodies were identified. The cOmpT specific monoclonal antibodies obtained in this study are potentially useful tools for both the functional study of cOmpT and the development of APEC epitope vaccines.