[Development and characterization of monoclonal Antibody against M-like protein of Streptococcus equi subsp. zooepidemicus from pig].

Streptococcus equi subsp. zooepidemicus belongs to lancefield group C streptococcus, which can cause disease both in animals and humans. It has been associated with a wide variety of serious infections, including meningitis, pneumonia, septic arthritis and mastitis. The M like proteins on the surface of S. equi subsp. zooepidemicus have an antiphagocytic role analogous to that of group A streptococcal M proteins that are essential in establishing infection. In the present study, the M-like gene without partial signal peptide sequence was amplified from genomic DNA of S. equi subsp. zooepidemicus ATCC35246 strain isolated from pig by polymerase chain reaction (PCR). Then the amplified fragment was cloned in the proper orientation into the site between EcoR I and Xho I of pET32-a(+) via restriction endonuclease EcoR I and Xho I. The recombinant plasmid was verified by restriction endonuclease analysis and nucleotide sequencing, then transformed into E. coli BL21. An fusion protein was expressed in BL21 after induced by IPTG, SDS-PAGE analysis showed that the recombinant protein had a molecular weight of 60 kD, Western blotting showed a positive reaction with the antiserum against ATCC35246. To prepare the monoclonal antibodies (McAbs) against the M-like protein, 6-8 weeks old BABL/c mice were immunized endermicly with purified recombinant M-like protein by Ni-nitrilotriacetic acid affinity chromatography. Splenocytes from the immuniszed mice were fused with SP2/0 and indirect ELISA was used to screen hybridoma cells. 12 hybridoma cell lines secreting McAbs against M-like protein of Streptococcus equi subsp. zooepidemicus were generated, and indirect ELISA confirmed that these McAbs only reacted with M-like protein, but not reacted with other bacteria such as group A Streptococci, Streptococcus suis type 2, Streptococcus equi. The indirect ELISA titers of these 12 ascites McAbs were about 2.56 x 10(4) to 1.01 x 10(5) , and the subtype of these McAbs belong to IgG2b, IgG1, IgM. The results of adhersion inhibition showed McAbs 2C8 could inhibit the adhersion of M-like protein to HEp-2 cell.