The inlA ORF was amplified from the genomic DNA of L. monocytogenes (ATCC 19114) by PCR using an Eppendorf thermocycler (Mastercycler EP gradient S) with the following standardized conditions 94°C for 7 min, 94°C for 1 min, 45°C for 1 min, 68°C for 2 min, and a final extension of 68°C for 7 min. The amplicon was digested with BamHI and KpnI and learn more ligated into pAE—predigested
with the same enzymes—using T4 DNA Ligase (Invitrogen). The pAE-inlA construct was electrotransformed into Escherichia coli Top10 (Invitrogen), the recombinant clones were selected on LB agar containing ampicillin (100 μg/mL), and insertion of inlA (pAE-inlA) was confirmed by sequencing. The pAE-inlA plasmid was transformed into E. coli BL21(DE3) pLysS (Invitrogen) selleck inhibitor competent cells. The transformed cells were grown to reach the log phase (OD600 = 0.5–0.7) and induced with 1 mM IPTG for 3 h at 37°C. Cells were harvested, suspended in lysis buffer (100 mM NaH2PO4, 10 mM Tris HCl, and 20 mM imidazole; pH
8.0) and sonicated (3 cycles using a Branson selleck chemicals llc Sonifier). The recombinant InlA (rInlA) containing a poly-histidine tag (6×-His) was purified by using a Ni-NTA affinity chromatography system (GE Healthcare, Piscataway, NJ). Finally, column-eluted proteins were dialyzed against 0.02 M phosphate buffered saline (PBS; pH 7.2) for 24 h and concentrated with polyethylene glycol (MW 20,000). Immunization, MAb production, and MAb characterization Six-week-old BALB/c female mice were administered intraperitoneally (i.p.) with approximately 1 × 108 cells/mL of heat-killed L. monocytogenes serotype 4b diluted in PBS and mixed (1:1) with complete Freund’s adjuvant (CFA). Two weeks later, a mixture of heat-killed L. monocytogenes and 50 μg of rInlA prepared with incomplete Freund’s adjuvant (IFA) was administered i.p. every week for 8 weeks. Four days before the last immunization, the mouse showing the highest antibody titer against rInlA in an indirect ELISA received booster immunizations with rInlA via both intravenous and i.p. routes. The splenocytes were harvested from the mouse and fused with murine
Sp2/O-Ag14 myeloma cells in the presence of 50% (w/v) PEG 1450 (Sigma) as described previously . Selected hybridoma clones were administered to pristane-primed mice to produce ascitic fluid for antibody production (28). MAbs were purified by affinity chromatography using very a protein A-Sepharose 4B column (GE Healthcare), and the class and subclass of each MAb were determined by ELISA using a Mouse Subisotyping Kit (Sigma). Indirect ELISA was performed to determine the reactivities of MAbs with live bacterial cultures adjusted to OD600 = 1 (approx. 109 CFU/mL) in 0.1 M sodium carbonate coating buffer (pH 9.6) or with rInlA (10 ng/well) for 16 h at 4°C, and immunoassay was carried out as described previously . Protein preparation, SDS-PAGE, and Western blot Bacterial proteins were prepared according to the published method  with some modifications.