5% bovine serum albumin; ELISA buffer) and incubated. Bound IgG antibodies were detected by adding 50 μL/well of peroxidase-conjugated anti-mouse IgG (1:2000 in ELISA buffer) and incubated at 37°C for 1 hr. The color reaction was developed by adding 100 μL/well of o-phenylenediamine dihydrochloride (Sigma, St Louis, MO, USA) in the presence of 0.07% H2O2 for 30 min at room

temperature, and the absorbance at 450–620 nm was measured. The MDV3100 nmr results for each serum sample were reported as the positive–negative difference (P–N), that is, the difference of the optical density (OD) with the positive antigen to the OD with the negative antigen; NusA -Tag protein was expressed from E. coli. Rabbit anti-TBE virus E protein IgG (23) was coated onto 96-well microplates (50 μL/well, 5 μg/mL in carbonate buffer). After overnight incubation at 4°C, the plates were washed five times with PBST. A blocking solution was applied (200 μL/well) and the plates were incubated at 37°C for 1 hr. The plates were washed before adding the SP antigen (50 μL/well, 1:150 dilution in ELISA buffer) and incubated at 37°C for 1 hr. After washing with PBST, the serum samples were added in duplicate (50 μL/well, 1:100 dilution in ELISA buffer)

and incubated at 37°C for 1 hr. Bound IgG antibodies were detected by adding 50 μL/well of ALP-conjugated anti-mouse IgG (1:5000 in ELISA buffer) and incubating at 37°C for 1 hr. The color reaction was developed by adding 100 μL/well of p-nitrophenyl phosphate and

incubating at 37°C for 60 min, and the absorbance D-malate dehydrogenase at 405–620 nm was measured. The results for each serum sample were reported as the P–N, that GSK3235025 is, the difference of the OD with the positive antigen to the OD with the negative antigen, which was prepared from the supernatant of non-transfected 293T cells. The OD values of each ELISA were compared with the results of the neutralization test. The sensitivity and the specificity of the ELISA were calculated corresponding to each cut-off value. The sensitivity was the ratio of the number of positive sera for ELISA and the neutralization test to the number of positive sera for the neutralization test. The specificity was the ratio of the number of negative sera for ELISA and the neutralization test to the number of negative sera for the neutralization test. The cut-off value that showed the minimum difference between the sensitivity and the specificity was used as the cut-off value of each ELISA. To prepare the recombinant antigen, we first attempted to express the whole E proteins of the TBE virus in E. coli, but the proteins were expressed as insoluble proteins and could not be applied to the ELISA (data not shown). Next, domain III of the E protein of the Oshima 5–10 strain was expressed as a fused protein with NusA -Tag protein (EdIII). To confirm and characterize the EdIII antigen, expressed proteins were analyzed by SDS-PAGE and Western blot (Fig. 1).