Expression and serological application of recombinant epitope-repeat protein carrying an immunodominant epitope of Newcastle disease virus nucleoprotein

Gaikwad, Satish S.; Lee, Hyun-Jeong; Kim, Ji-Ye; Choi, Kang-Seuk

The optimal concentration of the rERP (1 μg/mL) and the dilution rate of sera (1:400) for indirect ELISA assays to evaluate the specificity and sensitivity of the expresses rERP were determined. To set up a cutoff value for indirect ELISA assay, 10 SPF chicken serum samples were analyzed. The mean OD450 value of these samples as measured by ELISA was 0.231 with a SD of 0.00022. For a 99% confidence interval, the cutoff value determined was 0.232 (mean OD of SPF sera samples+3 SD). Based on the cutoff value, the reactivity of rERP with chicken anti-AIV, anti-IBV, anti-IBDV, and normal sera was measured. The result showed that OD450 nm values of non-NDV sera were lower than cutoff value (Fig. 3A) . The minimum dilution titer of chicken anti-NDV serum detected was 1:1,600 according to cutoff value of 0.232 (Fig. 3B ).