Fig.5. Validation of the S-iELISA by IFA.
(A) Identification of SADS-CoV-negative and positive sera by IFA. IPI-FX cells were seeded on 24-well plates and cultured overnight, followed by infection with SADS-CoV at a MOI of 0.01. Mock-inoculated IPI-FX cell culture showing normal cells. SADS-CoV-inoculated IPI-FX cells at 1 d.p.i. showing syncytium (indicated by arrows). At 24 hour postinoculation, cells were fixed and probed with 111 pig serum samples containing SADS-CoV-negative, weakly positive, strongly positive serum samples and 1 × PBS, SADS-CoV Ab (-) serum, SADS-CoV Ab (+) serum as controls, followed by incubation with Cy3-conjugated rabbit anti-pig antibodies (red). Cell nuclei were counterstained with DAPI (blue). Cells were observed with a fluorescence microscope. The scale bar represents 100 μm. (B) The specificity and sensitivity of the S-iELISA were analyzed based on the results of IFA.
Fig.6. Determination of the correlation between SADS-CoV virusneutralization titers and OD450nm values of S-iELISA.
Seven serum samples were tested by S-iELISA and virus neutralization assays, respectively. The OD450nm values and neutralizing antibody titers were compared to determine the relationship between S-iELISA and the neutralizing antibody of SADS-CoV.