Yes, indirect ELISA could be good. You can use a virus-positive mouse serum sample as a reference standard (better a pool of positive sera) and express your concentrations as arbitrary units (AU). You have to create a reference standard curve in each assay with the same standard. for example positive serum undiluted (=100 AU), 1:2 diluted (=50 AU), 1:4 diluted (=25AU), 1:8 diluted (12.5 AU) etc. The upper and the lower OD value obtained respectively for the highest and lowest concentrations of standard must be between 2.0 and 0.2 OD. In this way you have a reference standard curve in each assay. You can generate a Reference curve in each assay using the standard serial dilutions by plotting the standard well concentrations, expressed as arbitrary units (AU), versus the OD values. In this way you can obtain the concentrations of specific antibodies in any sample by extrapolating the concentrations from the standard curve and multiplying the value for the dilution factor (if the sample was diluted). Please, look at the materials and methods section of the attached article. I hope to be clear and helpful. best whishes. massimiliano

Thank you so much.