Publication date: Jul 01, 2023

A cost-effective and eco-friendly method is needed for the assessment of humoral immunity against SARS-CoV-2 in large populations. We investigated the performance of an ELISA that uses silkworm-produced proteins to quantify the strain-specific anti-Spike IgG (anti-S IgG) titer. The OD values for the anti-His-tag antibody, a standard material of ELISA quantification, were measured. Correlations between the ELISA for each strain and the Abbott SARS-CoV-2 IgG II Quant assay for the wild type were evaluated with serum samples from nine participants with various infection and vaccination statuses. Linear dose-responses were confirmed by high coefficients of determination: 0. 994, 0. 994, and 0. 996 for the wild-type, Delta, and Omicron (BA. 1) strain assays, respectively. The coefficient of determination for the wild-type and Delta strain assays was high at 0. 959 and 0. 892, respectively, while the Omicron strain assay had a relatively low value of 0. 563. Booster vaccinees showed similar or higher titers against all strains compared to infected persons without vaccination. The Omicron-infected persons without vaccination had lower antibody titers against wild type than did the vaccinated persons. This study provides data indicating that the ELISA with silkworm-produced proteins makes it possible to discriminate and quantify the strain-specific anti-S IgG antibody induced by vaccination or infection.

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Original Article