Analysis of IgM, IgA, and IgG Isotype Antibodies Directed Against SARS‑CoV‑2 Spike Glycoprotein and ORF8 in the Course of COVID‑19.

Abstract

Immunoassays are a standard diagnostic tool assessing immunity in severe acute respiratory syndrome coronavirus type 2 (SARS‑CoV‑2) infection. However, immunoassays do not provide information about contaminating antigens or cross‑reactions and might exhibit inaccurately high sensitivity and low specificity. We aimed to gain insight into the serological immune response of SARS‑CoV‑2 patients by immunoblot analysis.We analyzed serum immunoglobulins IgM, ‑A, and ‑G directed against SARS‑CoV‑2 proteins by immunoblot analysis from 12 infected patients. We determined IgG isotype antibodies by commercially available ELISA and assessed the clinical parameters of inflammation status and kidney and liver injury.We found evidence for antibody cross‑reactivity, which calls into question a reliable assessment of serum samples tested negative for anti‑SARS‑CoV‑2 antibodies by immunoassays. Nevertheless, for the detection of IgG anti‑SARS‑CoV‑2 antibodies, our data suggest that the use of the spike glycoprotein in immunoassays should be sufficient to identify positive patients. Using a combination of the spike glycoprotein and the open reading frame 8 protein could prove to be the best for the detection of patients positive for anti‑SARS‑CoV‑2 IgM antibodies. We found that the antibody response alone is not decisive for the course of the disease, but inflammation parameters are promising indicators.