The S-UFRJ ELISA was performed using the trimeric spike protein of SARS-COV-2 produced in stable recombinant HEK293 cells as described in Alvim et al. (2022) (link) and it was provided by the Cell Culture Engineering Laboratory—LECC from the Universidade Federal do Rio de Janeiro—UFRJ. The secondary antibodies concentration used was 1:200 goat anti-human IgM (Fc) HRP-labeled antibody (#MFCD00162459; Sigma, St. Louis, MO, USA), anti-human IgG (Fc) HRP-labeled antibody (#SAB3701282; Sigma, St. Louis, MO, USA), anti-human IgE (Fc) HRP-labeled antibody (#A18793; Invitrogen, Waltham, MA, USA), and anti-human IgA (Fc) (#PA1-74495; Invitrogen, Waltham, MA, USA), incubated for 1 h at room temperature. The reaction was read at 450 nm in a Thermo Scientific Multiskan Sky microplate reader. The results were expressed either as optical density units (OD) or as the ratio of sample OD/cut-off value. The pre pandemic healthy donors (blood samples before 2019) were selected as negative controls. Then, the cut-off was made by means of O.D. of the samples plus three times the O.D. Standard deviation (Alvim et al., 2022 (link)).
Free full text: Click here