Fluorescein isothiocyanate conjugated anti human igm or igg antibody

The SARS-CoV-2 virus was obtained from the Korea Disease Control and Prevention Agency and was used to infect Vero E6 cells. To prepare a SARS-CoV-2 antigen slide, cells infected for 3 days were cultured on Teflon-coated multiwell slides overnight at 37°C and 5% CO₂ and were fixed with 80% acetone the next day. Each patient’s serum was subjected to 2-fold serial dilutions starting from 1:16 and then reacted with SARS-CoV-2 viral antigens in a moist chamber for 30 min at 37°C. After washing, the slides were further incubated with a 1:400-diluted secondary antibody (a fluorescein isothiocyanate–conjugated anti-human IgM or IgG antibody; MP Biomedicals, OH, USA). Then, the slides were observed under a fluorescence microscope (Olympus IX73, magnification: 400×) after the addition of mounting solution (VECTOR Laboratories, Burlingame, CA 94010, USA) on the slides. An IgG antibody titer ≥1:32 was chosen as the cutoff for the indirect immunofluorescent assay (IFA) using the clinical samples from 15 healthy individuals (34 ).

The SARS-CoV-2 virus was obtained from the Korea Disease Control and Prevention Agency and was used to infect Vero E6 cells. To prepare a SARS-CoV-2 antigen slide, cells infected for 3 days were cultured on Teflon-coated multiwell slides overnight at 37°C and 5% CO₂ and were fixed with 80% acetone the next day. Each patient’s serum was subjected to 2-fold serial dilutions starting from 1:16 and then reacted with SARS-CoV-2 viral antigens in a moist chamber for 30 min at 37°C. After washing, the slides were further incubated with a 1:400-diluted secondary antibody (a fluorescein isothiocyanate–conjugated anti-human IgM or IgG antibody; MP Biomedicals, OH, USA). Then, the slides were observed under a fluorescence microscope (Olympus IX73, magnification: 400×) after the addition of mounting solution (VECTOR Laboratories, Burlingame, CA 94010, USA) on the slides. An IgG antibody titer ≥1:32 was chosen as the cutoff for the indirect immunofluorescent assay (IFA) using the clinical samples from 15 healthy individuals (34 ).