IMMUNOLOGICAL ASSAY
To investigate antibody kinetics to SARS-CoV-2, we performed serial SARS-CoV-2 serological tests by chemiluminescent immunoassay using iFlash 3000 and iFlash-SARS-CoV-2 IgG/IgM/IgA kits (Shenzhen YHLO Biotech Co., Ltd., Shenzhen, China). The serum IgG, IgM, and IgA antibodies against S1, RBD, and N were quantified. The patient’s blood samples collected on days -8 (during a regular checkup), 1, 2, 4, 6, 9, 32, 59, 79, 100, and 136 were examined. The cutoff values used were based on the results of 249 samples collected from the University of Tokyo Hospital (137 samples from SARS-CoV-2 RNA-positive patients and 112 samples from SARS-CoV-2 RNA-negative patients).
The anti-S1 and anti-RBD IgA levels exceeded the cutoff levels on day 9 and rapidly decreased thereafter. The anti-N IgM level was elevated on day 32. The anti-S1 IgG and IgM and the anti-N IgG levels also increased, but their titers did not exceed the cutoff values. Meanwhile, the anti-RBD IgG and IgM levels hardly changed (Fig. 2).