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).