CD40LG and COVID-19: IgG, IgM, and IgA levels against the whole spike protein (WSP) and S1 domain (S1) of SARS-CoV-2 were measured by enzyme-linked immunosorbent assay (ELISA) using the following kits: coronavirus disease (COVID-19) Human IgM IgG ELISA kit (Spike protein); COVID-19 Human IgA ELISA kit (Spike protein, Full-Length) for WSP; COVID-19 Human IgM IgG ELISA kit (Spike protein, S1); and COVID-19 Human IgA ELISA kit (Spike protein, S1) (Cellspect Co., Ltd., Morioka, Japan) for S1.