However, our recent study [44] demonstrated no significant difference in titers of IgG, secretory IgM (SIgM)/IgM, and secretory IgA (SIgA)/IgA specific to SARS-CoV-2 receptor-binding domain (RBD) between COVID-19 PCR and the viral symptoms suggestive of COVID-19 groups. This evidence concerns the gene CD40LG and COVID-19.