Compared to non-COVID-19, COVID-19 patients displayed higher levels of RBD IgM (p = 0.0019) and IgG (p = 0.0004) in respiratory samples (Fig. 3a, b), but not RBD IgA levels, which was possibly due to either technical issues or cross-reactivity of IgA antibodies (Fig. 3bi). This evidence concerns the gene CD40LG and COVID-19.