CD40LG and COVID-19: The estimated seroprevalence was about 5% in Spain (by point-of-care lateral-flow assay for anti-SARS-CoV-2 IgM/IgG and chemiluminescentmicroparticle immunoassay for IgG) [3] and up to 11% in Geneva (by another commercially available ELISA IgG test) [24], both countries with a several-fold higher per capita COVID-19 prevalence in the general population compared to Poland.