CD40LG and COVID-19: Likewise, circulating spike- and RBD-IgA titers strongly correlated with NT50 values (r=0.65 p<0.00001 and r=0.6 p<0.00001, respectively) (Figures 2A, B), suggesting that RBD-specific IgM and IgA titers significantly contribute to SARS-CoV-2 neutralization, at least during the early convalescence of COVID-19 outpatients.