CD40LG and COVID-19: Demers-Mathieu et al. measured the levels of SIgM/IgM, IgG and SIgA/IgA reactive to SARS-CoV-2 S1 and S2 subunits (S1 + S2) and nucleocapsid protein in BM samples collected during COVID-19 pandemic and compared them with prepandemic controls.