These included anti-dsDNA concentration, expression of type I IFN signature genes, and the frequency of IgD and CD27 ‘double-negative’ (DN) B cells lacking CD21 expression but expressing CD11c (DN2 cells), which expanded in patients with active SLE and correlated with increased morbidity in COVID-19 patients (18, 19). Here, CD27 is linked to systemic lupus erythematosus.