CR2 and COVID-19: DN1 (CD21+ CD11c-) B cells showed no differences between healthy subjects and mild/moderate COVID-19 patients but exhibited a significant reduction in severe and critical cases; DN2 (CD21- CD11c+) B cells only display a significant increase in severe vs. mild/moderate and critical cases while DN3 (CD21- CD11c-) fraction was by far the most altered since their frequency was seen significantly increased as disease severity increased (Figure 2H).