CR2 and COVID-19: DN1 B cells (CD21 + CD11c-) were significantly reduced in severe and critical cases, but not in mild/moderate ones, compared with healthy subjects; DN2 B cells (CD21–CD11c+) were significantly increased in severe, mild/moderate, and critical cases; the DN3 (CD21–CD11c–) subset increased along with escalating disease severity; and the DN4 subset was not determined in peripheral blood samples from either COVID-19 or healthy subjects (68, 69).