CD19 and diabetes mellitus: Regardless of whether or not they had DM, patients with severe COVID-19 had lower lymphocyte counts and percentages (Fig. 7a, b), CD3+ Cell counts (Fig. 8a), CD3+ CD4+ cell counts (Fig. 8c), CD3+ CD8 + cell counts (Fig. 8e), B(CD19+) cell counts (Fig. 9a) than those with non-severe COVID-19 (all P < 0.05).