Moreover, four lymphocyte subset-specific marker genes in blood including CD4 in Tregs, activated CD4+ T cells, naïve CD4+ T cells, T helper cells, CD19 in memory B cells, activated CD4+ T cells, immature transitional B cells, naïve B cells, NK cells, CCR7 in effector memory CD4+ T cells, naïve T cells, and IL7R in Tregs were significantly decreased in COVID-19 patients compared to healthy controls (Fig. 6D). Here, CD19 is linked to COVID-19.