The number of T lymphocyte subsets, including naïve T4/T8 cells, central memory T4/T8 cells, PD1+ depletes T8 cells, and effector memory T8 cells, was moderately increased in COVID-19 patients with normal IL-6 levels, and with increasing IL-6 levels, these lymphocyte subset counts declined (Fig. 5A). Here, IL6 is linked to COVID-19.