CD4 and COVID-19: On the other hand, the inability of Th1-polarized CD4 T cells to switch towards an IL-10-producing phenotype has been shown to cause severe tissue damage in different infection models [73], and a prolonged Th1 cytokine profile has been demonstrated in the blood of patients with severe COVID-19 [60] and in the bronchoalveolar lavage during ongoing lung inflammation [69].