TGFB1 and pulmonary fibrosis: TGF-β is a key cytokine in regulating chronic immune reaction in severe COVID-19 and is known to play a crucial role in the development of some peculiar clinical manifestations of the infection, including fatigue, loss of olfactory and taste senses, and in the development of the detrimental pulmonary fibrosis [81,82,83,84,85].