While increased TGF-β1 levels in the serum are in agreement with human clinical data and proposed to promote fibrosis [57], reduced levels of testicular TGF-β1, which regulates spermatogenesis and immune homeostasis pathways in the testis [58], may also be one of the underlying mechanisms of compromised testicular function in recovering COVID-19 patients. This evidence concerns the gene TGFB1 and COVID-19.