TLR4 and pulmonary fibrosis: The toll-like receptor 4 (TLR4) plays a crucial role in the innate immune system, cardiac hypertrophy, myocardial inflammation, lung fibrosis, atherosclerosis, skin fibroblasts, and alveolar and bronchial epithelial cells that bind with the spike-glycoprotein of SARS-CoV-2 and increases angiotensin-converting enzyme 2 (ACE 2) expression.