TLR4 and COVID-19: Toll-like receptor 4 (TLR-4) appears to be one such connecting link, as the spike protein of SARS-CoV-2 (the COVID-19 causative agent) could bind with equal efficacy with ACE-2 (angiotensin-converting enzyme 2) and TLR-4 receptors of dopaminergic neurons [4,5].