ACE2 and COVID-19: Although the pathophysiology of long COVID is incompletely understood, several theories have been posited to explain the molecular root of immune dysregulation, including DNA replication by viral proteins, systemic manifestation, and multiorgan involvement of COVID-19 due to broad expression of the SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2), activation of immune cells, release of autoantigens from infected tissue, superantigen-mediated activation of lymphocytes, and epitope spreading.