PTGS2 and COVID-19: The PTGS2posF3high transitional cells were characterized by expression of the secretory marker KRT23 [44], PTGS2 encoding for cyclooxygenase-2, PTGES encoding for prostaglandin E synthase, coagulation factor III (F3), and plasminogen activator inhibitor 2 (SERPINB2), which all may play roles in COVID-19 inflammatory and coagulation symptoms.