Diagram shows how pathogenetic evolution of COVID-19 pneumonia correlates
with clinical and imaging features and management. The early infection stage
occurs at the time of inoculation. During this stage, SARS-CoV-2 binds to
its target using the angiotensin-converting enzyme 2 (ACE2) receptor and
transmembrane protease serine 2 (TMPRRS2) and multiplies in the host cells.
In the second stage, the pulmonary phase, viral multiplication and localized
inflammation in the lungs occur and viral pneumonia is developed. In a
minority of patients with COVID-19, the disease may progress to the most
severe stage, the hyperinflammatory phase. An uncontrolled systemic
inflammatory response resulting from the cytokine storm occurs at this
stage. Pink triangle indicates inflammatory response, blue triangle
indicates viral response, and black line indicates clinical severity. Areas
under trigon represent chronological changes in the intensity of responses.
Ag = antigen, ARDS = acute respiratory distress syndrome, CRP = C-reactive
protein, DIC = disseminated intravascular coagulation, IL-6 = interleukin-6,
NT-proBNP = N-terminal prohormone of brain natriuretic
peptide.