Therefore, we compared circulating cytokine levels in Mexican patients without COVID-19 (non-COVID-19, due to unrelated causes) and with moderate, severe, and critical COVID-19 pneumonia by quantifying several proinflammatory cytokines including IL-2, IL-4, IL-6, IL-8, IL-10, TNF-α, GM-CSF, and IFN-γ. Here, IL6 is linked to COVID-19.