IL21 and COVID-19: However, HD patients with COVID-19 symptom worsening showed up-regulation (more than 2.5-fold increase) of GM-CSF, IFN-γ, IL-1β, IL-2, IL-6, IL-17A and IL-21, and down-regulation of TNF-α and IL-8 serum levels after the dialysis procedure (Figure 4).