IL6R and COVID-19: To functionally test the role of cytokines on the viability of lymphocytes, we treated PBMCs isolated from healthy donors with selected groups of cytokines (e.g., IL-10, IL-15, IL-18, IL-8, IL-6, IL-1RA, IL-2RA, IL-4) for 36 h, using the maximum doses detected in COVID-19 serum.