CD4 and COVID-19: Our meta-analysis revealed significantly lower levels of immune cells (CD3+ T, CD4+ T, CD8+ T, B and NK cells), higher levels of cytokines (TNF-α, IL-5, IL-6 and IL-10) and higher levels of chemokines (MCP-1, IP-10 and eotaxin) in severe cases in comparison to mild cases of COVID-19.