CCL2 and COVID-19: Thus, we presented a meta-analysis of 21 studies in order to assess the association between immune cells (CD3+ T, CD4+ T, CD8+ T, Treg, B and NK cells), cytokines (TNF-α, IFN-γ, IL-2, IL-4, IL-5, IL-6 and IL-10), chemokines (GM-CSF, RANTES, MCP-1, IP-10 and eotaxin) and COVID-19 severity respectively.