CXCL12 and COVID-19: Furthermore, a clear clustering of cytokines (IL-6, TNF-α, IFN-γ, IFN-α, SDF-1α, MIP-1α, MIP-1β, G-CSF, IL-10, CX3CL1 and IL-4) was observed in a PCA for critically ill COVID-19 patients during the first wave who presented a bacterial superinfection during their stay at the ICU (Fig 7B).