CXCR4 and COVID-19: Significantly increased percentages of CXCR4-expressing CD74+ CD4+ T cells (mean: healthy 61.5%, mild 84.0%, severe 81.0%; Figure 2F) and CXCR4 CD74+ CD8+ T cells (mean: healthy 54.2%, mild 78.4%, severe 71.7%; Figure 2F) were observed in both groups of COVID-19 patients in comparison to healthy controls.