CXCR4 and COVID-19: Values of CD74+ CD8+ T cell frequencies expressing CXCR4+ were considerable variable in both groups of infected patients and only frequencies of CXCR4-expressing E CD74+ CD8+ T cells from COVID-19 patients showed significant increases compared to the healthy controls (healthy: 24.6%, mild: 31.8%, severe: 46.0%; Figure 5B, lower panel).