CD4 and respiratory failure: MRC1 also has an anti-inflammatory function and induces immunotolerance.34 CCL18 (AMAC1, MIP4) is a chemokine that attracts lymphocytes, including CD4+ and CD8+ T cells, which might play a role in both humoral andcellular immune responses.35 A previous study showed that all COVID-19 patients with severe respiratory failure displayed either immune dysregulation or macrophage activation syndrome.36 Modulating macrophage activation might be a potential therapeutic strategy for severe COVID-19 patients.