CD4 and severe acute respiratory syndrome: However, the cytokine-based endotypes of critically ill COVID-19 patients who are insensitive to treatment with steroids because of an increased concentration of the highly proinflammatory cytokine IL-17A produced by CCR4+CCR6+ Th17 in CD4+ T cells [63,64] would be quite different from those of SARS patients for whom steroid treatment is beneficial because of the increased presence of type 2 cytokines [65,66].