CD4 and COVID-19: Additionally, increased frequencies of virus-specific cTfh cells (CD4+CXCR5+OX40+CD40L+) were observed in acute and convalescent COVID-19 cases, and the frequencies of both SARS-CoV-2-specific cTfh cells and S-specific CCR6+CXCR3-cTfh17 cells were closely associated with low disease severity (151).