CD40LG and COVID-19: The results showed that the proportions of HLA-DR+ CD154+, ICOS+ CD154+, and PD-1+ CD154+ cells among TFH cells, CXCR3+ TFH cells, and CXCR3− TFH cells were significantly enhanced upon spike protein stimulation compared with BSA stimulation in both COVID-19 convalescents and vaccinees, except for the proportions of HLA-DR+ CD154+ in TFH cells and CXCR3− TFH cells, as well as ICOS+ CD154+ cells in CXCR3− TFH cells, from convalescents (Fig. 6a–c).