Fig. 6

Spike-specific CXCR3⁺ T_FH cells exhibited higher activation status and greater IL-21 secretion than spike-specific CXCR3⁻ T_FH cells upon antigen stimulation. a–c Frequencies of HLA-DR⁺ CD154⁺, ICOS⁺ CD154⁺, PD-1⁺ CD154⁺ expression and intracellular IL-21 secretion by T_FH cells, CXCR3⁺ T_FH cells, and CXCR3⁻ T_FH cells from convalescents, vaccinees, and healthy controls upon control or antigen stimulation. d Comparison of HLA-DR⁺ CD154⁺, ICOS⁺ CD154⁺, PD-1⁺ CD154⁺, and intracellular IL-21 expression (data presented with background subtracted) among CXCR3⁺ and CXCR3⁻ T_FH cells from convalescents, vaccinees, and healthy controls, upon antigen stimulation. Frequencies of HLA-DR⁺ CD154⁺, ICOS⁺ CD154⁺, and PD-1⁺ CD154⁺ cells among T_FH cells, CXCR3⁺ T_FH cells, and CXCR3⁻ T_FH cells from convalescents (n = 16), vaccinees (n = 17), and healthy controls (n = 19) upon BSA or spike protein stimulation. Frequencies of intracellular IL-21 expression by T_FH cells, CXCR3⁺ T_FH cells, and CXCR3⁻ T_FH cells from convalescents (n = 12), vaccinees (n = 13), and healthy controls (n = 11) upon SARS-CoV-2 peptide pool stimulation. Paired t-test was used to analyze the differences between the two groups. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. P < 0.05 was considered to be a two-tailed significant difference; ns, not significant