Extended Data Fig. 9: SARS-CoV-2 spike-specific Tfh cell response after antigen stimulation.

Representative flow plots of the antigen specific Tfh cells after stimulation. To determine the expression of CD154 (a) and OX40 and CD25 (b), PBMCs from COVID-19 individuals and healthy controls were stimulated with SARS-CoV-2 spike subunits S1 and S2, or BSA. Con A and SEB were used as positive controls. After stimulation, surface CD154 and both OX40 and CD25 were measured by flow cytometry gating on PD-1⁺ CXCR5⁺ CD4⁺ T cells. For intracellular cytokine secretion, PBMCs from COVID-19 individuals and healthy controls were stimulated with SARS-CoV-2 spike subunits S1 and S2, or BSA, in the presence of anti-CD28, anti-CD49d. Anti-CD3 was as positive control. After stimulation, intracellular IL-21 (c) and IFN-γ (d) were measured by flow cytometry gating on PD-1⁺ CXCR5⁺ CD4⁺ T cells. The gating of cell populations was based on the mean fluorescence intensity ‘minus one’ (FMO).