Fig. 1.

CXCR5⁻PD-1^hi Tph and CXCR5⁺PD-1^hi Tfh CD4⁺ memory T cell subsets share features associated with B cell helper function. (a) A representative flow cytometric staining of peripheral blood memory T cells (gated as CD3⁺CD4⁺CD45RA⁻) subdivided into CXCR5⁻ (red) and CXCR5⁺ (blue), and further into PD-1⁻, PD-1^int and PD-1^hi subsets. (b–n) The expression of different surface markers (b–i) and the proliferation marker Ki67 (j), the production of cytokines after PMA and ionomycin stimulation (k–m) and the capacity to induce memory B cell differentiation to plasma cells in a co-culture of the different subsets (n). The results are expressed as mean ± SEM geometric mean fluorescence intensity (MFI) values or percentage positive from four to eight experiments, each performed with cells from different healthy donors. For cytokine production and B cell co-culture experiments, the T cell subsets were flow-cytometrically sorted before the analyses. *p<0.05, **p<0.01 and ***p<0.001 compared with naive CD4⁺ T cells (grey bars), or CXCR5^–PD-1^hi vs CXCR5⁺PD-1^hi subsets where indicated; Kruskal–Wallis test with Dunn’s post hoc test