Figure 4.

Memory PD-1^hiCD8⁺ T cells promote the differentiation of B cells to plasmablasts and IgG production in an IL-21-dependent manner. (A) Upon stimulation of PBMCs from HCs with CD3/28 beads for 72 h, CD45RA⁺CD8⁺ T cells, CD45RA^- PD-1^hi CD8⁺ T cells and CD45RA^- PD-1^hi CD4⁺ T cells were purified by flow cytometry. Memory B (CD19⁺CD20⁺CD27⁺) cells were co-cultured with CD45RA⁺ CD8⁺ T cells, CD45RA^-PD-1^hi CD8⁺ T cells and CD45RA^- PD-1^hiCD4⁺ T cells in the presence of anti-BCR, CD3/28 beads and CpG for 6 days. Representative data on the expression of CD27 and CD38 are depicted in (A) and the results are summarized in (B) (N=4). (C) Comparison of IgG production from plasmablasts induced by co-cultured CD45RA^-PD-1^hiCD4⁺ T cells and CD45RA^-PD-1^hiCD8⁺ T cells. (D) Effect of IL-21 blockade on the frequency of plasmablasts and IgG production induced by co-cultured CD45RA^-PD-1^hiCD8⁺ T cells. *P < 0.05, **P < 0.01. un, undetected.