Similar frequency of IL-21 produced by aged and young blood CXCR5 + CD4 + Tfh cells. A. Representative results of IL-21+ cells produced by Tfh or CD4 + CXCR5-cells were shown. B. FACS data of percentages of IL-21+ cells in CD4 + CXCR5 + Tfh cells or CD4 + CXCR5- cells from both aged and young individuals (young subjects: n = 23, aged subjects: n = 23) were shown. C. IL-21 concentration determined by ELISA was shown. PBMCs were prepared and cultured with P + I (PMA and inomycin) or – (medium) for 3 days. Supernatants were collected and IL-21 was evaluated by ELISA. *: p < 0.05. All data were expressed with line at mean with SEM.