Functional capacity of circulating CD4 + CXCR5+ T cell subsets. CD4 + CXCR5+ T cell subsets (Tfh-Th1, Tfh-Th2 or Tfh-Th17) isolated from peripheral blood of HC were co-cultured with autologous CD19 + CD27- naïve B cells for 13 days. Shown are concentrations of IgG, IgA and IgM in 13-day co-culture supernatants. Line and bar graphs represent the mean and SD of five independent experiments. Tfh-Th1 cells, CXCR5 + CXCR3 + CCR6- T cells; Tfh-Th17 cells, CXCR5+ CXCR3-CCR6+ T cells; Tfh-Th2 cells, CXCR5 + CXCR3-CCR6- T cells.