Figure 5. Generation of T_FH cells requires IL-6 and STAT3.

IL-6 KO (A) or STAT3 T-cell specific KO mice (C) and their appropriate controls (WT, 3 mice per group) were immunized subcutaneously with KLH emulsified in CFA. Seven days after the immunization, experimental mice were sacrificed and T_FH cells and the germinal center B cells were analyzed. Numbers in dot plot quadrants represent the percentages. (B) C57BL/6 mice were immunized with KLH in CFA. 7 days later, CD4⁺CD44^hiCXCR5⁺ and CD4⁺CD44^hiCXCR5^- cells were sorted and restimulated with anti-CD3 and anti-CD28 with or without IL-6 or IL-21 for 48 hours. Proliferation was assayed by adding [³H]-thymidine to the culture for the last 8 h. P values were calculated with the t-test by comparing the CXCR5+ cells proliferation in the absence and in the presence of IL6 (*p<0.005) or in the absence and in the presence of IL21 (*p<0.005). CD4⁺CD44^hiCXCR5⁺ and CD4⁺CD44^hiCXCR5^- cells were restimulated with anti-CD3 and anti-CD28 for 24 hours and stained with Annexin V-FITC. The experiments were performed two times with consistent results.