Case Report: IL-21 and Bcl-6 Regulate the Proliferation and Secretion of Tfh and Tfr Cells in the Intestinal Germinal Center of Patients With Inflammatory Bowel Disease oleh Youguang Yang, Xiaodan Lv, Lingling Zhan, Lan Chen, Hui Jin, Xinping Tang, Qingqing Shi, Qiyuan Zou, Jiqiao Xiang, WeiWei Zhang, Zhaojing Zeng, Haixing Jiang, Xiaoping Lv