Germinal centers are dynamically organized tissue micro-domains in which humoral memory is generated. In LDI, we strive to understand how T cell help and T-B interactions critical for GC formation are molecularly orchestrated, and how GC reaction is balanced by follicular helper T (Tfh) cells and follicular regulatory T (Tfr) cells. In our previous studies, we have delineated molecular pathways that control Tfh cell development and positioning, unveiled positive feedback loops that promote affinity maturation of GC B cells, and identified the G-protein couple receptor that contributes to sexual dimorphism in humoral immunity.