Antibodies are proteins that are produced by B cells and plays an important role in eliminating the pathogen and cancer cells. Antigen-activated B cells form a specialized microenvironment called germinal center (GC), together with follicular dendritic cells (FDCs), in secondarily lymphoid tissues. In GCs, B cells differentiate to antibody-secreting plasma cells or memory B cells after improving the affinity of antibody. Now, we focus on the immunological functions of FDCs that play a critical role in the regulation of GC B cells responses. Firstly, we have established mouse FDC line, FL-Y, to develop an in vitro culture system that enables us to reproduce cell-cell interactions in GCs. Using this culture system, we identified the novel mechanisms for clonal selection of high-affinity antibody-producing B cells and molecular mechanisms underlying B cell- FDC interaction in GCs. Furthermore, we found that a novel function of FDCs, except for GC B cell differentiation.