The role of EZH2 in germinal center biology and postulated role in lymphomagenesis. EZH2 is a histone methyltransferase and increases its activity when B cells enter the germinal center in response to antigen. The upregulated EZH2 prevents the cells from exiting the germinal center until the appropriate germinal center immune response has occurred. When the B cells are ready to differentiate into plasma cells and memory B cells, EZH2 downregulates permitting B cell exit. About 20 percent of follicular lymphomas have a gain of function mutation in EZH2, creating a permanent “locked in” state and presumably contributing to lymphoma development and proliferation.