Influences of the cellular microenvironment on FL cells. Potential interactions between FL cells and local FDCs and TFH cells are indicated. High levels of IL-4 are likely to polarize the tumor-associated macrophages (TAM) to M2 type with upregulated DC-SIGN expression and subsequent engagement of mannosylated surface immunoglobulin on FL cells. BAFF, B-cell–activating factor; BAFFR, BAFF receptor; ICOS, inducible costimulator; ICOSL, ICOS ligand; MHC, major histocompatibility complex; TCR, T-cell receptor.