Scenario for lymphoma cell homing and cellular interactions in the lymphoma niche. Fibroblatic reticular cells (FRCs) secrete CCL21 through which CCR7-expressing lymphoma cells are attracted into the lymph node (or spleen) and home to the FRCs in the T-cell region. The lymphoma cells themselves secrete lymphotoxin through which they stimulate lymphotoxin receptor–expressing FRCs. In the niche, lymphoma B cells receive survival signals, presumably including Indian hedgehog secreted by FRCs and CD40 stimulation through CD40 ligand-expressing CD4⁺ T cells. B indicates lymphoma B cell; FRC, fibroblastic reticular cell; HEV, high endothelial venules; Ihh, Indian hedgehog; LT receptor, lymphotoxin receptor; and T, T cell.