BSG and B-cell chronic lymphocytic leukemia: Exogenous CyPA (eCyPA) secreted by bone marrow endothelial cells promotes proliferation and homing of MM cells by binding to the receptor CD147 [27].In addition to MM cells, eCyPA also promotes the migration of chronic lymphocytic leukemia (CLL) and lymphoplasmacytic lymphoma (LPL) cells, both of which express CD147 and tend to colonize the bone marrow.This suggests that PPIE, a member of the same family as PPIA, may play an important role in cellular signaling pathways.