The chemokine CXCL13, also known as BCA-1 (B-cell-attracting chemokine-1) or BLC (B-lymphocyte chemoattractant), which belongs to the CXC chemokine family. CXCL13 and its receptor CXCR5 control the organization of B cells within follicles of lymphoid tissues. CXCL13 is known to dictate homing and motility of B cells in lymphoid tissue and has been implicated in the formation of ectopic lymphoid tissue in chronic inflammation. It involves in B-cell compartmental homing within secondary lymphoid organs and recently implicated in the pathogenesis of inflammatory and malignant lymphocyte-mediated diseases. In Primary central nervous system lymphoma (PCNSL), expression of BCA-1 by malignant lymphocytes and vascular endothelium may influence tumor development and localization to central nervous system (CNS). In T-lymphocytes, CXCL13 expression is thought to reflect a germinal center origin of the T-cell. CXCL13 expression may also provide an additional useful tool for the diagnosis of Angioimmunoblastic T-cell lymphoma (AITL).