CXCL13 and primary central nervous system lymphoma: A plethora of functional evidence has demonstrated that CXCL13 and/or CXCR5 participate in the pathogenesis of lymphoma, including mantle cell lymphoma (MCL) [155], follicular lymphoma (FL) [156], diffuse large B-cell lymphoma (DLBCL) [156], primary intraocular lymphoma (PIOL) [157], primary central nervous system lymphoma (PCNSL) [158,159,160], extranodal natural killer (NK)/T-cell lymphoma (ENKTL) [161], and angioimmunoblastic T-cell lymphoma (AITL) [162,163].