CXCL13 expression in CNS lymphomas. Expression of CXCL13 in a diagnostic specimen of de novo PCNSL (A) and in relapsed SCNSL (B), as demonstrated by immunohistochemistry (×1000). CXCL13 expression is most evident in stromal elements including tumor blood vessels. (C) Quantitative RT-PCR demonstrates markedly increased expression of CXCL13 in diagnostic specimens of PCNSL (N = 23). CXCL13 transcript levels were similar in PCNSL compared with reactive pharyngeal tonsils (N = 2) and nodal DLBCL (N = 9) but barely detectable in specimens of normal brain (N = 3 cases). (D) CXCL13 protein is markedly increased in CSF in association with both PCNSL and SCNSL compared with the vast majority of neuro-inflammatory conditions and other brain tumors. The highest CSF concentration of CXCL13 was detected in association with relapsed CNS non-Hodgkin lymphoma.