Chemokine CXCL13, the ligand of CXCR5, is overexpressed in areas of actively demyelinating lesions, and almost all B-cells infiltrates in the CNS demonstrate high CXCR5 expression (12, 16), suggesting that CXCR5–CXCL13 axis is the main driver of B-cell recruitment to areas of MS lesions. The gene discussed is CXCL13; the disease is myeloid sarcoma.