CXCL13 and myeloid sarcoma: BSCB damage is one of the main reasons for inflammatory factors and immune cells entering the CNS to induce neuroinflammation.[4] Clinical trials demonstrated that natalizumab, a monoclonal antibody that prevented the infiltration of immune cells into the CNS, reduced the frequency of onset and delayed the progression of MS.[15] In order to reveal the mechanism of BSCB damage in MS, this study screened the disease progression‐related cytokine CXCL13 by protein mass spectrometry analysis of peripheral blood serum from clinical MS patients and EAE mice.