CXCL13 and myeloid sarcoma: We studied serum and CSF levels of soluble factors involved in naïve B cell recruitment (CXCL13), in follicular reaction (IL-21) and intrathecal B cell survival (BAFF) in MS patients at clinical onset and correlated their intrathecal synthesis with local Ig production and with magnetic resonance imaging (MRI) parameters of white and gray matter damage.