BAFF is decreased in the cerebrospinal fluid of multiple sclerosis at clinical onset

B-cells are thought to play a relevant role in multiple sclerosis (MS) pathology. BAFF (B cell activating factor of the TNF family) is a B-cell survival factor constitutively produced inside the CNS by astrocytes. We studied the intrathecal synthesis of BAFF in MS at clinical onset. Paired serum and cerebrospinal fluid (CSF) specimens from 40 clinically isolated syndromes (CIS) suggestive of MS or early relapse-onset MS (eRRMS) and from 18 healthy controls (HC) were analysed. Patients were classified based on the detection of oligoclonal IgG bands in the CSF (IgGOB+ and IgGOB-). BAFF was detected by highly sensitive ELISA and its ratio (CSF-BAFF/serum-BAFF, QBAFF) and Index (QBAFF/QAlb, BAFF-Index) were calculated. IgGOB+ presented lower CSF concentrations of BAFF compared to both HC and IgGOB- (p<0.05). BAFF Index was significantly lower in IgGOB+ compared to both HC and IgGOB- (p<0.01). A significant inverse correlation between QIgG and QBAFF (r: -0.4, p<0.05) and between BAFF index and IgGIF (r: -0.4, p<0.05) or IgG Index (r: -0.4, p=0.05) was found in IgGOB+. The decreased CSF levels of BAFF in IgGOB+ at clinical onset suggest the absorption of this factor by intrathecally recruited B cells since the early disease phases.