CXCL-13 serum levels in patients with rheumatoid arthritis treated with abatacept

Objectives: C-X-C motif chemokine 13 (CXCL-13), which is expressed by synovial follicular dendritic cells and activated mature antigen-experienced T-helper cells, has been described as a surrogate marker of lymphoid phenotype of synovitis in rheumatoid arthritis (RA). A preferential response to anti-interleukin-6 receptor (IL-6R) as compared to anti-tumour necrosis factor alpha (TNFα) monotherapy has been described in patients with increased levels of CXCL-13. We hypothesised that serum levels of CXCL-13 could be used as a biomarker of response to treatment with abatacept (ABA), a T-cell co-stimulation blocker. Methods: Serum levels of CXCL-13 and of soluble intracellular adhesion molecule 1 (sICAM-1) (a putative marker of the myeloid subtype of synovitis) were measured by indirect solid-phase enzyme immunoassays, before (T0) and after 6 months of therapy with ABA (T6) in 63 patients with RA. Circulating T follicular helper cells and B cell subpopulations were identified by flow-cytometry. Results: At T0, CXCL-13 serum levels were higher in RA patients than in healthy controls (p=0.0001) and correlated with disease activity, while no difference between the two groups was observed as far as sICAM-1 levels. Serum levels of CXCL-13 levels decreased after therapy with ABA both in patients who achieved a clinical response (p<0.01) and in non-responders (p=0.01), whereas sICAM-1 levels did not significantly change. When comparing RA patients who responded to ABA with non-responders no significant difference of baseline serum levels of CXCL-13 was observed. Conclusions: CXCL-13 serum levels are raised in RA patients and decrease after therapy with ABA. We were not able to demonstrate that serum CXCL-13 levels predict the clinical response to ABA in RA patients.