FRI0335 Serum Levels of Immunoglobulins and Free Light Chains in Patients with Rheumatoid Arthritis Treated with Abatacept

Background Through costimulation blockade, Abatacept (ABA) may down-modulate the immune responses of B lymphocytes in Rheumatoid Arthritis (RA). We previously showed that ABA reduces the serum levels of different classes of anti-cyclic citrullinated peptide (anti-CCP), and rheumatoid factor (RF), and limits the differentiation of B lymphocytes into post-switch memory cells (1). Free light chains (FLC) are produced by B cells, plasmablasts and plasmacells and raised levels correlate with disease activity in RA. Objectives To evaluate the effect of the ABA on serum levels of immunoglobulins (Ig) and FLC. To evaluate the baseline levels of these parameters as predictors of response to ABA. Methods 30 RA patients (pts) (26 female; median-age: 53 years [IQR: 44-60] treated for at least 6 months with ABA and 24 healthy controls (HC; 18 female; age: 39 [34-46]) were evaluated. Serum Ig levels were measured by a nephelometric-immunoassay (Siemens Healthcare Diagnostics Products GmbH). Reference ranges were derived by a consensus group based on the standardization against the calibrated reference material CRM 470. Serum FLC levels were measured by a latex-enhanced immunoassay (The Binding Site, Birmingham, UK). Reference ranges include 100% of a population of 282 HC. Clinical disease activity was evaluated with the DAS28 (based on CRP). Results At baseline (T0), RA pts had higher serum levels of IgM (p Conclusions ABA therapy induced a trend toward normalization of serum levels of total Ig of different classes and of FLC. FLC reduction was significant in pts achieving clinical remission after ABA therapy, but not in those who did not. In our evaluation, the decrease of serum free λ chains was correlated with clinical improvement, and their baseline levels appeared to be associated with clinical response to ABA. References Scarsi M et al; Ann Rheum Dis 2013;72(Suppl3):623 Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.5465