Background Lungs in Rheumatoid arthritis (RA) seem to play an important role, not only as an extra-articular manifestation but also as a site of initiation of the disease and activation for the immune response. B lymphocytes are thought to be involved in the pathophysiology of RA and interstitial lung disease (ILD). The encouraging results of the use of Anti-CD20 treatments to stabilize articular symptoms and lung involvement reinforce this theory. Serum Free immunoglobulin Light Chains (FLC) might represent, in this context, an interesting marker of B lymphocytes activation during this disease.

Objectives To determine the serum FLC levels in RA patients with and without ILD and to study their possible association with disease characteristics and activity.

Methods Fifteen RA patients with clinically symptomatic interstitial lung disease, confirmed by computed tomography (RA-ILD) (53.3% females; mean age 61,27±6,48 years) and age matched RA patients (66.7% females) with no clinically evident interstitial disease (non-ILD) were studied. Clinical and immunological inflammatory characteristics were assessed for all the patients. FLC levels were quantified by turbidimetry (Freelite TM Kappa and Lambda Kits, The Binding Site, UK).

Results The mean serum FLC-κ levels (RA-ILD: 40,74±16,94 ng/ml vs non-ILD 24,88±8,87 ng/ml, p=0,003) and FLC-λ levels (RA-ILD: 37,34±16,56 ng/ml vs non-ILD 26,28±7,22 ng/ml, p=0,028) were significantly higher in patients with ILD compared to non-ILD, while the serum FLC-ratioκ/λ (RA-ILD: 1,15±0,38 vs non-ILD 1,00±0,43, p=0,304) were comparable.

There was no significant difference for the DAS28 disease activity score between both groups (RA-ILD: 4,6±1,5 vs non-ILD 4,38±1,46, p=0,69). No significant correlations were found between the DAS28-score and FLCκ, FLCλ and FLC-ratioκ/λ (p>0,05). FLC-κ levels correlated significantly with ESR and CRP levels (p<0.001), FLC-λ levels with CRP (p=0,005) but not with ESR (p=0,247) and FLC-ratioκ/λ did not correlate with both ESR and CRP levels.

Conclusions High levels of serum FLC are associated with RA-ILD and with a higher degree of inflammation, supporting the role of B cell activation in the pathophysiology of RA with ILD.

Disclosure of Interest None declared