Serum immunoglobulin free light chain assessment in rheumatoid arthritis and primary Sjogren's syndrome.
BACKGROUND
B cell activation may result in an increased secretion of immunoglobulin free light chains (FLCs) in autoimmune diseases.


OBJECTIVE
To analyse serum FLC levels in patients with rheumatoid arthritis and in those with primary Sjögren's syndrome (pSS).


METHODS
Blood samples were collected from 80 healthy blood donors, 50 patients with rheumatoid arthritis and 139 patients with pSS. Serum FLC level was measured using a new quantitative immunoassay.


RESULTS
Mean (standard error (SE)) serum kappa and lambda FLC levels were significantly higher in patients with rheumatoid arthritis and in those with pSS than in controls (kappa : 18.9 (1.1) and 16.3 (1.4) v 10.5 (0.4) mg/l, p<0.001 and p = 0.001, respectively; lambda: 16.7 (1.2) and 19.3 (1.5) v 11.6 (0.6) mg/l, p<0.001 for both). 18 (36%) patients with rheumatoid arthritis and 31 (22.3%) patients with pSS had abnormal serum FLC levels (increased kappa or lambda levels and abnormal ratio of kappa:lambda). Serum kappa and lambda levels were correlated with other B cell activation markers in both diseases. FLC levels increased with disease activity, because, unlike total gammaglobulin and immunoglobulin G levels, they were significantly correlated with Disease Activity Score 28 in patients with rheumatoid arthritis (p = 0.004 for kappa, p = 0.05 for lambda) and with extraglandular involvement in pSS (p = 0.01 for kappa, p = 0.04 for lambda).


CONCLUSIONS
FLC levels are increased and correlate with disease activity in patients with rheumatoid arthritis and in those with pSS, two diseases in which increased risk of lymphoma could result from persistent B cell activation and disease activity. Further studies are required to determine whether FLC assessment could represent a relevant biomarker for response to treatment (especially B cell depletion) and for the risk of lymphoma in autoimmune diseases.
Rhumatologie, Université Paris-Sud 11, INSERM U802, Hôpital Bicêtre, Assistance Publique des Hôpitaux de Paris, Le Kremlin Bicêtre, France.
J-E
JE
Gottenberg
F
F
Aucouturier
J
J
Goetz
C
C
Sordet
I
I
Jahn
M
M
Busson
J-M
JM
Cayuela
J
J
Sibilia
X
X
Mariette
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007074:Immunoglobulin G / Q000097:blood; D007147:Immunoglobulin Light Chains / Q000097:blood*; D007145:Immunoglobulin kappa-Chains / Q000276:immunology; D007146:Immunoglobulin lambda-Chains / Q000276:immunology; D008297:Male; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000097:blood; D012859:Sjogren's Syndrome / Q000276:immunology*; D005719:gamma-Globulins / Q000032:analysis
D007074:Immunoglobulin G; D007147:Immunoglobulin Light Chains; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains; D005719:gamma-Globulins; D012217:Rheumatoid Factor