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SAEDIS SAEVARSDOTTIR, KRISTJAN STEINSSON, GERDUR GRONDAL, and HELGI VALDIMARSSON

ABSTRACT.

Objective. Mannan-binding lectin (MBL) is present in serum and synovial fluid; its levels vary widely, and the variations are strongly associated with polymorphisms in the MBL2 gene. Studies have compared MBL in patients with rheumatoid arthritis (RA) and in unrelated controls, but the findings have been contradictory. In the first family-based study, we compared MBL levels in patients with RA to population controls and also to their nonaffected first-degree relatives, who may be regarded as optimal controls because of less genetic variation.

Methods. Serum levels of MBL and rheumatoid factor were analyzed in 210 patients with RA and 406 of their first-degree relatives from 74 extended families. Population controls for MBL levels were 330 randomly selected adult Icelanders.

Results. Patients with RA had higher MBL levels in serum (median 1553 µg/l) than their first-degree relatives (1073 µg/l; p = 0.003) and the unrelated controls (938 µg/l; p < 0.0001). No association was found between MBL and rheumatoid factor.

Conclusion. Patients with RA had markedly higher MBL levels than their close relatives and controls, indicating that high MBL may predispose to RA. As MBL has been shown to bind potential arthritogenic agents including modified immunoglobulins, cellular debris, and microorganisms, our findings suggest that high MBL could trigger complement mediated inflammation within joints. (First Release June 15 2007; J Rheumatol 2007;34:1692-4)

Key Indexing Terms:

MANNAN-BINDING LECTIN
RHEUMATOID ARTHRITIS
RHEUMATOID FACTOR
EXTENDED FAMILY
COMPLEMENT

From the Department of Immunology and Center for Rheumatology Research, Landspitali University Hospital, Reykjavik, Iceland.

Supported by the Icelandic Research Fund for Graduate Students and the Science Fund of Landspitali University Hospital.

S. Saevarsdottir, MD, PhD, Rheumatology Trainee, Rheumatology Unit, Karolinska University Hospital, Stockholm, Sweden; K. Steinsson, MD, PhD, Clinical Professor, Chief, Center for Rheumatology Research and Department of Rheumatology; G. Grondal, MD, PhD, Clinical Associate Professor, Rheumatologist; H. Valdimarsson, MD, FRCPath, Professor Emeritus, Department of Immunology, Landspitali University Hospital.

Address reprint requests to Dr. S. Saevarsdottir, Rheumatology Unit, Department of Medicine, Karolinska University Hospital, 17176 Solna, Stockholm, Sweden. E-mail: saedis.saevarsdottir@karolinska.se

Accepted for publication April 28, 2007.