Open Access Research article

Increased plasma levels of the soluble Mer tyrosine kinase receptor in systemic lupus erythematosus relate to disease activity and nephritis

Jun Wu14, Carl Ekman1, Andreas Jönsen2, Gunnar Sturfelt2, Anders A Bengtsson2, Anders Gottsäter3, Bengt Lindblad3, Elisabet Lindqvist2, Tore Saxne2 and Björn Dahlbäck1*

Author Affiliations

1 Department of Laboratory Medicine, Section of Clinical Chemistry, Lund University, Wallenberg Laboratory, Skåne University Hospital, Södra Förstadsgatan 101, Malmö, SE 205 02, Sweden

2 Department of Clinical Sciences, Section of Rheumatology, Lund University, Skåne University Hospital, Getingevägen 4, Lund, SE 22185, Sweden

3 Department of Clinical Sciences, Vascular Center, Lund University, Skåne University Hospital, Södra Förstadsgatan 101, Malmö, SE 205 02, Sweden

4 Department of Laboratory Medicine, People's Hospital, Peking University, No.11 Xizhimen South Street, Beijing, 100044, PR China

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Arthritis Research & Therapy 2011, 13:R62  doi:10.1186/ar3316

Published: 15 April 2011

Abstract

Introduction

Mer and Tyro3 are receptor tyrosine kinases important for the phagocytosis of apoptotic cells. Together with Axl, they constitute the TAM receptor family. These receptors can be shed from the cell membrane and their soluble extracellular regions can be found in plasma. The objective of this study was to elucidate whether the plasma levels of soluble Mer (sMer) and Tyro3 (sTyro3) were increased in systemic lupus erythematosis (SLE), rheumatoid arthritis (RA), or critical limb ischemia (CLI).

Methods

ELISA kits were used to test plasma concentrations in controls and in patients with SLE, RA or CLI.

Results

Increased levels of, in particular, sMer and, to some extent, sTyro3, were found in patients with SLE or RA, but not in patients with CLI. Patients with SLE demonstrated the highest sMer levels and there was a strong correlation to higher SLE disease activity score (SLEDAI). In contrast, in patients with RA, the sMer levels did not correlate with the disease activity score (DAS). In SLE, sMer levels were particularly high in those with lupus nephritis, patients who also had decreased C1q levels and increased titers of anti-DNA antibodies. After therapy, the plasma concentrations of sMer decreased in parallel to the decrease in SLEDAI score.

Conclusions

The plasma concentrations of sMer and sTyro3 were significantly increased in patients with active SLE and RA, suggesting the TAM receptor shedding was affected by these autoimmune diseases. In particular, sMer was increased in SLE, the plasma levels of sMer reflecting disease activity.