Calprotectin in patients with systemic lupus erythematosus: relation to clinical and laboratory parameters of disease activity.

Calprotectin (L1) is a granulocyte and monocyte cytosolic protein released during activation of these cells. The plasma level of L1 has been shown to be a good marker of disease activity in rheumatoid arthritis. In this cross-sectional study of 100 patients with systemic lupus erythematosus (SLE), the serum level of L1 was found to be higher in patients than in matched controls (3661 micrograms/l versus 1051 micrograms/l; P < 0.001). The serum level of L1 was the only laboratory parameter with significant association to the disease activity index SLEDAI (r = 0.28; P < 0.01). Furthermore, the serum level of L1 was significantly higher in SLE patients with anti-DNA antibodies compared to patients without anti-DNA antibodies (4501 micrograms/l versus 3279 micrograms/l; P = 0.01). SLE patients with arthritis had higher serum levels of L1 than patients without arthritis (7652 micrograms/l versus 2811 micrograms/l; P < 0.01), indicating that the serum level of L1 also reflects arthritis activity in SLE.