Vasculitis in systemic lupus erythematosus (SLE)--assessment of peripheral blood mononuclear cell activation and the degree of endothelial dysfunction: initial report

Abstract

Background: Inflammatory-immune changes in the vascular endothelium are one of the main factors initiating vessel wall damage. Enhanced expression of endothelial adhesion molecules and their receptors on the surface of circulating leukocytes seems to play an important role in the pathogenesis of vasculitis. Increasing evidence indicates endothelial cell activation/damage in SLE. In patients with SLE complicated by vasculitis, enhanced expression of integrin activation markers on the surface of peripheral blood mononuclear cells (PBMCs) has been reported. It seems relevant to assess the mechanisms of inflammatory response involving PBMCs and endothelial cells at particular stages of SLE microangiopathy.

Aim: The main aim was to assess the surface expressions of the integrin adhesion molecules VLA-4 (CD49d) and LFA-1 (CD11a) on PBMCs as well as the number of circulating endothelial cells (CECs) in patients with SLE and complications related to inflammatory microangiopathy and to determine whether these parameters vary depending on disease activity.

Patients: Twenty-nine women with SLE (mean age: 38.72+/-10.23 years) were divided into subgroup I: those with severe disease activity according to the modified disease activity index SLEDAI, characterized by the presence of inflammatory microangiopathy-related complications such as systemic central nervous system affection and/or vasculitis and/or nephritis (15 women, mean age: 38.33+/-11.02 years), and subgroup II: patients with mild or moderate disease activity according to SLEDAI and without vascular complications (14 women, mean age: 39.14+/-9.72 years).

Methods: Expressions of VLA-4 and LFA-1 on the surface of peripheral blood lymphocytes and monocytes were assessed by flow cytometry using monoclonal antibodies. CECs (a marker of endothelial damage) were isolated from peripheral blood with anti-CD146(S-Endo 1)-coated immunomagnetic Dynabeads. Tests for the lupus anticoagulant, antinuclear antibody, anti-dsDNA, and anticardiolipin antibody were performed in every study subject by ELISA. Erythrocyte sedimentation rate and serum levels of fibrinogen, C-reactive protein, the complement components C3 and C4, urea, creatinine, and uric acid were determined by standard methods. Peripheral blood counts and a general urinalysis were also performed.

Results: The mean CEC count was significantly higher in SLE patients than in the control group (15.29+/-12.10 vs. 3.08+/-1.46 cells/ml, p<0.001). CEC counts was notably elevated in patient subgroup II compared with the control group (9.14+/-5.16 vs. 3.08+/-1.46 cells/ml, p<0.05) and in subgroup I compared with subgroup II (21.03+/-13.96 vs. 9.14+/-5.19 cell/ml, p<0.05). In patients with severe SLE flares, CEC count visibly correlated with disease activity assessed by SLEDAI score (R=0.92, p<0.001). The expressions of VLA-4 and LFA-1 on peripheral blood lymphocytes in both patient subgroups were significantly higher than in the control group (subgroup I vs. controls: 1.70+/-1.56 vs. 0.39+/-0.26%, p<0.05, and 1.97+/-2.60 vs. 0.67+/-0.83%, p<0.05; subgroup II vs. controls: 1.71+/-1.04 vs. 0.39+/-0.26%, p<0.001, and 3.32+/-2.48 vs. 0.67+/-0.83%, p<0.05, for VLA-4 and LFA-1, respectively). There was no significant difference between the two subgroups of patients (1.70+/-1.56 vs. 1.71+/-1.04%, p>0.05, and 1.97+/-2.60 vs. 3.32+/-2.48%, p>0.05, respectively). Similarly, the surface expression of LFA-1 on circulating monocytes in patients in both subgroups was notably enhanced over that of the control group (91.44+/-16.00 vs. 84.95+/-19.86%, p<0.05, and 90.11+/-10.34 vs. 84.95+/-19.86%, p<0.05, in subgroups I and II respectively) and was comparable in both subgroups of patients (91.44+/-16.00 vs. 90.11+/-10.33%, p>0.05). The surface expression of VLA-4 on peripheral blood monocytes was considerably higher in patients with severe disease activity than in the control group and in patients with less active disease (77.10+/-13.56 vs. 64.90+/-19.13%, p<0.05, and 77.10+/-13.56 vs. 63.40+/-20.95%, p<0.05, respectively). However, there was no significant difference between patients with mild or moderate disease activity and the control group (63.40+/-20.95 vs. 64.90+/-19.13%, p>0.05).

Conclusions: 1) The number of CECs increases in the course of SLE and correlates with disease activity, indicating progressive endothelial damage.2) The expressions of VLA-4 and LFA-1 on the surface of peripheral blood lymphocytes as well as that of LFA-1 on circulating monocytes are enhanced in SLE patients regardless of disease activity. 3) The expression of VLA-4 on the surface of circulating monocytes is enhanced only in patients with severe disease activity, characterized by the presence of complications connected with inflammatory microangiopathy, which may indicate that the upregulation of VLA-4 expression in monocytes plays a leading role in the pathogenesis of vasculitis in SLE.