Erythrocyte CR1 (C3b/C4b receptor) levels and disease activity in patients with SLE
B S Thomsen1, H Nielsen, V Andersen
1Laboratory of Medical Immunology, Rigshospitalet, Copenhagen, Denmark.
Insights
Patients with systemic lupus erythematosus (SLE) exhibit significantly lower erythrocyte complement receptor 1 (CR1) levels. These low CR1 levels correlate with increased disease activity and immune complex formation.
Area of Science:
- Immunology
- Rheumatology
Background:
- Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune complex deposition.
- Complement receptor 1 (CR1) plays a crucial role in immune complex clearance.
Purpose of the Study:
- To investigate the levels of CR1 on erythrocytes in SLE patients.
- To assess the correlation between CR1 levels, circulating immune complexes (IC), and disease activity in SLE.
Main Methods:
- Enzyme-linked immunosorbent assay (ELISA) for CR1 levels on erythrocytes.
- Polyethylene glycol precipitation method for circulating immune complexes (IC).
- Intermediate gel rocket immunoelectrophoresis for C3d split products.
Main Results:
- SLE patients showed significantly lower mean erythrocyte CR1 levels compared to controls (40% vs. 70%, p < 0.001).
- Elevated circulating IC were found in 38% of samples, and elevated C3d in 72%.
- Low CR1 levels negatively correlated with disease activity, IC levels, and C3d concentrations.
Conclusions:
- Reduced erythrocyte CR1 expression is a feature of SLE.
- Lower CR1 levels are associated with increased immune complex burden and disease activity in SLE.
- CR1 levels demonstrate relative stability despite fluctuations in disease activity.
Abstract:
Fifty-four patients with systemic lupus erythematosus (SLE) were examined for (1) CR1 (C3b/C4b receptor) levels on erythrocytes by an enzyme-linked immunosorbent assay, (2) levels of circulating immune complexes (IC) by a polyethylene glycol precipitation complement consumption method, and (3) concentrations of C3d split products in plasma by intermediate gel rocket immunoelectrophoresis. A preponderance of low CR1 levels was found among patients with SLE (mean 40%, range 13-106) as compared with normal controls (mean 70%, range 24-130) (p less than 0.001). The concentrations of circulating IC were elevated in 38% of 58 samples. The concentrations of C3d were elevated in 72%, and were positively correlated with the levels of IC (tau = 0.28; p less than 0.005) and with disease activity as assessed by a modification of the UCH/Middlesex criteria. Negative correlations were seen between the CR1 numbers and disease activity (p = 0.01), concentrations of circulating IC (tau = -0.14; p less than 0.005), and C3d (tau = -0.21; p less than 0.005). The changes found in CR1 levels on repeated study were, however, relatively small (less than or equal to 27%; median 5), even during periods of changing disease activity.
