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Kinetic analysis of immune complex solubilization: complement function in relation to disease activity in SLE
G Sturfelt1, O Nived, A G Sjöholm
1Department of Rheumatology, University Hospital, Lund, Sweden.
Insights
Impaired immune complex solubilization and complement function are linked to severe systemic lupus erythematosus (SLE) disease activity. These assays may help monitor SLE progression and treatment effectiveness.
Area of Science:
- Immunology
- Rheumatology
- Clinical Chemistry
Background:
- Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by immune complex deposition.
- Complement system activation is implicated in SLE pathogenesis, but its precise role in disease activity and monitoring remains under investigation.
Purpose of the Study:
- To investigate immune complex solubilization and complement function in relation to disease activity in SLE patients.
- To assess the utility of these assays for monitoring SLE disease progression.
Main Methods:
- Serial investigation of immune complex solubilization, haemolytic complement function, and complement proteins in 25 SLE patients.
- Clinical assessment of disease activity using the SLEDAI (Systemic Lupus Erythematosus Disease Activity Index).
- Kinetic analysis of complement pathways (classical and alternative) and C1 inhibitor complexes.
Main Results:
- Decreased immune complex solubilization capacity strongly correlated with severe SLE disease activity.
- Impaired classical pathway function was persistent in most patients, while impaired alternative pathway function was associated with severe active disease.
- Early detection of impaired complement function preceded clinical manifestations in some patients, suggesting potential for predictive monitoring.
Conclusions:
- Impaired complement function, particularly the alternative pathway, is crucial in severe SLE.
- Immune complex solubilization and complement function assays are valuable tools for monitoring SLE disease activity and guiding therapeutic interventions.
Abstract:
Solubilization of preformed bovine serum albumin (BSA) rabbit anti-BSA complexes in serum with kinetic analysis, haemolytic complement function, complement proteins C1q, C4, C3 and complexes containing C1 inhibitor (C1 INH-C1r-C1s-C1 INH) were serially investigated in relation to disease activity in 25 patients with systemic lupus erythematosus (SLE). Clinical assessment of disease activity was expressed using a validated global index (SLEDAI). Markedly decreased capacity to solubilize immune complexes in serum was mainly found in sever disease. By serial analysis, evidence of fairly persistently impaired classical pathway function was found in most of the patients. In partial contrast, impaired alternative pathway function was more clearly associated with active severe disease. Immune complex solubilization during short incubation (5-10 minutes) correlated with classical and alternative pathway-mediated haemolysis. Solubilization during long incubation (40 minutes) was correlated with haemolytic alternative pathway function. In some patients gradual impairment of solubilization during short incubation, and reduced classical pathway haemolytic activity were detectable 2-4 months before clinical manifestations prompted therapeutical intervention. SLEDAI was negatively correlated with solubilization during prolonged incubation (40 minutes) and with haemolytic alternative pathway function, further emphasizing involvement of the alternative pathway in severe disease. The findings emphasize the importance of impaired complement function due to complement activation in SLE. Assays for immune complex solubilization or other complement functions appear to be useful for monitoring disease activity in SLE.