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[Components of the classical complement pathway in systemic lupus erythematosus]
Insights
Genetic deficiencies in complement component 4 (C4) are linked to low levels of CH50, C4, and C2 in systemic lupus erythematosus (SLE) patients. These deficiencies, whether isolated or with complement activation, do not reliably indicate disease activity.
Area of Science:
- Immunology
- Genetics
- Rheumatology
Context:
- Systemic lupus erythematosus (SLE) is an autoimmune disease.
- Complement system components, including C4 and C2, play a role in immune responses.
- Genetic variations in complement genes can influence disease susceptibility and presentation.
Purpose:
- To investigate the relationship between decreased complement component levels (CH50, C4, C2) and genetic factors in SLE patients and their relatives.
- To determine if C4 deficiency is associated with complement activation in SLE.
- To assess the utility of measuring C4 and C2 levels for monitoring SLE disease activity.
Summary:
- Decreased levels of CH50, C4, and C2 in SLE patients and relatives are often associated with genetic deficiencies in the C4 gene loci.
- C4 deficiency can occur in isolation or be linked to complement activation, detectable via C3a des Arg levels in some cases.
- Reduced C4 and C2 concentrations or hemolytic activity in SLE do not serve as reliable indicators of disease activity.
Impact:
- Identifies genetic C4 deficiency as a primary cause for reduced C4 and C2 levels in a subset of SLE patients.
- Highlights the complex interplay between genetic complement deficiencies and complement system activation in SLE.
- Clarifies that C4 and C2 levels are not suitable biomarkers for assessing SLE disease activity, guiding future research and clinical practice.
Abstract:
Measurements of complement components in sera from patients with systemic lupus erythematosus (SLE) and some of their relatives indicated that decreased levels of CH50, C4 and C2 were mostly related to a genetic deficiency at one or both of the loci coding for C4, at least in those patients in whom decreased C4 levels were associated with normal C1 hemolytic activity. C4 deficiency is either isolated or associated with complement activation. In some patients with C4 deficiency, complement activation could only be demonstrated by measuring plasma level of the C3 cleavage fragment, C3a des Arg. Decreased concentration and/or hemolytic activity of C4 and C2 in SLE cannot be used to assess the activity of the disease.