Complement C4 – Biomarker for Systemic Lupus Erythematosus (SLE)
Systemic Lupus Erythematosus (SLE) is an autoimmune disorder associated with a deficiency in complement C4. Complement C4 is one of nine components of the complement system which is an integral part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from the host, promote inflammation, and attack the cell membrane of pathogens.
Complement C4 is a vital component of two immunology pathways: Classical pathway and Mannrose Binding Lectin (MBL) pathway.
The classical pathway is triggered by antibody-antigen complexes which induces a conformational change in the C1 complex. The activated C1 complex cleaves the C4 component, resulting in a reactive C4b which covalently binds to proteins or polysaccharides at the surface in close proximity of the C1 component. The bound C4b complexes binds to the C2 component rendering C2 for proteolysis by C1.
The MBL pathway is activated through the binding of MBL to mannose residues on the pathogen surface. This in turn activates the MBL-associated serine proteases, MASP-1 and MASP-2, which activates the C4 and C2 components, to form the C3 convertase, C4b2a. The C4b2a complex splits C3 into two fragments which causes the release of vasoactive mediators such as histamine.
Complement C4 deficiency is commonly associated with systemic lupus erythematosus (SLE).
According to lupus.org, 16,000 new cases of lupus are reported each year. Approximately 1 in 250 people may end up developing SLE at some point with 90% of SLE patients being female aged between 15-44 years. The causes of SLE are unknown, but are believed to be linked to environmental, genetic, and hormonal factors. 1.5 million Americans are living with diagnosed lupus.
There are four forms of lupus:
- Systemic – accounts for approximately 70% of all lupus cases. In half of these cases, a major organ or tissue in the body, such as the heart, lungs, kidneys, or brain will be affected.
- Cutaneous lupus – accounts for approximately 10% of all lupus cases and only affects the skin.
- Drug-induced lupus accounts for approximately 10% of all lupus cases and is caused by high doses of certain medications.
- Neonatal lupus is a rare condition in which the mother’s antibodies affect the fetus. At birth, the baby may have a skin rash, liver problems, or low blood cell counts, but these symptoms typically disappear completely after six months with no lasting effects.
The Randox Complement C4 assay
The Randox Complement C4 assay is used for the quantitative in vitro determination of complement C4 concentration in serum. The Randox Complement C4 assay can be used as a biomarker in the diagnosis and monitoring of SLE. It is the cell-bound levels of processed complement activation products, especially E-C4d (erythrocyte-bound C4) that makes the complement C4 assay a biomarker for SLE.
Key Features of the Randox Complement C4 assay
Liquid ready-to-use reagents – The Randox reagent comes in a convenient liquid format requiring minimal preparation thus reducing the risk of errors.
Exceptional correlation with standard methods – The Randox methodology was compared against other commercially available methods and the Randox Complement C4 assay showed a correlation coefficient of r=0.98.
Wide measuring range – The healthy range for Complement C4 is 7 -49 mg/dl. The Randox Complement C4 assay can comfortably detect levels outside of the healthy range measuring between 2.90 – 152 mg/dl.