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Antiphospholipid antibodies: new perspectives on antigenic specificity
1Department of Medicine, Dalhousie University, Halifax, Canada.
The Journal of Rheumatology
|November 1, 1992
Summary
Antiphospholipid antibodies (aPL) in systemic lupus erythematosus (SLE) patients require a cofactor for binding to cardiolipin. Beta 2 glycoprotein I (β2GPI) acts as this crucial cofactor, but is not antigenic alone.
Area of Science:
- Immunology
- Rheumatology
- Clinical Chemistry
Background:
- Antiphospholipid antibodies (aPL) are prevalent in Systemic Lupus Erythematosus (SLE) and Antiphospholipid Antibody Syndrome (APS).
- These antibodies are associated with disease complications, highlighting the need to understand their binding mechanisms.
Purpose of the Study:
- To investigate the cofactor requirement for IgG binding to cardiolipin in SLE and APS patients.
- To identify the specific cofactor involved in aPL-mediated pathogenicity.
Main Methods:
- Purification of IgG from patients with high aPL levels.
- Modified ELISA assays excluding cofactors, followed by addition of fetal calf serum, normal human serum (NHS), and purified beta 2 glycoprotein I (β2GPI).
Main Results:
- Patient IgG strongly bound cardiolipin only in the presence of a cofactor found in serum and lipoprotein fractions.
- Purified β2GPI effectively substituted for serum cofactor in 9 out of 11 patient samples.
- Coating ELISA plates with β2GPI alone showed minimal reactivity with patient sera or IgG.
Conclusions:
- A cofactor is essential for cardiolipin binding by aPL in most SLE/APS patients.
- Beta 2 glycoprotein I (β2GPI) functions as the primary cofactor in this interaction.
- Neither cardiolipin nor β2GPI appears to be directly antigenic in this assay system, suggesting a complex antigen-antibody interaction.