Anti-B2-Glycoprotein I Antibodies

β₂-Glycoprotein I (β2GPI) is a 50 kDa plasma glycoprotein that binds as a cofactor to anionic phospholipids such as cardiolipin. It also interacts with the membranes of activated platelets and endothelial cells, which play a role in the pathogenesis of antiphospholipid syndrome (APS). During pregnancy, β₂GPI can bind to trophoblast cells. The subsequent binding of anti-β2GPI antibodies may decrease hCG secretion from these cells, potentially leading to defective placentation. β₂GPI also functions as a natural anticoagulant; therefore, the presence of anti-β₂GPI antibodies may increase the risk of thrombosis.

The anti-β2GPI antibody assay is used in conjunction with antiphospholipid antibody testing to aid in the diagnosis of the antiphospholipid syndrome. The three antibody isotypes (IgG, IgM, and IgA) are measured in human serum using an Enzyme-Linked Immunosorbent Assay (ELISA). Purified β₂GPI antigen is bound to the wells of a polystyrene microplate under conditions that preserve the antigen’s native state. Pre-diluted controls and diluted patient sera are added to separate wells, allowing any β₂GPI-specific antibodies to bind to the immobilized antigen. Unbound material is washed away, and an enzyme-labeled anti-human IgG conjugate is added. After incubation, the conjugate binds to any patient antibodies attached to the wells. Following a second wash, a chromogenic substrate is added. The enzyme reaction produces a color change proportional to the amount of antibody present. Absorbance is measured spectrophotometrically and compared with a five-point calibration curve to determine qualitative or semi-quantitative results.

• Room temperature: up to 8 hours
• 2-8°C: up to 48 hours
• -20°C or below: for longer storage

Send frozen serum on dry ice. Do not freeze samples in self-defrosting freeze

Enzyme-Linked Immunosorbent Assay (ELISA)

Negative
Results are reported as negative or positive.

• H. Bas de Laat et al. Clin Immunol. 112:161-168; 2004.
• Di Simone et al. Ann Rheum Dis. 64:462-467; 2005.

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