Detection and characterization of B cell epitopes on β2-glycoprotein I

Autoantibodies in antiphospholipid syndrome react predominantly with the plasma protein β2-glycoprotein I (β2GPI). Work by a large number of investigators has led to considerable progress in detecting and understanding β2GPI reactivity with autoantibodies. Characterization of B cell epitopes on β2GPI has benefited from an appreciation of its interactions with anionic phospholipids and a variety of microplate surfaces. In particular, autoantibodies to β2GPI are of sufficiently low affinity to require high concentrations of antigen for detectable reactivity. Moreover, some microplate surfaces do not support the proper orientation of β2GPI to allow display of epitopes in a manner accessible to autoantibodies. These concepts have helped to explain previous notions that exposure of cryptic β2GPI epitopes may require interactions with anionic surfaces. Finally, we review evidence identifying a dominant B cell epitope that is partially defined by residues Gly40 and Arg43 on the amino terminal domain of β2GPI.