Autoimmune antibody positivity Anti-beta 2 glycoprotein I antibody positivity 2019-02-24T13:47:12Z Anti-B2GPI positivity Presence of antibodies against beta 2 glycoprotein I in the circulation. Beta-2 glycoprotein I (beta2GPI) is the principal target of autoantibodies in the antiphospholipid syndrome (APS). Beta2GPI was identified as a primary target of autoantibodies in patients with APS. Beta2GPI is a single-chain protein containing five repeating sequences or domains. Domain V is essential for binding to anionic phospholipid membranes, whereas domain I sticks out into the extracellular space where interactions with other proteins/antibodies can take place 1.