Induction of Auto-Antibodies Against β(2) -Glycoprotein I in Mice by Protein H of Streptococcus Pyogenes.

Background: The antiphospholipid syndrome (APS) is characterized by the persistent presence of auto-antibodies against β(2) -Glycoprotein I (β(2) -GPI). β(2) -GPI can exist in two conformations. In plasma it is a circular protein, whereas it adopts a fish-hook shape after binding to phospholipids. Only the latter conformation is recognized by patient antibodies. β(2) -GPI has been shown to interact with Streptococcus pyogenes. Objective: Here we evaluated the potential of S. pyogenes derived proteins to induce auto-antibodies against β(2) -GPI. Methods and results: Four S. pyogenes surface proteins (M1 protein, protein H, SclA and SclB) were found to interact with β(2) -GPI. Only binding to protein H induces a conformational change in β(2) -GPI, thereby exposing a cryptic epitope for APS-related auto-antibodies. Mice were injected with the four proteins. Only mice injected with protein H developed antibodies against the patient antibody related epitope in domain I of β(2) -GPI. Patients with pharyngotonsillitis caused by S. pyogenes who developed antibodies towards protein H also generated anti-β(2) -GPI antibodies. Conclusion: Our study demonstrated that a bacterial protein can induce a conformational change in β(2) -GPI resulting in the formation of auto-antibodies against β(2) -GPI. This constitutes a novel mechanism for the formation of auto-antibodies against β(2) -GPI.