Background Thrombosis of arteries in the central nervous system (CNS) represents the most frequent CNS manifestation and the most frequent arterial event in antiphospholipid syndrome (APS). Previous in vivo studies demonstrated that beta2 glycoprotein I (β2GPI) - the main antigenic target for anti-phospholipid antibodies (aPL) - does not localize in brain in resting conditions. However, β2GPI is detectable on the brain vascular endothelium in association with IgG and complement elements in immunized mice treated with lipopolysaccharide. These data suggest that after an appropriate second hit, β2GPI can play a critical role of in APS CNS damage, likely interacting with the complement system. To date, the pathophysiological functions of β2GPI in brain ischemic injury have not been investigated.

Objectives To investigate the presence and the distribution of the activated form of β2GPI in the ischemic brain at different time points.

Methods Eleven-week old male mice underwent focal cerebral ischemia induced by 60' transient middlecerebral artery occlusion (tMCAo), or sham-operation. Mice were sacrified at 90', 6h, 24h, 48h, 4d or 7d after tMCAo to obtain brains and plasma. The presence and time course of β2GPI deposition within the ischemic territory and its spatial distribution relative to blood vessels and brain cells were defined the by post mortem immunofluorescence and confocal microscopy. The activated β2GPI was detected by anti-beta2 glycoprotein I minibody (MBB2) – a human monoclonal IgG antibody targeting β2GPI domain I.

Results β2GPI was present in the ischemic brain tissue starting from 90' after ischemic onset and was still detectable at 7d. β2GPI localized within blood vessels and in brain parenchyma at all times. Notably, at 24h β2GPI was mainly extravascular and colocalized with neurons (NeuN positive cells). Sham-operated mice showed only a faint signal for β2GPI.

Conclusions β2GPI is present in its activated conformation in the brain vessels and tissue after experimental cerebral ischemia. It localizes on neurons in brain ischemic areas. These data suggest that an ischemic/inflammatory hit may up-regulate β2GPI tissue presence and may expose the N-terminal domain I of the molecule which is thougth to be the main target for pathogenic aPL.

Disclosure of Interest None declared