Abstract
Thrombotic antiphospholipid syndrome (APS) is a condition in which thrombosis in venous,
arterial, and/or small vessels is ascribed to the presence of antiphospholipid antibodies
(aPL). Among the various proposed pathogenic theories to explain thrombotic APS, those
involving the interaction between aPL and the protein C system have gained much consensus.
Indeed, robust data show an acquired activated protein C resistance (APC-R) in these
patients. The role of aPL in this impairment is clear, but the mechanism of action
is uncertain, as the type of aPL and to what extent aPL are involved remains a gray
area. Lupus anticoagulant (LA) is often associated with APC-R, but antibodies generating
LA comprise those directed to β2-glycoprotein I and antiphosphatidylserine/prothrombin.
Moreover, the induction of APC-R by aPL requires the presence of phospholipids and
is suppressed by the presence of an excess of phospholipids. How phospholipids exposed
on the cell membranes work in the system in vivo is unknown. Interestingly, acquired
APC-R due to aPL might explain the clinical phenotypes of thrombotic APS. Indeed,
the literature reports cases of both venous and arterial thromboembolism as well as
skin necrosis, the latter observed in the severe form of protein C deficiency and
in catastrophic APS.
Keywords
protein C - resistance - phospholipid - syndrome - antibodies - thrombosis - lupus
anticoagulant
