The antiphospholipid antibody syndrome (APS) is characterized by severe and recurrent thrombotic events, recurrent fetal loss or thrombocytopenia and the repeated detection of antiphospholipid antibodies. This syndrome can be associated with an other autoimmune disease (secondary APS), particularly SLE (141-143) or unreleated to an underlying disease (primary APS). Disease activity in SLE is reported to be accompanied by significantly increased levels of antiphospholipid antibodies (144).
Different groups of autantibodies exist (Table 11).

Tab. 11 Antiphospholipid Syndrome: Different Classes of Antigens

The family of antiphospholipid antibodies binds neutral and negatively charged phospholipids such as cardiolipin, phosphatidyl-serine, phosphatidyl-inositol, phosphatic acid or phosphatidyl-ethanolamine. In the last years it becomes more and more evident that a cofactor, bGP-1 is important for an optimal binding between the phospholipid and its corresponding antibody. Despite intense interest in bGP-1 as a target of the autoimmune response in APS, the physiological role of this normal plasma protein remains obscure. The genetics of bGP-1 have also received considerable interest. Recently, Mehdi et al. (145) described the association of certain b2-glycoprotein I polymorphisms with plasma levels of b2-glycoprotein I. In addition, several groups have reported about an association between bGP-1 polymorphisms and APS (146-148). The clinical relevance of bGP-1 dependent and independent antiphospholipid antibodies is up to now under discussion (149 – 152).