Anti beta 2 Glycoprotein 1 IgM

The antiphospholipid syndrome (APS) is a disorder that
presents peculiar symptoms: arterial and venous
thrombosis, thrombocytopenia, ulcers of the lower limbs,
hemolytic anemia, loss of the fetus during pregnancy and
is associated with the presence of antiphospholipid
antibodies. Antiphospholipid antibodies represent a large
and heterogeneous immunoglobulins group, including
anticardiolipin antibodies and lupus anticoagulant. The
former are diagnosed by on their reactivity with cardiolipin
or other anionic phospholipids in ELISA test, while the
latter is detected in phospholipid-dependent coagulation
tests (aPTT, KCT, dRVVT). In early '90s it was observed
that antiphospholipid antibodies are not directed against
anionic phospholipids, as long it was considered, but they
react with plasma proteins bound to anionic
(phospholipidic) surfaces. In fact about cardiolipin, it was
observed the need of a cofactor for antibodies binding, this
cofactor was identified in β2 glycoprotein 1 (β2-GP1). The
β2 glycoprotein 1 is a plasma glycoprotein of molecular
weight of 50 kD, which is complexed to lipoproteins for
40%. A patient with clinical suspicion of APS, who has an
high titre of anti-beta2GP1 antibodies, even if LAC or anti- cardiolipin antibodies are negative, has a strong chance of
having the antiphospholipid syndrome, because these
antibodies recognize β2-GP1 bound to the surface of
phospholipid (cardiolipin). These proteins seem to express
their antigenicity only after contact with specific areas such
as the anionic phospholipid surface or very hydrophilic
plastic surfaces.
The importance of ELISA anti-phospholipids test, including
the anti-β2-GP1 test, lies in the fact that a positive test if
associated with one or more of the symptoms can confirm
a diagnosis of APS.