Summary
The presence of lupus anticoagulant (LAC) is strongly correlated with a history of
thrombosis in patients with SLE. LAC activity can be caused by anti-prothrombin (FII)-
and/or anti-β2glycoprotein I (β2GPI)-antibodies.
In the present study, the contribution of anti-FII-antibodies to LAC activity was
measured in 28 LAC positive plasmas. Plasmas were incubated with prothrombin or BSA,
immobilized on CNBr-activated Sepharose, to absorb all anti-FII-antibodies. In 4 out
of the 28 plasmas LAC activity was completely dependent on anti-FII-antibodies. In
7 out of the 28 plasmas, anti-FII-antibodies did not contribute to LAC activity. These
anti-FII-antibodies can be regarded as non-functional antibodies. In the majority
(17/28) of the samples, LAC activity within a single plasma was caused by a combination
of antibodies with different specificities. Both dRVVT and KCT showed comparable sensitivity
for the detection of functional anti-FII-antibodies.
In conclusion, in most samples LAC activity is not caused by anti-FII-antibodies alone
but by a combination of different types of antibodies. The presence of LAC activity
and anti-FII-antibodies in one plasma does not automatically implicate that these
antibodies are responsible for the LAC activity.