Summary
Lupus anticoagulants (LAs) are antibodies which interfere with phospholipid-dependent
procoagulant reactions. Their clinical importance is due to their apparent association
with an increased risk of thrombo-embolic disease. To date there have been few assays
for quantifying the specific activity of these antibodies in vitro and this has hampered
attempts to purify and characterize these antibodies. Methods for determining phospholipid-dependent
generation of thrombin and factor Xa are described. Isolated IgG fractions from 7
of 9 patients with LAs were found to reproducibly inhibit enzyme generation in these
assay systems, permitting quantitative expression of inhibitor activity. Different
patterns of inhibitory activity, based on the relative inhibition of thrombin and
factor Xa generation, were found, further substantiating the known heterogeneity of
these antibodies. These systems may prove helpful in further purification and characterization
of LAs.
