Summary
The effect on platelet function of plasma from 9 patients with primary antiphospholipid
syndrome (PAS) with previous thrombotic episodes was investigated under flow conditions.
Five asymptomatic individuals with antiphospholipid antibodies (aPL) (A-aPL) and 14
normal controls were also studied. Patients and controls plasmas were added (1:20
v/v) to anticoagulated blood and perfused through annular chambers containing collagen
rich vessel segments. The interaction of platelets with vessel subendothelium was
morphometrically evaluated in thin sections. An increase in both covered surface and
thrombi formation was observed in perfusions in the presence of PAS-plasma (mean ±
SD: 34.2% ± 9.6% and 23.2% ± 10.0% respectively) compared with control plasmas (21.4%
± 7.3% and 10.1% ± 7.7%, p<0.01). Affinity purified anticardiolipin antibodies from
one PAS patient showed a similar effect when added to normal blood. In contrast, A-aPL
plasma had no effect on platelet-subendothelium interaction. In parallel studies,
the same plasmas were incubated with isolated normal platelets before and after activation
with ADP or collagen and the binding of immunoglobulins (Ig) was determined by flow
cytometry. A significantly increased binding of Ig was observed in 8 out of 9 plasmas
from PAS patients when platelets had been activated with collagen but not when resting
or ADP activated platelets were used. No increased Ig binding to platelets was seen
using A-aPL individuals plasma. These observations might help to explain the pathophysiology
of the thrombotic events occurring in patients with PAS.
