Summary
Monocytes can play a role in the activation of coagulation via increased procoagulant
activity (PCA). We investigated the level of monocyte PCA in 19 patients with systemic
lupus erythematosus (SLE), given the high rate of thrombotic events in this condition.
Nine of these subjects also presented the lupus anticoagulant (LA). The PCA generated
by patient monocytes was significantly higher than control values and was identified
as tissue factor-like. Moreover, the number of monocytes with membrane-associated
D dimer, a parameter whieh we have shown to be correlated with the PCA expressed in
vitro by endotoxin-activated monocytes, was also significantly increased. Serum from
both groups of patients (i.e. SLE and SLE + LA) stimulated the generation of PCA by
control monocytes. By contrast, purified IgG from both patient groups had the same
effect as control IgG on PCA generation by control monocytes. The nature of the stimulating
agent in the serum was not identified. In conclusion, increased monocyte PCA may account
for the increased incidence of thrombosis in SLE patients, although other, superimposed,
factors would appear to exist in SLE + LA patients, given the higher incidence of
thrombosis in this subgroup.
