Background and Purpose Platelet aggregation plays an important role in
the pathogenesis of thromboembolic cerebrovascular disease. Leukocyte
s can efficiently stimulate as well as inhibit platelet aggregability.
We studied the influence of leukocytes on collagen-induced platelet a
ggregation in patients with acute ischemic stroke. Methods We investig
ated 23 patients within 2 days after stroke and 23 healthy age- and se
x-matched control subjects and determined collagen-induced platelet ag
gregation in platelet-rich plasma with or without addition of polymorp
honuclear or mononuclear leukocytes. Results Platelet aggregation with
out leukocytes tended to be lower in patients than in control subjects
(P=.06). Mononuclear leukocytes reduced (P=.018) and polymorphonuclea
r leukocytes tended to reduce (P=.06) platelet aggregation in patients
. Leukocytes did not significantly alter platelet aggregation in contr
ol subjects. In the presence of either mononuclear or polymorphonuclea
r leukocytes, platelet aggregation was significantly lower in patients
than in control subjects (P=.004 and P=.008). The ratio of polymorpho
nuclear leukocytes to platelets in venous blood was higher in patients
than in control subjects (P<.001). Conclusions Mononuclear-and less c
learly polymorphonuclear-leukocytes possess a platelet aggregation-inh
ibiting potential in the early stages after ischemic stroke, a feature
with possible antithrombotic effects.