Activated human platelets express Fas-L and induce apoptosis in Fas-positive tumor cells.

In addition to their role in hemostasis and thrombosis, platelets are important modulators of immune and inflammatory responses. We provide evidence here that human platelets contain abundant quantities of Fas-L, and upon activation, they express it on their surface as well as release it into medium. This surface-expressed Fas-L is biologically active and can induce apoptosis in Fas-positive human tumor cells. Therefore, activated platelets may represent an important player in Fas/Fas-L-mediated apoptosis.