Generation of biologically active angiostatin kringle 1-3 by activated human neutrophils.

The contribution of polymorphonuclear neutrophils (PMN) to host defense and natural immunity extends well beyond their traditional role as professonial phagocytes. In this study, we demonstrate that, upon stimulation with proinflammatory stimuli, human PMN release enzymatic activities that, in vitro, generate bioactive angiostatin fragments from purified plasminogen. We also provide evidence that these angiostatin-like fragments, comprising kringle domain 1 to kringle domain 3 (kringle 1-3) of plasminogen, are generated as a byproduct of the selective proteolytic activity of neutrophil-secreted elastase. Remarkably, affinity purified angiostatin kringle 1-3 fragments generated by neutrophils inhibited basic fibroblast growth factor (FGF2) plus vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation in vitro, and both VEGF-induced angiogenesis in the matrigel plug assay and FGF2-induced angiogenesis in the chick embryo chorioallantoic membrane assay, in vivo. These results represent the first demonstration that biologically active angiostatin-like fragments can be generated by inflammatory human neutrophils. Since angiostatin is a potent inhibitor of angiogenesis, tumor growth and metastasis, the data suggest that activated PMN not only act as potent effectors of inflammation, but might also play a critical role in the inhibition of angiogenesis in inflammatory diseases and tumors, by generation of a potent anti-angiogenic molecule.