Induction of neovascularization by activated human monocytes

Neovascularization, the process of new blood vessel growth, is an important feature of many pathologic and physiologic processes. Monocytes were isolated from citrated blood buffy coat of healthy adult human donors on Ficoll-Hypaque gradients. Mononuclear cells from these gradients were fractionated on discontinuous Percoll gradients; monocyte-enriched fractions were isolated and assessed for angiogenic activity in rat corneas. Freshly isolated monocytes as well as monocytes cultured for 20 hr on fibronectin-coated collagen gels failed to stimulate neovascularization. In contrast, adherent monocytes activated with concanavalin A (25 μg/ml) or endotoxin (5 μg/ml) for 20 hr were found to be potently angiogenic. We conclude that peripheral blood monocytes must be activated to acquire the ability to induce new blood vessel growth, a process central to inflammation, would healing, and tumor development.