The present invention relates to compositions and methods for modulating angiogenesis in vivo, ex vivo or in vitro. More particularly, the invention relates to a soluble CD 146 protein usable in the context of human therapy, as well as to corresponding antibodies. Particular forms of CD 146, herein described, may be used to mobilize, in vivo or ex vivo, both mature and immature endothelial cells, as well as to increase their influence on angiogenesis. The invention also relates to compositions comprising such compounds, particularly pharmaceutical or diagnostic compositions, including kits and the like, as well as methods of therapy or diagnosis using said compounds, compositions and cells.