Angiogenesis-Regulating Cytokines

The establishment and maintenance of a vascular supply is an absolute requirement for the growth of normal and neoplastic tissues, and as might be predicted, the cardiovascular system is the first organ system to develop and to become functional during embryogenesis. Both during development and in postnatal life, all new blood vessels begin as simple endothelial-lined tubes. Some become capillaries after developing an intimate association with pericytes, whereas others develop into vessels of larger diameter (arteries and veins) and acquire a variable number of concentrically disposed smooth-muscle cell layers. Traditionally, the formation of new blood vessels has been ascribed to two interrelated but separable processes, vasculogenesis, and angiogenesis (Fig. 1).