Lymphatic Vascular Development

This chapter focuses on the events that initiate and control construction of the lymphatic vasculature during embryonic development, and how these events are recapitulated or go wrong in disease processes. Lymphatic vessels are a vital but often overlooked component of the cardiovascular system. In contrast to blood vessels, lymphatic vessels do not deliver oxygen and nutrients to tissues, but instead collect and return interstitial fluid and protein to the bloodstream. In addition, lymphatic vessels provide an important trafficking route for cells of the immune system during immune surveillance and infection, and facilitate the absorption of lipids from the digestive tract. Lymphatic vascular function is critical for both embryonic development and adult homeostasis, reflected by the fact that abnormalities in the growth and development of lymphatic vessels (lymphangiogenesis) are associated with an ever-expanding catalog of human pathologies. Defects in embryonic lymphangiogenesis that result in dysfunctional lymphatic vessels are associated with congenital lymphoedema syndromes, as well as Down, Noonan's and Turner syndromes. It is likely that the most severe disturbances in embryonic lymphatic vascular development are incompatible with life. Aberrant postnatal lymphangiogenesis has recently been associated with inflammatory pathologies including graft rejection, asthma, psoriasis and arthritis, while the stimulation of lymphangiogenesis by tumors has been demonstrated to promote tumor metastasis in mouse models and has been correlated with poor patient prognosis in several types of human cancers.