Lymph formation, composition and circulation: a proteomics perspective.

During the last 20 years a deeper understanding of the lymphatic circulatory system, lymph formation and composition has emerged. This review will examine the current knowledge on the organization of the lymphatic vascular tree, the formation of lymph from the extracellular fluid, lymph circulation and the lymph proteomic composition during physiological and pathological conditions. Formation of the lymph fluid is dependent on pressure gradients in the capillary beds and the composition of the endothelial cell glycocalyx, which acts as a molecular sieve. Fluid propulsion toward the draining node is dependent on the intrinsic pumping mechanism of the lymphangions and their unidirectional valves. The lymph 'omics' composition is dependent on the ultrafiltration of plasma proteins as well as proteins and molecules derived from the metabolic and catabolic activities of each parenchymal organ from which the lymph drains. Altogether, these new insights have brought about a new awareness of the importance of the lymphatic system in human physiology and pathology.