Regulatory mechanisms in lymphatic vessel contraction under normal and inflammatory conditions

The lymphatic system is composed of a dense network of lymphatic vessels, which are critical components of physiological interstitial fluid transport. These vessels possess intrinsic contractile properties providing the driving force for the fluid to be drained away from the tissues and propelled, as lymph, back into the bloodstream. Lymphatic pumping is also important to carry immune cells, bacteria, macromolecules, viruses and their products to and through lymph nodes, the other component of the lymphatic system, to initiate the adaptive immune response. In addition, among the many circulating mediators known to modulate lymphatic contractile activity and thus lymph flow, mediators of inflammation have potent excitatory or inhibitory actions. The involvement of lymphatic vessels in edema resolution, immune cell trafficking and their sensitivity to inflammatory mediators make them pivotal players of the inflammation process. The ability of lymphatic vessels to generate and regulate lymph flow is provided by the lymphatic muscle present in the vessels' wall. Although molecular studies investigating the mechanisms of lymphatic vessel contraction are still very limited, recent findings suggest that lymphatic pumping requires complicated muscle activities that have similarities to those seen in both the heart (striated muscle) and blood vessels (smooth muscle). This review article focuses on presenting and discussing the mechanisms that regulate lymphatic vessel contraction under normal and pathophysiological states, specifically pertaining to inflammatory conditions.