Gastrointestinal lymphatics in health and disease

Abstract

Lymphatics perform essential transport and immune regulatory functions to maintain homeostasis in the gastrointestinal (GI) system. Although blood and lymphatic vessels function as parallel and integrated systems, our understanding of lymphatic structure, regulation and functioning lags far behind that of the blood vascular system. This chapter reviews lymphatic flow, differences in lymphangiogenic and hemangiogenic factors, lymphatic fate determinants and structural features, and examines how altered molecular signaling influences lymphatic function in organs of the GI system. Innate errors in lymphatic development frequently disturb GI functioning and physiology. Expansion of lymphatics, a prominent feature of GI inflammation, may also play an important role in tissue restitution following injury. Destruction or dysregulation of lymphatics, following injury, surgery or chronic inflammation also exacerbates GI disease activity. Understanding the physiological roles played by GI lymphatics is essential to elucidating their underlying contributions to forms of congenital and acquired forms of GI pathology, and will provide novel approaches for therapy.

Figure 1

a) Small intestine lymphatics. Small intestinal villous lacteals in the center of each villus, b) large intestine lymphatics. Large intestine lacks lymphatic lacteals but is supplied with lymphatic vessels.

Figure 2

Lymphatics in liver. Lymph filtered into the space of Disse (peri-sinusoidal) drains to deep lymphatics in the hepatic parenchyma associated with portal triads.

Figure 3

Enhanced lymphatics in IBD. Increased lymphatic abundance (D2–40⁺ staining) is seen in Crohn’s disease (panel 2) and ulcerative colitis (panel 3), compared to normal controls (panel 1).