Lymph node lymphatic vessels- function and regulation

Abstract

Lymph nodes (LNs) are the major secondary lymphoid organs spatially distributed all over the human and mouse body playing a major role in innate and adaptive immune reactions. Like most other organs LNs have both blood and lymphatic vessels as major components of vasculature. Blood vessels function in providing nourishment, recruitment of B and T lymphocytes and monocytes to lymph nodes. Lymphatic vessels, the main topic of this research, function as conduits of lymph fluid from periphery along with APC carrying one or more types of antigens. Thus LN lymphatic vessels play a major role in early innate immune reactions and greatly aid in generating later course of adaptive immune reactions. Lymphatic vessels are present in the sinusoidal form in LNs. The peripheral afferent lymphatic vessels attach to the LN capsule and spread below the capsule as sinusoidal network known as sub-capsular lymphatic vessels. In normal condition very few sub-capsular lymphatic vessels extend from the capsule and grow into the paracortex, deep cortex reaching the medullary lymphatic vessels. Around the hilus region the medullary and sub-capsular lymphatic vessels merge and leave the LNs as a single efferent lymphatic vessel. This way lymphatic vessels form labyrinth of sinusoids in LNs harboring one or more types of macrophages tethered along with them. When the lymph from the peripheral tissues enters the LN via afferent lymphatic vessels the antigen is captured by the sub-capsular, medullary vessel macrophages and the antigen free lymph leaves the LN via efferent lymphatic vessel. Antigen from the macrophage is processed and presented to the specific lymphocytes directly or via dendritic cells. Other than this, most of the times peripheral tissue dendritic cells, langerhans cells (skin) carry the antigen directly to the lymphocytes migrating via afferent lymphatic vessels outside the LN and LN lymphatic vessels inside the LNs. This way LN lymphatic vessels play a vital role in ...