Lymph node stromal cell

Lymph node stromal cells are essential to the structure and function of the lymph node. There are a number of different types of lymph node stromal cells which have a number of functions including: creating a tissue scaffold within lymph nodes for the support of hematopoietic cells; the release of small molecules that are chemical messengers that facilitate interactions between hematopoietic cells; the facilitation of the migration of hematopoietic cells; the presentation of antigens to immune cells at the initiation of the adaptive immune system; and the homeostasis of lymphocyte numbers. Stromal cells originate from multipotent mesenchymal stem cells. Lymph node stromal cells are essential to the structure and function of the lymph node. There are a number of different types of lymph node stromal cells which have a number of functions including: creating a tissue scaffold within lymph nodes for the support of hematopoietic cells; the release of small molecules that are chemical messengers that facilitate interactions between hematopoietic cells; the facilitation of the migration of hematopoietic cells; the presentation of antigens to immune cells at the initiation of the adaptive immune system; and the homeostasis of lymphocyte numbers. Stromal cells originate from multipotent mesenchymal stem cells. Lymph nodes are enclosed in an external fibrous capsule and from this capsule, thin walls of sinew called trabeculae, penetrate into the lymph node, partially dividing it. Beneath the external capsule and along the courses of the trabeculae, are peritrabecular and subcapsular sinuses. These sinuses are cavities containing macrophages (specialised cells which help to keep the extracellular matrix in order). The interior of the lymph node has two regions: the cortex and the medulla. In the cortex, lymphoid tissue is organized into nodules. In the nodules, T lymphocytes (cells which help to fight viruses) are located in the T cell zone. B lymphocytes (cells which help to fight certain bacteria) are located in the B cell follicle. The primary B cell follicle matures in germinal centers. In the medulla are hematopoietic cells (which contribute to the formation of the blood) and stromal cells. Near the medulla is the hilum of lymph node. This is the place where blood vessels enter and leave the lymph node and lymphatic vessels leave the lymph node. Lymph vessels entering the node do so along the perimeter (outer surface). The lymph nodes, the spleen and Peyer's patches, are known as secondary lymphoid organs. Lymph nodes are found between lymphatic ducts and blood vessels. Afferent lymphatic vessels bring lymph fluid from the peripheral tissues to the lymph nodes. The lymph tissue in the lymph nodes consists of immune cells (95%), for example lymphocytes, and stromal cells (1% to 5%) The genesis of lymph nodes begins within the blood and the lymphatic system. Interactions between stromal and hematopoietic cells are important for the development of lymph nodes. Crosstalk LEC, lymphoid tissue inducer cells and mesenchymal stromal organizer cells initiate the formation of lymph nodes. Naive lymphocytes (those with no history of contact with antigens) travel from the bone marrow or high endothelial venules of the thymus where they develop as lymphoblasts, to lymph nodes, where they mature. The primary role of lymph node stromal cells is structural. They form a scaffold for hematopoietic cells and assist their movement along it. The molecular signaling systems (chemokines) that distribute lymphocytes to appropriate localities within the lymph node (T and B cell segregation) are also created by lymph node stromal cells. Lymphocytes have receptors for such chemokines. For example, Naive T cells express the CCR7 receptor for the chemokine CCL21. and B cells exhibit CXCR5 receptors for chemokine CXCL13. The lymph from the peripheral tissues contains soluble antigens and arrives at the lymph node via afferent lymphatic vessels. An adaptive immune response takes place in response to the presence of the antigen in the lymph node. Antigen-presenting cells accumulate near high endothelial venules to process soluble antigens. Antigens are also presented on the surface of dendritic cells. In an inflammatory state, lymphatic endothelial cells increase their surface adhesion molecules, and dendritic cells express a surface CCR7 receptor. This type of receptor interacts with the chemokine CCL21, produced by fibroblastic reticular cells. Due to this interaction, dendritic cells move to the T cell zone or to the B cell follicle along the fibroblast reticular cell network. Dendritic cells exhibit C-type lectin receptors (CLEC-2), which bind to gp38 on the surface of lymphatic endothelial cells.