Cells and tissues of the immune system (original) (raw)
The conduit system of the lymph node
International Immunology, 2008
The lymphoid compartment of lymph nodes is impermeable to many molecules that are delivered via afferent lymphatic vessels. In the lymphoid compartment, fibroblast reticular cells form an interconnected network-the conduit system. This network has a structural function supporting tightly packed lymphocytes and antigen-presenting cells; however, it also has an important function as a molecular sieve, since it contains tubules that are the only entry point for fluid and allow only small molecules and particles (including antigens) to flow along the network. This size exclusion may prevent pathogens entering the blood from lymph. Dendritic cells can sample antigens from the conduit system and present them to nearby lymphocytes; this may be particularly important in initiating immune responses. The importance of larger antigen transport via macrophages or other cells is unclear. Lymphocytes and antigen-presenting dendritic cells actively move and interact along the conduit system, perhaps in response to chemokines or cytokines transported by the conduit system; these molecules may also be transported to high endothelial venules and regulate the attraction of blood leukocytes to the lymph nodes. The conduit system is also important for fluid distribution between afferent lymphatics and blood, but the mechanisms are not yet established.
Acta Histochemica, 2007
The function of lymph nodes is greatly influenced by their unique microanatomy, in which distinct subpopulations of cells are compartmentalized by a meshwork of reticular cells and fibres, specialized blood and lymphatic vessels and nerves. Using antibodies against extracellular matrix (ECM) proteins (fibronectin, collagen IV and laminin), proteoglycan (perlecan), and a fibroblastic marker (ERTR-7), the distribution and molecular organization of the system of reticular fibres was investigated by three-dimensional (3D) reconstruction methods. Fibronectin, collagen IV and laminin are restricted to reticular fibres and have a similar distribution pattern, whereas perlecan is limited to the vascular system of the lymph node. Various compartments of the lymph node, such as the B-cell follicle, paracortex (including the high endothelial venules and paracortical cord), and medulla have been reconstructed to visualize their vasculature with respect to B and T cells. Since the morphology of lymph nodes may change significantly in pathological conditions, different compartments of reactive lymph node (after low-dose Listeria monocytogenes infection), especially germinal centres, were also investigated. The data presented here should facilitate our understanding of the 3D organization of non-immune cell components of lymph nodes, which is crucial for cell adhesion, migration, activation, and differentiation in normal and pathological conditions.
Fine structure of lymph pathways in nodes from the superficial inguinal lymph centre in the pig
Journal of anatomy, 1989
In the pig lymph node most lymph passes from afferent lymphatics to trabecular sinuses in centrally located dense nodular tissue. The lining of these sinuses is continuous adjacent to the trabecula but it is interrupted by numerous gaps adjacent to the parenchyma. Where the trabeculae end, their associated sinuses are continuous with the many interstitial spaces, up to 10 microns across, in the diffuse tissue. Lymph percolates through these spaces and is directly exposed to large numbers of macrophages with elaborate cytoplasmic veils and to reticular fibres which could be involved in antigen retention. Parts of the diffuse tissue are arranged into sinuses and cords in a manner similar to the medullary tissue in other species and a subcapsular sinus is also present over the diffuse tissue. There are gaps in the lining of these sinuses through which they communicate with the interstices of the parenchyma. Lymph flows from the sinuses in the diffuse tissue into efferent lymph vessels;...
Cytokine, 2012
The blood and lymphatic systems are the two well-established circulatory systems. The existence of a third circulatory system representing acupuncture meridians was claimed in the 1960s. The very existence and function of the system, however, remained uncertain. We have found that microscopic nodes and ducts inside lymphatics, as well as on the surface of internal organs of the rat. The nodes and ducts are covered by a layer of EMP-3-positive spindle-shaped epithelium with, below, a layer of vWF-positive but CD31-negative endothelium. The nodes contain a variety of immune cells, usually enriched with mast cells, eosinophils, neutrophils and histiocytes, as well as chromaffin cells, other granule-containing cells. Secretory granules originating from the mast cells in the nodes appear to pass along ductules, two or more of which make up a duct. Our results reveal a potential circulatory system whose anatomical structure and cellular content differ from the blood and lymph systems, and which may be involved in the transport of secretory granules.
Immunity, 2005
can phagocytose antigens and, subsequently, traffic via 22185 Lund the afferent lymphatics into the T cell area of the draining Sweden lymph node to initiate immune responses (Cavanagh 2 Department of Dermatology and Von Andrian, 2002; Manickasingham and Reis e University of Erlangen Sousa, 2001; Randolph, 2001). This pathway is well char-91052 Erlangen acterized, and there is recent evidence that steady state Germany migration of DC into the lymph node also occurs in 3 Department of Experimental Medicine I the healthy organism, which may serve to continuously University of Erlangen tolerize T cells against self antigens (Lutz and Schuler, 91054 Erlangen 2002; Steinman et al., 2003). A second pathway of anti-Germany gen delivery is less well defined and functions indepen-4 Department of Anatomy and Cell Biology dently of cellular trafficking along the lymphatics. Sev-McGill University eral studies have shown that peripherally applied Montreal H3A 2B2 soluble antigen is taken up, presented, and cross pre-Canada sented by resident DC in the T cell area of the draining 5 Department of Functional and Applied Anatomy lymph node. This happens before there is any detectable Medical School of Hannover immigration of DC from the periphery (Ingulli et al., 2002; 30625 Hannover Itano et al., 2003; Maurer et al., 2002; Pior et al., 1999). Germany
The architecture of rat lymph nodes
Anatomy and Embryology, 1983
Non-lymphoid cells in rat lymph nodes are described as seen by combined light and electron microscopy of normal adult, congenitally athymic, germ-free, irradiated, or newborn rats. The cells are divided into stromal and non-stromal. The latter category consists of a variety of morphologically distinct cell types with characteristic distribution patterns. The presence of paracortical interdigitating cells in lymph nodes of germ-free rats, athymic rats, and newborn euthymic and athymic rats, refutes the ideas that interdigitating cells differentiate from macrophages under immune stimulation or T cell influences. Follicular dendritic cells are more clearly visualized and appear to be polynucleated after emptying the follicles of lymphoid cells by irradiation. Follicular dendritic cells and tingible body macrophages are found in conventionally raised euthymic and athymic rats, but not in germ-free rats. The interrelationships of these and other types of non-lymphoid cells are discussed.
Differential Expression of Basement Membrane Components in Lymphatic Tissues
Journal of Histochemistry and Cytochemistry, 2004
Peripheral lymphoid tissues act as important organs of immunological defense. Characteristic of their architecture is the rich reticular fiber meshwork composed of various extracellular matrix (ECM) molecules with which the stationary non-lymphatic cells stay in intimate contact and form channels through which the lymphatic cells travel. Here we studied the distribution of various laminin (Ln) chains and different types of collagens in human spleen, lymph node, and tonsil to clarify their chain-specific distribution. The most widely distributed proteins in all these organs were Ln chains alpha5, beta1, gamma1 and collagen types IV and XVIII, which were present in practically all compartments. Conversely, Ln alpha1, alpha2, alpha4, and type VII collagen showed a more restricted expression pattern. A unique feature was that Ln alpha3-, beta3-, and gamma2-chains, which normally are not localized to the vascular wall in non-lymphatic tissues, were present also in capillary basement membranes (BMs) of the follicular structures of lymph node and tonsil and in Ln alpha1-chain and type VII collagen also in the splenic white pulp. We also found that collagen XVII was exclusively present in the ring fibers of the spleen. The results indicate that BMs of lymphatic tissues contain a variety of macromolecules that probably contribute strongly to immunological events. In addition, capillaries of the lymphoid tissue exhibit a specified BM composition resembling that in epithelial BMs of non-lymphoid tissues.