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Medullary Thymic Epithelial Cells
Medullary thymic epithelial cells (mTECs) represent a unique stromal cell population of the thymus which plays an essential role in the establishment of central tolerance. Therefore, mTECs rank among cells relevant for the development of functional mammal immune system. T cell precursors rise in bone marrow and migrate through the bloodstream to the thymus for further development. During their maturation in the thymus, they undergo a process called V(D)J recombination which conducts the development of T-cell receptor, T cell receptors (TCRs). The mechanism of this stochastic process enables on one hand the generation of vast repertoire of TCRs, however, on the other hand causes also origin of so called "autoreactive T cells" which recognize self antigens via their TCRs. Autoreactive T cells must be eliminated from the body or skewed into the Regulatory T cell, T Regulatory cells (TRegs) lineage to prevent manifestations of autoimmunity. mTECs possess the ability to deal with thes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thymic Selection
A thymocyte is an immune cell present in the thymus, before it undergoes transformation into a T cell. Thymocytes are produced as stem cells in the bone marrow and reach the thymus via the blood. Thymopoiesis describes the process which turns thymocytes into mature T cells according to either negative or positive selection. This selection process is vitally important in shaping the population of thymocytes into a peripheral pool of T cells that are able to respond to foreign pathogens but remain tolerant towards the body's own antigens. Positive selection selects cells which are able to bind MHC class I or II molecules with at least a weak affinity. This eliminates (by a process called "death by neglect") those T cells which would be non-functional due to an inability to bind MHC. Negative selection destroys thymocytes with a high affinity for self peptides or MHC. This eliminates cells which would direct immune responses towards self-proteins in the periphery. Negative selection i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
NF-κB
Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a family of transcription factor protein complexes that controls transcription (genetics), transcription of DNA, cytokine production and cell survival. NF-κB is found in almost all animal cell types and is involved in cellular responses to stimuli such as stress, cytokines, free radicals, heavy metals, ultraviolet irradiation, oxidized LDL, and bacterial or viral antigens. NF-κB plays a key role in regulating the immune response to infection. Incorrect regulation of NF-κB has been linked to cancer, inflammatory and autoimmune diseases, septic shock, viral infection, and improper immune development. NF-κB has also been implicated in processes of synaptic plasticity and memory. Discovery NF-κB was discovered by Ranjan Sen in the lab of Nobel laureate David Baltimore via its interaction with an 11-base pair sequence in the immunoglobulin light-chain Enhancer (genetics), enhancer in B cells. Later work ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Progenitor Cell
A progenitor cell is a biological cell that can differentiate into a specific cell type. Stem cells and progenitor cells have this ability in common. However, stem cells are less specified than progenitor cells. Progenitor cells can only differentiate into their "target" cell type. The most important difference between stem cells and progenitor cells is that stem cells can replicate indefinitely, whereas progenitor cells can divide only a limited number of times. Controversy about the exact definition remains and the concept is still evolving. The terms "progenitor cell" and "stem cell" are sometimes equated. Properties Most progenitors are identified as oligopotent. In this point of view, they can compare to adult stem cells, but progenitors are said to be in a further stage of cell differentiation. They are "midway" between stem cells and fully differentiated cells. The kind of potency they have depends on the type of their "parent" stem cell and also on their niche. Some ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endoderm
Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm. The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of multiple systems. In plant biology, endoderm corresponds to the innermost part of the cortex ( bark) in young shoots and young roots often consisting of a single cell layer. As the plant becomes older, more endoderm will lignify. Production The following chart shows the tissues produced by the endoderm. The embryonic endoderm develops into the interior linings of two tubes in the body, the digestive and respiratory tube. Liver and pancreas cells are believed to derive from a common precursor. In humans, the endoderm can differentiate into distinguishable organs after 5 w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pharyngeal Pouch (embryology)
In the embryonic development of vertebrates, pharyngeal pouches form on the endodermal side between the pharyngeal arches. The pharyngeal grooves (or clefts) form the lateral ectodermal surface of the neck region to separate the arches. Specific pouches First pouch The endoderm lines the future auditory tube (pharyngotympanic Eustachian tube), middle ear, mastoid antrum, and inner layer of the tympanic membrane. Derivatives of this pouch are supplied by Mandibular nerve. Second pouch * Contributes the middle ear, palatine tonsils, supplied by the facial nerve. Third pouch * The third pouch possesses dorsal and ventral wings. Derivatives of the dorsal wings include the inferior parathyroid glands, while the ventral wings fuse to form the cytoreticular cells of the thymus. The main nerve supply to the derivatives of this pouch is cranial nerve IX, glossopharyngeal nerve. Fourth pouch Derivatives include: * superior parathyroid glands and ultimobranchial body which forms the paraf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hassall's Corpuscles
Hassall's corpuscles (also known as thymic bodies) are structures found in the medulla of the human thymus, formed from eosinophilic type VI thymic epithelial cells arranged concentrically. These concentric corpuscles are composed of a central mass, consisting of one or more granular cells, and of a capsule formed of epithelioid cells. They vary in size with diameters from 20 to more than 100μm, and tend to grow larger with age. They can be spherical or ovoid and their epithelial cells contain keratohyalin and bundles of cytoplasmic fibres. Later studies indicate that Hassall's corpuscles differentiate from medullary thymic epithelial cells after they lose autoimmune regulator (AIRE) expression. This makes them an example of Thymic mimetic cells. They are named for Arthur Hill Hassall, who discovered them in 1846. The function of Hassall's corpuscles is currently unclear, and the absence of this structure in the thymus of most murine species (except for the New Zealand White ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thymic Mimetic Cells
Thymic mimetic cells are a heterogeneous population of cells located in the thymus that exhibit phenotypes of a wide variety of differentiated peripheral cells. They arise from medullary thymic epithelial cells (mTECs) and also function in negative selection of self-reactive T cells. History Some subsets of these cells were observed as early as the mid-1800s because of their distinct, seemingly misplaced, phenotype. The most readily observed subsets were those accumulating and forming microscopic structures, most notably Hassall's corpuscles resembling skin keratinocytes. Many subsets with a more dispersed distribution were found later. Substantial progress has been made in recent years owing to the rapid development of single cell sequencing methods, such as scRNA-seq or scATAC-seq. Diversity Although thymic mimetic cells exhibit transcriptional programmes of cells from other tissues, they are not identical to them and share a part of their gene expression with mTECs from w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dendritic Cell
A dendritic cell (DC) is an antigen-presenting cell (also known as an ''accessory cell'') of the mammalian immune system. A DC's main function is to process antigen material and present it on the cell surface to the T cells of the immune system. They act as messengers between the innate and adaptive immune systems. Dendritic cells are present in tissues that are in contact with the body's external environment, such as the skin, and the inner lining of the nose, lungs, stomach and intestines. They can also be found in an immature and mature state in the blood. Once activated, they migrate to the lymph nodes, where they interact with T cells and B cells to initiate and shape the adaptive immune response. At certain development stages they grow branched projections, the '' dendrites,'' that give the cell its name (δένδρον or déndron being Greek for 'tree'). While similar in appearance to the dendrites of neurons, these are structures distinct from them. Immature dendr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apoptosis
Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biology), morphology) and death. These changes include Bleb (cell biology), blebbing, Plasmolysis, cell shrinkage, Karyorrhexis, nuclear fragmentation, Pyknosis, chromatin condensation, Apoptotic DNA fragmentation, DNA fragmentation, and mRNA decay. The average adult human loses 50 to 70 1,000,000,000, billion cells each day due to apoptosis. For the average human child between 8 and 14 years old, each day the approximate loss is 20 to 30 billion cells. In contrast to necrosis, which is a form of traumatic cell death that results from acute cellular injury, apoptosis is a highly regulated and controlled process that confers advantages during an organism's life cycle. For example, the separation of fingers and toes in a developing human embryo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antigen-presenting Cell
An antigen-presenting cell (APC) or accessory cell is a Cell (biology), cell that displays an antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation. T cells may recognize these complexes using their T cell receptors (TCRs). APCs antigen processing, process antigens and present them to T cells. Almost all cell types can present antigens in some way. They are found in a variety of tissue types. Dedicated antigen-presenting cells, including macrophages, B cells and dendritic cells, present foreign antigens to T helper cell, helper T cells, while virus-infected cells (or cancer cells) can present antigens originating inside the cell to cytotoxic T cells. In addition to the MHC family of proteins, antigen presentation relies on other specialized signaling molecules on the surfaces of both APCs and T cells. Antigen-presenting cells are vital for effective Adaptive immune system, adaptive immune response, as the fun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cortical Thymic Epithelial Cells
Cortical thymic epithelial cells (cTECs) form unique parenchyma cell population of the thymus which critically contribute to the development of T cells. Thymus Tissue (biology), tissue is compartmentalized into cortex and medulla and each of these two compartments comprises its specific thymic epithelial cell subset. cTECs reside in the outer part- cortex, which mostly serves as a developmental site for T cells. Precursor cell, Precursors of T cells originate in the bone marrow from which they migrate via bloodstream into thymic cortex, where they encounter stromal cells including cTECs, which form the microenvironment crucial for proliferation and development of T cells by expression of DLL4 (delta-like notch ligand 4), cytokines Interleukin 7, IL-7, Transforming growth factor beta, TGFβ or stem cell factor and chemokines CCL25, Stromal cell-derived factor 1, CXCL12 or CCRL1 etc. Essential part of T cell development forms process called V(D)J recombination, VDJ recombination, m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T Cell Positive Selection
T, or t, is the twentieth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''tee'' (pronounced ), plural ''tees''. It is derived from the Semitic Taw 𐤕 of the Phoenician and Paleo-Hebrew script (Aramaic and Hebrew Taw ת/𐡕/, Syriac Taw ܬ, and Arabic ت Tāʼ) via the Greek letter τ (tau). In English, it is most commonly used to represent the voiceless alveolar plosive, a sound it also denotes in the International Phonetic Alphabet. It is the most commonly used consonant and the second-most commonly used letter in English-language texts. History ''Taw'' was the last letter of the Western Semitic and Hebrew alphabets. The sound value of Semitic ''Taw'', the Greek alphabet Tαυ (''Tau''), Old Italic and Latin T has remained fairly constant, representing in each of these, and it has also kept its original basic shape in most of these alphabets. Us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
