A T cell is a type of lymphocyte, which develops in the thymus gland and plays a central role in the immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor on the cell surface; these immune cells originate as precursor cells, derived from bone marrow, develop into several distinct types of T cells once they have migrated to the thymus gland. T cell differentiation continues after they have left the thymus. Groups of specific, differentiated T cells have an important role in controlling and shaping the immune response by providing a variety of immune-related functions. One of these functions is immune-mediated cell death, it is carried out by T cells in several ways: CD8+ T cells known as "killer cells", are cytotoxic - this means that they are able to directly kill virus-infected cells as well as cancer cells. CD8+ T cells are able to utilize small signalling proteins, known as cytokines, to recruit other cells when mounting an immune response.
A different population of T cells, the CD4+ T cells, function as "helper cells". Unlike CD8+ killer T cells, these CD4+ helper T cells function by indirectly killing cells identified as foreign: they determine if and how other parts of the immune system respond to a specific, perceived threat. Helper T cells use cytokine signalling to influence regulatory B cells directly, other cell populations indirectly. Regulatory T cells are yet another distinct population of these cells that provide the critical mechanism of tolerance, whereby immune cells are able to distinguish invading cells from "self" - thus preventing immune cells from inappropriately mounting a response against oneself. For this reason these regulatory T cells have been called "suppressor" T cells; these same self-tolerant cells are co-opted by cancer cells to prevent the recognition of, an immune response against, tumour cells. All T cells originate from c-kit + Sca1 + haematopoietic stem cells. In some cases, the origin might be the fetal liver during embryonic development.
The HSC differentiate into multipotent progenitors which retain the potential to become both myeloid and lymphoid cells. The process of differentiation proceeds to a common lymphoid progenitor, which can only differentiate into T, B or NK cells; these CLP cells migrate via the blood to the thymus, where they engraft. The earliest cells which arrived in the thymus are termed double-negative, as they express neither the CD4 nor CD8 co-receptor; the newly arrived CLP cells are CD4-CD8-CD44+CD25-ckit+ cells, are termed early thymic progenitors cells. These cells will undergo a round of division and downregulate c-kit and are termed DN1 cells. At the DN2 stage, cells upregulate the recombination genes RAG1 and RAG2 and re-arrange the TCRβ locus, combining V-D-J and constant region genes in an attempt to create a functional TCRβ chain; as the developing thymocyte progresses through to the DN3 stage, T cell expresses an invariant α-chain called pre-Tα alongside the TCRβ gene. If the rearranged β-chain pairs with the invariant α-chain, signals are produced which cease rearrangement of the β-chain.
Although these signals require this pre-TCR at the cell surface, they are independent of ligand binding to the pre-TCR. If the pre-TCR forms the cell downregulates CD25 and is termed a DN4 cell; these cells undergo a round of proliferation and begin to re-arrange TCRα locus. Double-positive thymocytes migrate deep into the thymic cortex, where they are presented with self-antigens; these self-antigens are expressed by thymic cortical epithelial cells on MHC molecules on the surface of cortical epithelial cells. Only those thymocytes that interact with MHC-I or MHC-II will receive a vital "survival signal". All that cannot will die by "death by neglect"; this process ensures that the selected T cells will have an MHC affinity that can serve useful functions in the body. The vast majority of developing thymocytes will die during this process; the process of positive selection takes a number of days. A thymocyte's fate is determined during positive selection. Double-positive cells that interact well with MHC class II molecules will become CD4+ cells, whereas thymocytes that interact well with MHC class I molecules mature into CD8+ cells.
A T cell becomes a CD4+ cell by down-regulating expression of its CD8 cell surface receptors. If the cell does not lose its signal, it will continue downregulating CD8 and become a CD4+, single positive cell; this process does not remove thymocytes. The autoimmune cells are removed by the process of negative selection, which occurs in the thymic medulla. Negative selection removes thymocytes that are capable of binding with "self" MHC peptides. Thymocytes that survive positive selection migrate towards the boundary of the cortex and medulla in the thymus. While in the medulla, they are again presented with a self-antigen presented on the MHC complex of medullary thymic epithelial cells. MTECs must be AIRE+ to properly express self-antigens from all tissues of the body on their MHC class I peptides; some mTECs are phagocytosed by thymic dendritic cells. Thym
Cornsay is a hamlet and civil parish in County Durham, England. The population of the Civil Parish taken at the 2011 census was 1,128, it is 6 miles southeast of Consett and 7 miles southwest of Durham. It consists including four farms & is the home of Greenacres nudist club. All belonged to Ushaw College for the training of Catholic priests, hence the organised nomenclature. East and West Farms are now in private hands as homes but the other two are still active, South Farm run by the Suddes family and North Farm by the Tweddle family. On the village green is the enigmatic "draw well": on first look a bus shelter but, on closer inspection, a building with a 17th-century dedication, it was once the main source of water for the village, a site for the sale of paraffin at a time when the village was larger. It was restored in 2007 by the removal of a breeze-block infill that had blocked the doorway and now has a new wrought-iron gate that allows inspection of the interior of the building. See Cornsay Colliery.
Media related to Cornsay at Wikimedia Commons
Hang Seng Bank Limited is a Hong Kong-based banking and financial services company with headquarters in Central, Hong Kong. It is one of Hong Kong's leading public companies in terms of market capitalisation and is part of the HSBC Group, which holds a majority equity interest in the bank. Hang Seng Bank is a commercial bank whose major business activities include retail banking, wealth management, commercial banking, treasury services, private banking. Hang Seng Bank operates a network of around 260 service outlets in Hong Kong, it has a wholly owned subsidiary in mainland China, Hang Seng Bank Limited which has a network of 46 branches and sub branches. It established the Hang Seng Index as a public service in 1969 and this stock market index is now known as the primary indicator of the Hong Kong stock market. In 1933, business partners Lam Bing Yim, Ho Sin Hang, Sheng Tsun Lin, Leung Chik Wai founded Hang Seng Ngan Ho, the predecessor of Hang Seng Bank, in Hong Kong. Hang Seng means "ever-growing" in Cantonese.
It commenced business as a simple money-changing shop at 70 Wing Lok Street, Sheung Wan, on 3 March 1933. In 1952, Hang Seng Bank embarked on commercial banking. Hang Seng Bank turned into a public company in 1960. In 1965, Hang Seng Bank suffered from bank run of which depleted one-fourth of its deposits; because of that, The Hongkong and Shanghai Banking Corporation acquired a 51% interest of Hang Seng Bank increased to 62.14%, owned the controlling power of Hang Seng Bank. In 1969, the Hang Seng Index was introduced as a public service; the index is now known as the indicator of the Hong Kong stock market. Hang Seng Bank was listed on the Hong Kong Stock Exchange in 1972. In 1981, Hang Seng Bank was given permission to run branches in MTR stations. Hang Seng Bank began to extend its business to China in 1985, with the opening of a representative office in Shenzhen. 10 years Hang Seng Bank opened its first Chinese branch in Guangzhou. In 2002, Hang Seng Bank launched personal e-Banking in Mainland China.
Hang Seng Bank opened its branch in Macau in 2003. In 2006, Hang Seng Bank received authorisation to get ready for the formation of its mainland China subsidiary bank. Within the same year, Hang Seng Bank introduced a brand revitalisation program and presented a new company slogan – Managing wealth for you, with you; the year, 2007 was significant to Hang Seng Bank. The China Banking Regulatory Commission authorised the formation of Hang Seng Bank Limited, the mainland China subsidiary bank of Hang Seng Bank. Which was established on 28 May 2007. In November, Hang Seng Bank opened its new Hong Kong office at Kowloon Bay. Hang Seng Bank became the first bank in Hong Kong to fix the renminbi prime rate in 2010. In February 2012, Hang Seng Bank introduced the world's first RMB gold exchange-traded fund; the brand value of Hang Seng Bank was ranked 65th globally in the 2012 Brand Finance Banking 500, the highest ranking for Hong Kong banks. Hang Seng Bank is a commercial bank whose major business activities include retail banking and wealth management and commercial banking, treasury services, private banking.
Hang Seng Bank operates a network of around 260 service outlets in Hong Kong. Hang Seng Bank is the only local bank to offer extensive branch services along Mass Transit Railway stations to better serve its customers. Hang Seng Bank established its wholly owned subsidiary Hang Seng Bank Limited in 2007; the subsidiary runs a mainland China network of 46 outlets in Beijing, Guangzhou, Dongguan, Nanjing, Ningbo, Kunming, Zhongshan, Xiamen and Jiangmen with 12 branches and 34 sub-branches. For foreign currency wholesale business, Hang Seng Bank maintains branches in Shenzhen and Singapore, a representative office in Taipei; the current chairman is Dr. Raymond Ch'ien Kuo Fung; the current Vice-Chairman and chief executive officer is Ms. Louisa Cheang. Hang Seng Bank official website