A lymphocyte is one of the subtypes of a white blood cell in a vertebrate's immune system. Lymphocytes include natural killer cells, T cells, B cells, they are the main type of cell found in lymph, which prompted the name "lymphocyte". The three major types of lymphocyte are B cells and natural killer cells. Lymphocytes can be identified by their large nucleus. T cells and B cells are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity, whereas B cells are responsible for humoral immunity; the function of T cells and B cells is to recognize specific "non-self" antigens, during a process known as antigen presentation. Once they have identified an invader, the cells generate specific responses that are tailored maximally to eliminate specific pathogens or pathogen-infected cells. B cells respond to pathogens by producing large quantities of antibodies which neutralize foreign objects like bacteria and viruses. In response to pathogens some T cells, called T helper cells, produce cytokines that direct the immune response, while other T cells, called cytotoxic T cells, produce toxic granules that contain powerful enzymes which induce the death of pathogen-infected cells.
Following activation, B cells and T cells leave a lasting legacy of the antigens they have encountered, in the form of memory cells. Throughout the lifetime of an animal, these memory cells will "remember" each specific pathogen encountered, are able to mount a strong and rapid response if the same pathogen is detected again. NK cells are a part of the innate immune system and play a major role in defending the host from tumors and virally infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing changes of a surface molecule called MHC class I. NK cells are activated in response to a family of cytokines called interferons. Activated NK cells release cytotoxic granules which destroy the altered cells, they are named "natural killer cells" because they do not require prior activation in order to kill cells which are missing MHC class I. Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow; this process is called haematopoiesis.
All lymphocytes originate, during this process, from a common lymphoid progenitor before differentiating into their distinct lymphocyte types. The differentiation of lymphocytes follows various pathways in a hierarchical fashion as well as in a more plastic fashion; the formation of lymphocytes is known as lymphopoiesis. In mammals, B cells mature in the bone marrow, at the core of most bones. In birds, B cells mature in the bursa of Fabricius, a lymphoid organ where they were first discovered by Chang and Glick, not from bone marrow as believed. T cells mature in a distinct organ, called the thymus. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs where they survey for invading pathogens and/or tumor cells; the lymphocytes involved in adaptive immunity differentiate further after exposure to an antigen. Effector lymphocytes function to eliminate the antigen, either by releasing antibodies, cytotoxic granules or by signaling to other cells of the immune system.
Memory T cells remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure. Microscopically, in a Wright's stained peripheral blood smear, a normal lymphocyte has a large, dark-staining nucleus with little to no eosinophilic cytoplasm. In normal situations, the coarse, dense nucleus of a lymphocyte is the size of a red blood cell; some lymphocytes show a clear perinuclear zone around the nucleus or could exhibit a small clear zone to one side of the nucleus. Polyribosomes are a prominent feature in the lymphocytes and can be viewed with an electron microscope; the ribosomes are involved in protein synthesis, allowing the generation of large quantities of cytokines and immunoglobulins by these cells. It is impossible to distinguish between B cells in a peripheral blood smear. Flow cytometry testing is used for specific lymphocyte population counts; this can be used to determine the percentage of lymphocytes that contain a particular combination of specific cell surface proteins, such as immunoglobulins or cluster of differentiation markers or that produce particular proteins.
In order to study the function of a lymphocyte by virtue of the proteins it generates, other scientific techniques like the ELISPOT or secretion assay techniques can be used. In the circulatory system, they move from lymph node to lymph node; this contrasts with macrophages. A lymphocyte count is part of a peripheral complete blood cell count and is expressed as the percentage of lymphocytes to the total number of white blood cells counted. A general increase in the number of lymphocytes is known as lymphocytosis, whereas a decrease is known as lymphocytopenia. An increase in lymphocyte concentration is a sign of a viral infection (in some rare case, leukemias are found thro
Kendalia is an unincorporated community in northeastern Kendall County, United States. Kendalia lies at the intersection of RM 473 and FM 3351 northeast of the city of Boerne, the county seat of Kendall County, its elevation is 1,384 feet. Although Kendalia is unincorporated, it has a post office, with the ZIP code of 78027; the community is part of the San Antonio Metropolitan Statistical Area. Named for early nearby settler George Wilkins Kendall, the community was surveyed in 1883, although a post office was not established until 1895; the local economy has long been dependent on ranching, although many residents today work in cities such as Blanco or San Antonio. Ranch to Market Road 473 Farm to Market Road 3351 Profile of Kendalia from the Handbook of Texas Online
Vanishing of the Bees is a 2009 documentary film by Hive Mentality Films & Hipfuel Films, directed by George Langworthy and Maryam Henein and released in the United Kingdom in October 2009. The story is centered on the sudden disappearance of honey bees from beehives around the world, caused by the poorly understood phenomenon known as Colony Collapse Disorder or CCD. Although the film does not draw any firm scientific conclusions as to the precise cause or causes of CCD, it does suggest a link between neonicotinoid pesticides and CCD; the UK cinema release of the film was supported by The Co-operative Group. David Hackenberg as himself Michael Pollan as himself Simon Buxton as himself Emilia Fox as narrator Ellen Page as narrator The film was first released in the UK with a British narration by Emilia Fox and received mixed reviews from critics, achieving a rating of 62 percent on Rotten Tomatoes based on 13 reviews, with an average rating of 5.3/10. Filmstar called Vanishing of the Bees “The most important documentary film since An Inconvenient Truth.”
And Stuart McGurk of The Sunday Times wrote that while the "subject is serious", this film was "well intentioned and urgent", it was "let down by hammy narration, a made-for-TV budget". Philip French of The Observer called it a "serious, rather rambling documentary features some good, decent people", he added that "The blame falls principally on pesticides, genetic engineering and the world's changing landscape. Governments, the film charges, are listening more to the producers of chemicals than to beekeepers."The film was re-released in the US with a new edit and narration by Ellen Page. The film went on to win best documentary from the Idyllwild International Festival of Cinema and the Cosmic Cine Film Festival Vanishing of the Bees on IMDb Official website at the Wayback Machine Review of Vanishing of the Bees at Empireonline.com Retrieved 22 July 2010 Review of Vanishing of the Bees at www.guardian.co.uk Retrieved 22 July 2010