lymphocyte


lymphocyte
lymphocytic /lim'feuh sit"ik/, adj.
/lim"feuh suyt'/, n. Anat.
a type of white blood cell having a large, spherical nucleus surrounded by a thin layer of nongranular cytoplasm. Cf. B cell, T cell.
[1885-90; LYMPHO- + -CYTE]

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Type of leukocyte fundamental to the immune system, regulating and participating in acquired immunity.

Each has receptor molecules on its surface that bind to a specific antigen. The two primary types, B cells and T cells, originate from stem cells in bone marrow and travel to lymphoid tissues. When a B cell binds to an antigen, it multiplies to form a clone of identical cells. Some of these, acted on by helper T cells, differentiate into plasma cells that produce antibodies against the antigen. Others (memory cells) multiply, providing long-term immunity to the antigen.

Human lymphocyte (phase-contrast microphotograph).

Manfred Kage
Peter Arnold

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 type of leukocyte (white blood cell) that is of fundamental importance in the immune system because lymphocytes are the cells that determine the specificity of the immune response to infectious microorganisms and other foreign substances. In humans lymphocytes make up 25 to 33 percent of the total number of leukocytes. They are found in the circulation and also are concentrated in central lymphoid organs and tissues, such as the spleen, tonsils, and lymph nodes, where the initial immune response is likely to occur.

      The two primary types of lymphocytes are B lymphocytes (B cell) and T lymphocytes, or B cells and T cells. Both originate from stem cells in the bone marrow and are initially similar in appearance. Some lymphocytes migrate to the thymus, where they mature into T cells; others remain in the bone marrow, where—in humans—they develop into B cells. Most lymphocytes are short-lived, with an average life span of a week to a few months, but a few live for years, providing a pool of long-lived T and B cells. These cells account for immunologic “memory,” a more rapid, vigorous response to a second encounter with the same antigen.

 Through receptor molecules on their surfaces, lymphocytes are able to bind antigens (antigen) (foreign substances or microorganisms that the host recognizes as “nonself”) and help remove them from the body. Each lymphocyte bears receptors that bind to a specific antigen. The ability to respond to virtually any antigen comes from the enormous variety of lymphocyte populations that the body contains, each of them with a receptor capable of recognizing a unique antigen.

 Once stimulated by binding to a foreign antigen, such as a component of a bacterium or virus, a lymphocyte multiplies into a clone of identical cells. Some of the cloned B cells differentiate into plasma cells that produce antibody molecules. These antibodies are closely modeled after the receptors of the precursor B cell, and, once released into the blood and lymph, they bind to the target antigen and initiate its neutralization or destruction. Antibody production continues for several days or months, until the antigen has been overcome. Other B cells, the memory B cells, are stimulated to multiply but do not differentiate into plasma cells; they provide the immune system with long-lasting memory.

 In the thymus, T cells multiply and differentiate into helper, regulatory, or cytotoxic T cells or become memory T cells. They are then seeded to peripheral tissues or circulate in the blood or lymphatic system. Once stimulated by the appropriate antigen, helper T cells secrete chemical messengers called cytokines (cytokine), which stimulate the differentiation of B cells into plasma cells, thereby promoting antibody production. Regulatory T cells act to control immune reactions, hence their name. Cytotoxic T cells, which are activated by various cytokines, bind to and kill infected cells and cancer cells.
 

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Universalium. 2010.

Look at other dictionaries:

  • lymphocyte — [ lɛ̃fɔsit ] n. m. • 1900; de lympho et cyte ♦ Méd. Petit leucocyte à gros noyau non segmenté, présent dans le sang, la moelle et les tissus lymphoïdes (ganglions lymphatiques, rate) et jouant un rôle important dans le processus d immunité (⇒… …   Encyclopédie Universelle

  • Lymphocyte T4 — Lymphocyte T auxiliaire Les cellules CD4+ (en anglais T Helper), parfois appelés lymphocytes T4 ou plus précisément lymphocytes Th à CD4 positif, sont un type original différencié des autres lymphocytes T, non phagocytaires, agissant seulement… …   Wikipédia en Français

  • Lymphocyte B — ● Lymphocyte B lymphocyte des lignées de cellules immunocompétentes productrices d anticorps circulants …   Encyclopédie Universelle

  • Lymphocyte T — ● Lymphocyte T lymphocyte dérivant du thymus qui participe aux réactions immunitaires dites à « médiation cellulaire » …   Encyclopédie Universelle

  • lymphocyte — lymphocyte. См. лимфоцит. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • lymphocyte — cell found in the lymph, 1890, from L. lympho (see LYMPH (Cf. lymph)) + cyte (see CYTO (Cf. cyto )) …   Etymology dictionary

  • lymphocyte — ► NOUN ▪ a form of small leucocyte (white blood cell) with a single round nucleus, occurring especially in the lymphatic system …   English terms dictionary

  • lymphocyte — [lim′fō sīt΄] n. [ LYMPHO + CYTE] a nongranular variety of leukocyte formed in lymphatic tissue, important in the synthesis of antibodies: see B CELL lymphocytic [lim′fōsit′ik] adj …   English World dictionary

  • Lymphocyte — Un lymphocyte, vu par un microscope électronique à balayage. Les lymphocytes sont des leucocytes qui ont un rôle majeur dans le système immunitaire. En termes de structure et de fonction, on distingue deux lignées lymphocytaires différentes  …   Wikipédia en Français

  • Lymphocyte — A lymphocyte is a type of white blood cell in the vertebrate immune system. By their appearance under the light microscope, there are two broad categories of lymphocytes, namely the large granular lymphocytes and the small lymphocytes.… …   Wikipedia

  • Lymphocyte T — Les lymphocytes T, ou cellules T, sont une catégorie de lymphocytes qui jouent un grand rôle dans la réponse immunitaire secondaire. « T » est l abréviation de thymus, l organe dans lequel leur développement s achève. Ils sont… …   Wikipédia en Français


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