Lymphocyte (redirected from natural killer (NK) lymphocyte)

lymphocyte /lym·pho·cyte/ (lim´fo-sit) a mononuclear, nongranular leukocyte having a deeply staining nucleus containing dense chromatin and a pale-blue–staining cytoplasm. Chiefly a product of lymphoid tissue, it participates in immunity.lymphocyt´ic

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B lymphocytes  B cells, bursa-dependent lymphocytes; the precursors of antibody-producing cells (plasma cells) and the cells primarily responsible for humoral immunity.

cytotoxic T lymphocytes  (CTL) differentiated T lymphocytes that can recognize and lyse target cells bearing specific antigens recognized by their antigen receptors; they are important in graft rejection and killing of tumor cells and virus-infected host cells.

Rieder's lymphocyte  a myeloblast sometimes seen in acute leukemia and chronic lymphocytic leukemia, having a nucleus with several wide and deep indentations suggesting lobulation.

T lymphocytes  T cells, thymus-dependent lymphocytes; those that pass through or are influenced by the thymus before migrating to tissues; they are responsible for cell-mediated immunity and delayed hypersensitivity.

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lym·pho·cyte (lmf-st)

n.

Any of the nearly colorless cells formed in lymphoid tissue, as in the lymph nodes, spleen, thymus, and tonsils, constituting between 22 and 28 percent of all white blood cells in the blood of a normal adult human. They function in the development of immunity and include two specific types, B cells and T cells.

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lympho·cytic (-stk) adj.

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Lymphocyte

A type of white blood cell that is important in the formation of antibodies. Doctors can monitor the health of AIDS patients by measuring the number or proportion of certain types of lymphocytes in the patient's blood.

Mentioned in: AIDS, AIDS Tests, Immunosuppressant Drugs, Lymphocytopenia, Severe Combined Immunodeficiency, Sore Throat, Thymoma, Tissue Typing, White Blood Cell Count and Differential

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lymphocyte(s) (lim´fōsīt),

n a form of white blood cell originating in lymphoid tissues; possesses a single spherical nucleus and a nongranular cytoplasm. It constitutes 25% of the white blood cells. Some, along with plasma cells and histiocytes, are found in clinically normal gingivae. Their numbers within the gingival connective tissue are increased in periodontal disease. With progress of gingival inflammation to the underlying bone, they are also found within the marrow spaces of the supporting bone.

lymphocytes-B,

n short-lived, non thymus-dependent lymphocytes that synthesize antibodies for insertion into their own cytoplasmic membranes. They are the precursor of the plasma cells.

lymphocytes, in pulp tissue,

n.pl a subset of white blood cells that, when present, are located near the odontoblastic layer. An increase in lymphocyte count is indicative of inflammation.

lymphocytes-T,

n long-lived lymphocytes that have circulated through the thymus gland and have differentiated to become thymocytes. When exposed to an antigen, they divide rapidly and produce large numbers of new T cells sensitized to that antigen. Some T cells are often called
killer cells, because they secrete immunologically essential chemical compounds and assist B cells in destroying foreign protein. T cells also appear to play a significant role in the body's resistance to the proliferation of cancer cells.

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lymphocyte

a mononuclear, nongranular leukocyte having a deeply staining nucleus containing dense chromatin and a sparse, pale-blue-staining cytoplasm. It participates in immunity.

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activated lymphocyte

one that has reacted on exposure to antigen or to a mitogen.

lymphocyte-activating antigen

see lymphocyte-defined antigen (below).

B l's

thymus-independent lymphocytes, which develop from stem cells in hematopoietic tissue, including the blood islands of the fetal yolk sac, the fetal liver and spleen, and the bone marrow. The B in B lymphocyte refers to the bursa of Fabricius, an organ in birds where B cell differentiation occurs. No analogous organ has been found in mammals, though an equivalent is assumed to exist—probably bone marrow.

B lymphocytes are involved in humoral immunity, i.e. the production of antibodies. A small, mature B lymphocyte can be activated by the binding of an antigen to specific cell-surface receptors. This induces proliferation of the cell, resulting in an expanded clone of cells specific for that antigen. These cells can then differentiate and begin to secrete immunoglobulin (Ig) molecules. Antibody production for most antigens involves interaction with helper T lymphocytes. All of the cells of a single clone secrete Ig that binds specifically to the antigen that stimulated the production of antibody. Mature antibody-secreting cells are plasma cells. Following blastogenesis some of the cells produced by division revert to small lymphocytes and remain as a longlived clone of 'memory' cells.

lymphocyte blastogenesis

increased DNA synthesis followed by cell division and differentiation of lymphocytes in response to antigens or mitogens; an in vitro test of lymphocyte function.

lymphocyte-defined antigen

histocompatibility antigens found on lymphocytes, macrophages, epidermal cells and sperm, capable of stimulating division in allogeneic lymphocytes. Called also lymphocyte-activating antigen.

helper l's

a subset of T lymphocytes that is itself comprised of Th1 and Th2 cells that cooperate with and regulate B lymphocytes in the antibody response and with themselves and other effector T lymphocytes.

histiocytic lymphocyte

see prolymphocyte.

intraepidermal l's

cellular components of the cutaneous immune system.

intraepithelial l's

cellular components of the mucosal immune system.

large lymphocyte

lymphoblast.

large granular lymphocyte

see natural killer cell.

memory lymphocyte

see memory cell.

natural killer (NK) lymphocyte

see natural killer cell.

non-T, non-B lymphocyte

see null cell.

pre-B lymphocyte

a progenitor B cell derived from bone marrow stem cells.

resting lymphocyte

small lymphocytes in the G₀ stage of the cell cycle, prior to activation.

small lymphocyte

unstimulated B and T lymphocytes.

lymphocyte stimulation test

see lymphocyte blastogenesis (above).

suppressor (Ts) lymphocyte

see T lymphocytes (below).

T l's

lymphocytes produced from pluripotential bone marrow stem cells which migrate during late embryogenesis to the thymus. Enormous numbers of cells are produced in the thymus, most of which are destroyed there. Less than 10% of cells which are non-self reactive leave the thymus to populate the T lymphocyte areas of the secondary lymphoid tissues (lymph nodes, spleen, Peyer's patches, etc.). At least four subsets of T lymphocytes are defined by cell surface markers and more especially by function.

Three of the subsets are regulatory cells called T helper (Th) 1 and 2, and T suppressor (Ts) lymphocytes. The other subset is an effector cell called cytotoxic T (Tc) lymphocytes or CTLs. Following antigen binding to antigen-specific T cell receptor (TCR) molecules, T lymphocytes, like B lymphocytes, undergo blastogenesis, in which they enlarge and divide. Some daughter cells revert to form an expanded clone of memory T lymphocytes. For both regulatory and effector functions, T lymphocytes produce a number of substances generally referred to as lymphokines. Lymphokines, unlike antibody, do not bind specifically with antigen, but rather they direct cell functions.

thymus-derived lymphocyte

see T lymphocytes (above).

lymphocyte transfer test

injection of lymphocytes from a potential graft recipient into the skin of a potential donor can be a test of histocompatibility, primarily in humans at the LD loci. Noncompatibility is marked by an inflammatory skin reaction.

lymphocyte transformation test

see lymphocyte blastogenesis (above).

lymphocyte transforming factor (LTF)

an obsolete term for a lymphokine that causes transformation and clonal expansion of nonsensitized lymphocytes.

tumor-infiltrating l's (TILs)

T lymphocyte preparations from surgically removed cancer tissue that may be activated in vitro and returned to the host as a basis for specific anticancer therapy.