lymphocyte

(noun)

a type of white blood cell or leukocyte that is divided into two principal groups and a null group: B-cells, T-cells, and natural killer (NK) cells

Related Terms

Examples of lymphocyte in the following topics:

  • Cytotoxic T Lymphocytes and Mucosal Surfaces

    • Approximately 0.1 percent of all cells in the blood are leukocytes, which include monocytes (the precursor of macrophages) and lymphocytes.
    • On maturation, T and B lymphocytes circulate to various destinations.
    • Antigen-presenting cells (APCs) in the lymph nodes capture and process antigens, informing nearby lymphocytes about potential pathogens.
    • The spleen is also the site where APCs that have trapped foreign particles in the blood can communicate with lymphocytes.
    • Lymph nodes are filled with lymphocytes that purge infecting cells.

  • Natural Killer Cells

    • Lymphocytes are leukocytes (white blood cells) that are histologically identifiable by their large, darkly-staining nuclei; they are small cells with very little cytoplasm .
    • After a pathogen enters the body, infected cells are identified and destroyed by natural killer (NK) cells, which are a type of lymphocyte that can kill cells infected with viruses or tumor cells (abnormal cells that uncontrollably divide and invade other tissue).
    • While NK cells are part of the innate immune response, they are best understood relative to their counterparts in the adaptive immune response,T cells, which are also classified as lymphocytes.
    • T cells are lymphocytes that mature in the thymus gland and identify intracellular infections, especially from viruses, by the altered expression of major histocompatibility class (MHC) I molecules on the surface of infected cells.
    • Lymphocytes, such as NK cells, are characterized by their large nuclei that actively absorb Wright stain and, therefore, appear dark colored under a microscope.

  • Cell-Mediated Immunity

    • Unlike B cells, T lymphocytes (T cells) are unable to recognize pathogens without assistance.
    • There are two main types of T cells: helper T lymphocytes (TH) and the cytotoxic T lymphocytes (TC).
    • The TH lymphocytes function indirectly to tell other immune cells about potential pathogens, while cytotoxic T cells (TC) are the key component of the cell-mediated part of the adaptive immune system which attacks and destroys infected cells.
    • TC cells also support NK lymphocytes to destroy early cancers.
    • Lymphocytes of the adaptive immune response must interact with antigen-embedded MHC class II molecules to mature into functional immune cells.

  • White Blood Cells

    • The second main group is the agranulocytes, which lack granules in their cytoplasm, and include the monocytes and lymphocytes ( b).
    • Lymphocytes are the primary cells of the immune system.
    • (b) Agranulocytes include lymphocytes and monocytes.
    • Lymphocytes, including B and T cells, are responsible for adaptive immune response.

  • Immunodeficiency

    • For instance, radiation exposure can destroy populations of lymphocytes, elevating an individual's susceptibility to infections and cancer.
    • Dozens of genetic disorders result in immunodeficiencies, including Severe Combined Immunodeficiency (SCID), bare lymphocyte syndrome, and MHC II deficiencies.
    • Image of HIV: scanning electron micrograph of HIV-1 budding (in green, color added) from cultured lymphocyte

  • Antigen-presenting Cells: B and T cells

    • Lymphocytes, which are white blood cells, are formed with other blood cells in the red bone marrow found in many flat bones, such as the shoulder or pelvic bones.
    • The two types of lymphocytes of the adaptive immune response are B and T cells .
    • Whether an immature lymphocyte becomes a B cell or T cell depends on where in the body it matures.
    • This scanning electron micrograph shows a T lymphocyte.

  • Regulating Immune Tolerance

    • The primary mechanism for developing immune tolerance to self-antigens occurs during the selection for weakly, self-binding cells during T and B lymphocyte maturation.
    • Any T or B lymphocytes that recognize harmless foreign or "self" antigens are deleted before they can fully mature into immunocompetent cells.
    • Immune tolerance is brought about by specialized APCs in the liver, lymph nodes, small intestine, and lung that present harmless antigens to a diverse population of regulatory T (Treg) cells: specialized lymphocytes that suppress local inflammation and inhibit the secretion of stimulatory immune factors.

  • The Role of Blood in the Body

    • White blood cells (including neutrophils, monocytes, lymphocytes, eosinophils, and basophils) are involved in the immune response.

  • Immunological Memory

    • A memory cell is an antigen-specific B or T lymphocyte that does not differentiate into an effector cell during the primary immune response, but that can immediately become an effector cell on re-exposure to the same pathogen.

  • Connective Tissues: Loose, Fibrous, and Cartilage

    • Macrophages, lymphocytes, and, occasionally, leukocytes can be found in some of the tissues, while others may have specialized cells.