11.5B: Development of the Dual Lymphocyte System

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    Learning Objectives
    • Examine dual lymphocyte development

    The cells of the adaptive immune system are a type of leukocyte, called a lymphocyte. The human body has about 2 trillion lymphocytes, constituting 20-40% of white blood cells (WBCs); their total mass is about the same as the brain or liver. The peripheral blood contains 20–50% of circulating lymphocytes; the rest move within the lymphatic system. B cells and T cells are the major types of lymphocytes.

    B Cell and T Cell Differentiation

    Mammalian stem cells differentiate into several kinds of blood cell within the bone marrow. This process is called haematopoiesis. During this process, all lymphocytes originate from a common lymphoid progenitor before differentiating into their distinct lymphocyte types. The differentiation of lymphocytes into distinguishable types follows various pathways in a hierarchical fashion as well as in a more plastic fashion. The formation of lymphocytes is known as lymphopoiesis. B cells mature into B lymphocytes in the bone marrow, while T cells migrate to, and mature in, a distinct organ called the thymus. Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen and lymph nodes) where they survey for invading pathogens and/or tumor cells.

    image
    Figure: Hematopoeisis in humans: 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.

    Further Differentiation

    The lymphocytes involved in adaptive immunity (i.e. B and T cells) differentiate further after exposure to an antigen; they form effector and memory lymphocytes. Effector lymphocytes function to eliminate the antigen, either by releasing antibodies (in the case of B cells), cytotoxic granules (cytotoxic T cells) or by signaling to other cells of the immune system (helper T cells). Memory cells remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure.

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    • Robert Bear and David Rintoul, Adaptive Immunity. December 11, 2013. Provided by: OpenStax CNX. Located at: http://cnx.org/content/m47434/latest/. License: CC BY: Attribution
    • OpenStax College, Biology. October 17, 2013. Provided by: OpenStax CNX. Located at: http://cnx.org/content/m44821/latest...ol11448/latest. License: CC BY: Attribution
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    • antibody. Provided by: Wiktionary. Located at: en.wiktionary.org/wiki/antibody. License: CC BY-SA: Attribution-ShareAlike
    • Robert Bear and David Rintoul, Adaptive Immunity. December 11, 2013. Provided by: OpenStax CNX. Located at: http://cnx.org/content/m47434/latest/. License: CC BY: Attribution
    • Robert Bear and David Rintoul, Adaptive Immunity. December 11, 2013. Provided by: OpenStax CNX. Located at: http://cnx.org/content/m47434/latest/. License: CC BY: Attribution
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    • Robert Bear and David Rintoul, Adaptive Immunity. December 11, 2013. Provided by: OpenStax CNX. Located at: http://cnx.org/content/m47434/latest/. License: CC BY: Attribution
    • Robert Bear and David Rintoul, Adaptive Immunity. December 11, 2013. Provided by: OpenStax CNX. Located at: http://cnx.org/content/m47434/latest/. License: CC BY: Attribution
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    Key Points

    • B cells and T cells are the major types of lymphocytes.
    • B cells mature into B lymphocytes in the bone marrow, while T cells migrate to, and mature in, a distinct organ called the thymus.
    • Following maturation, the lymphocytes enter the circulation and peripheral lymphoid organs (e.g. the spleen and lymph nodes) where they survey for invading pathogens and/or tumor cells.
    • The lymphocytes involved in adaptive immunity (i.e. B and T cells) differentiate further after exposure to an antigen to form effector and memory lymphocytes.

    Key Terms

    • lymphocyte: A type of white blood cell or leukocyte that is divided into two principal groups and a null group: B-lymphocytes, which produce antibodies in the humoral immune response, T-lymphocytes, which participate in the cell-mediated immune response, and the null group, which contains natural killer cells, cytotoxic cells that participate in the innate immune response.
    • leukocyte: A white blood cell.
    • haematopoiesis: Hematopoeisis is the formation of blood cellular components from a common progenitor stem cell.

    11.5B: Development of the Dual Lymphocyte System is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.