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Lymphocyte
Lymphocytes are a category of white blood cells and play important roles in both the innate and adaptive immune system.[1] Lymphocytes include natural killer cells, T cells, and B cells.[2] Lymphocytes circulate throughout the body via lymphatic fluid, also known as lymph, as part of the lymphatic system.[3] Lymph circulates between blood, tissues, and lymph nodes, transporting immature lymphocytes for maturation, relocation of mature lymphocytes during immune surveillance, or distribute activated lymphocytes to respond to pathogens. Lymph nodes act as filters for lymph fluid and house populations of mature lymphocytes. Lymphocytes make up 40% of the immune cell population.[4]
Lymphocytes differentiate from a stem cell progenitor known as the common lymphoid progenitor in the bone marrow. B cells develop and mature in the bone marrow, while T cells mature in the thymus. During their maturation, both cell types undergo positive and negative selection of their surface B cell and T cell receptors for their respective cell types to ensure proper functionality while also removing cells with "self"-recognition, i.e., the ability to activate in response to the body itself. Positive selection checks if cells can activate in response to threats while negative selection removes autoreactive cells. Mature B and T cells reside in lymph nodes and await presentation of an antigen before activating as part of the adaptive immune system.
Natural killer (NK) cells are cytotoxic lymphocytes of the innate immune system and do not require activation prior to their cytotoxic behavior. Instead, they recognize missing major histocompatibility complex (MHC) class I surface proteins and other receptors to identify tumor cells or cells infected by viruses.[5] Receptors on NK cells are both activating and inhibiting cytotoxicity: receptors binding to MHC I suppress activation, while receptors binding to stress-associated molecules pushes NK cells towards activation. This mechanism not only allows NK cells to respond rapidly, but also target damaged cells evading "killer" T cells by suppressing MHC I expression. Activated NK cells release cytokines to signal further immune involvement, such as interferon-γ, tumor necrosis factor-α, Interleukin (IL)-5, IL-10, IL-13.[5] These cells also play a role in clearing senescent cells.
See also
- B cells
- T cells
- Natural killer cell
- Leucocytes (white blood cells)
- Red blood cells
- Innate Immune System
- Adaptive Immune System
Learn more
Leucocytes and platelets - OpenStax Innate Immunity - OpenStax
References
- ↑ Male, D. (2010). Immunology. 7th ed. [Philadelphia, Pa.]: Mosby Elsevier.
- ↑ "12.2 Innate Immunity – Concepts of Biology-1st Canadian Edition". opentextbc.ca. Retrieved October 8, 2018.
- ↑ Young, Alan J. (1999-04). "The physiology of lymphocyte migration through the single lymph node in vivo". Seminars in Immunology. 11 (2): 73–83. doi:10.1006/smim.1999.0163. ISSN 1044-5323. Check date values in:
|date=(help) - ↑ R. Sender, Y. Weiss, Y. Navon, I. Milo, N. Azulay, L. Keren, S. Fuchs, D. Ben-Zvi, E. Noor, & R. Milo, The total mass, number, and distribution of immune cells in the human body, Proc. Natl. Acad. Sci. U.S.A. 120 (44) e2308511120, https://doi.org/10.1073/pnas.2308511120 (2023).
- ↑ 5.0 5.1 Paul S, Lal G. The Molecular Mechanism of Natural Killer Cells Function and Its Importance in Cancer Immunotherapy. Front Immunol. 2017 Sep 13;8:1124. doi: 10.3389/fimmu.2017.01124. PMID: 28955340; PMCID: PMC5601256.
