Lymphocyte

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Lymphocytes
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Lymphocyte
A scanning electron microscope (SEM) image of a single human lymphocyte
Details
SystemImmune system
FunctionWhite blood cell
Identifiers
MeSHD008214
THH2.00.04.1.02002
FMA84065 62863, 84065
Anatomical terms of microanatomy

A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates.[1] Lymphocytes include T cells (for cell-mediated and cytotoxic adaptive immunity), B cells (for humoral, antibody-driven adaptive immunity),[2][3] and innate lymphoid cells (ILCs; "innate T cell-like" cells involved in mucosal immunity and homeostasis), of which natural killer cells are an important subtype (which functions in cell-mediated, cytotoxic innate immunity). They are the main type of cell found in lymph, which prompted the name "lymphocyte" (with cyte meaning cell).[4] Lymphocytes make up between 18% and 42% of circulating white blood cells.[2]

Types

light microscope
4D live imaging of T cell nuclear dynamics viewed using holotomography microscopy
Giemsa stained lymphocytes in peripheral blood

The three major types of lymphocyte are T cells, B cells and natural killer (NK) cells.[2] Lymphocytes can be identified by their large nucleus.

T cells and B cells

Main articles: T cell and B cell

T cells (

immunity
.

Natural killer cells

Main article: Natural killer cell

NK cells are a part of the

cytotoxic (cell-killing) granules which then destroy the altered cells.[1]
They are named "natural killer cells" because they do not require prior activation in order to kill cells which are missing MHC class I.

Dual expresser lymphocyte – X cell

The X lymphocyte is a reported cell type expressing both a B-cell receptor and T-cell receptor and is hypothesized to be implicated in type 1 diabetes.[6][7] Its existence as a cell type has been challenged by two studies.[8][9] However, the authors of original article pointed to the fact that the two studies have detected X cells by imaging microscopy and FACS as described.[10] Additional studies are required to determine the nature and properties of X cells (also called dual expressers).

Development

Development of blood cells

Mammalian

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

Memory T cells remain in the peripheral tissues and circulation for an extended time ready to respond to the same antigen upon future exposure; they live weeks to several years, which is very long compared to other leukocytes.[citation needed
]

Characteristics

A scanning electron microscope image of normal circulating human blood showing red blood cells, several types of white blood cells including lymphocytes, a monocyte, a neutrophil and many small disc-shaped platelets

Microscopically, in a

immunoglobulins
by these cells.

It is impossible to distinguish between T cells and B cells in a peripheral blood smear.

ELISPOT or secretion assay techniques can be used.[1]

Typical recognition markers for lymphocytes[14]
Class Function Proportion (median, 95% CI) Phenotypic marker(s)
Natural killer cells Lysis of virally infected cells and tumour cells 7% (2–13%)
CD56 but not CD3
T helper cells Release cytokines and growth factors that regulate other immune cells 46% (28–59%)
TCRαβ, CD3 and CD4
Cytotoxic T cells Lysis of virally infected cells, tumour cells and allografts 19% (13–32%)
TCRαβ, CD3 and CD8
Gamma delta T cells Immunoregulation and cytotoxicity 5% (2–8%)
TCRγδ and CD3
B cells Secretion of antibodies 23% (18–47%) MHC class II, CD19 and CD20

In the

macrophages
, which are rather stationary in the nodes.

Lymphocytes and disease

Several lymphocytes seen collected around a tuberculous granuloma

A lymphocyte count is usually part of a peripheral

complete blood cell count
and is expressed as the percentage of lymphocytes to the total number of white blood cells counted.

A general increase in the number of lymphocytes is known as lymphocytosis,[16] whereas a decrease is known as lymphocytopenia.

High

An increase in lymphocyte concentration is usually a sign of a

μl
in adults or over 8000 per μl in children. This is unique in that many bacterial infections illustrate neutrophil-predominance instead.

Lymphoproliferative disorders

Lymphoproliferative disorders (LPD) encompass a diverse group of diseases marked by uncontrolled lymphocyte production, leading to issues like lymphocytosis, lymphadenopathy, and bone marrow infiltration. These disorders are common in immunocompromised individuals and involve abnormal proliferation of T and B cells, often resulting in immunodeficiency and immune system dysfunction. Various gene mutations, both iatrogenic and acquired, are implicated in LPD. One subtype, X-linked LPD, is linked to mutations in the X chromosome, predisposing individuals to natural killer cell LPD and T-cell LPD. Additionally, conditions like common variable immunodeficiency (CVID), severe combined immunodeficiency (SCID), and certain viral infections elevate the risk of LPD. Treatment methods, such as immunosuppressive drugs and tissue transplantation, can also increase susceptibility. LPDs encompass a wide array of disorders involving B-cell (e.g., chronic lymphocytic leukemia) and T-cell (e.g., Sezary syndrome) abnormalities, each presenting distinct challenges in diagnosis and management.[18]

Low

A low normal to low absolute lymphocyte concentration is associated with increased rates of infection after surgery or trauma.[19]

One basis for low T cell lymphocytes occurs when the

acquired immune deficiency syndrome (AIDS). The effects of other viruses or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in the blood
.

Tumor-infiltrating lymphocytes

Main article:
Tumor-infiltrating lymphocyte

In some cancers, such as

tumor
. This can sometimes lead to regression of the primary tumor.

Lymphocyte-variant hypereosinophilia

Main article: Lymphocyte-variant hypereosinophilia

Blood content

Reference ranges for blood tests of white blood cells, comparing lymphocyte amount (shown in light blue) with other cells

History

Main article: Lymphocyte T-cell immunomodulator § History

See also

Notes

  1. ^ The process of B-cell maturation was elucidated in birds and the B most likely means "bursa-derived" referring to the bursa of Fabricius.[5] However, in humans (who do not have that organ), the bone marrow makes B cells, and the B can serve as a reminder of bone marrow.

References

  1. ^
    ISBN 0-8153-4101-6
    .
  2. ^
    ISBN 978-0-323-53045-3
    .
  3. ^
    ISBN 9780323085939
    . Retrieved 22 July 2020.
  4. ^ "NCI Dictionary of Cancer Terms". National Cancer Institute. Retrieved 22 July 2020. A type of immune cell that is made in the bone marrow and is found in the blood and in lymph tissue. The two main types of lymphocytes are B lymphocytes and T lymphocytes. B lymphocytes make antibodies, and T lymphocytes help kill tumor cells and help control immune responses. A lymphocyte is a type of white blood cell.
  5. ^ "B Cell". Merriam-Webster Dictionary. Encyclopaedia Britannica. Retrieved 28 October 2011.
  6. PMID 31150624
    .
  7. ^ "Newly Discovered Immune Cell Linked to Type 1 Diabetes". Johns Hopkins Medicine Newsroom. 30 May 2019. Retrieved 9 August 2020.
  8. S2CID 231809927
    .
  9. PMID 32400942
    .
  10. PMID 33545037
    .
  11. ^
    ISBN 0-7216-0008-5
    .
  12. PMID 35265979
    .
  13. ^
    PMID 25656707
    .
  14. PMID 15807853
    .
  15. S2CID 241913878
    .
  16. ^ a b "Lymphocytosis: Symptoms, Causes, Treatments". Cleveland Clinic. Retrieved 22 July 2020.
  17. S2CID 78707217
    . Lymphocytes are recruited into the upper and lower airways during the early stages of a viral respiratory infection, and it is presumed that these cells help to limit the extent of infection and to clear virus-infected epithelial cells.
  18. PMID 30725847
    , retrieved 7 October 2023
  19. S2CID 78729807
    . Retrieved 5 January 2021.
  20. S2CID 241056897
    . Lymphocytopenia may also be acquired, for example, in patients with HIV infection.

External links

Wikimedia Commons has media related to Lymphocytes.
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