T Cells

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton and Vidya Acharya  

Introduction[edit | edit source]

Healthy Human T Cell

T lymphocytes are a critical part of the adaptive immune system safeguarding against infection and malignancy, but also implicated in many immune pathologies.[1] T cells arise from bone marrow and mature in the thymus. The thymus is a lymphatic system gland that functions principally to support the development of mature T cells (the "T " in T cell lymphocyte stands thymus derived).

  • T-cells work with macrophages, however unlike macrophages that can attack any invading cell or virus, each T-cell can fight only one type of virus.
  • T cell lymphocytes are different from B cell lymphocytes and natural killer cells in that they have a protein called a T-cell receptor on their cell membrane.

Watch the 6 minute video below titled "Immune Response Explained: T-Cell Activation"

[2]

Types of T Cells[edit | edit source]

Immune response.png

There are various types of T cells namely:

  • Naive T cell: T cell that has matured and been released by the thymus but has not yet encountered its corresponding antigen, that is they are in the stage between maturity and activation. Each naïve T cell has a unique T cell receptor that recognizes a specific antigen, and once they encounter their antigen specific the activation of naïve T cells will begin.[3]
  • CD8+ T Cells (cytotoxic T cells, or killer T cells): actively destroy infected cells through the use of granule sacs that contain digestive enzymes, thus killing the infected cells.
  • CD4+ T cells (helper T cells): coordinate the immune attack by activating cytotoxic T cells, macrophages, and stimulating antibody production by B cell lymphocytes. A CD4 count is used to check the health of the immune system in people infected with HIV (human immunodeficiency virus). HIV attacks and destroys CD4 cells[4].
  • Regulatory T cells (also called Tregs): suppress the actions of B and T cells to decrease the immune response when a highly active response is no longer warranted. Tregs control the immune response to self and foreign particles (antigens) and help prevent autoimmune disease.[5]
  • Natural Killer T cells: distinguish infected or cancerous cells from normal body cells and attack cells that do not contain molecular markers that identify them as body cells.
  • Memory T cells: protect against previously encountered antigens and may provide lifetime protection against some pathogens[6].

Major Histocompatibility Complex’s (MHC) Role[edit | edit source]

Antigen presentation to T cell

T cells cannot recognize soluble, free antigens, they can only recognize protein-based, receptor-bound antigens. This recognition occurs via the use of the MHC also known as HLA(human leucocyte antigen) 1 and 2 receptors, which along with the T-cell receptors bind the antigen it seeks and form a complex that allows the T cell to remember the antigen. The T-cell receptor is a protein complex found on the surface of T cells that is responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules, and are not found on B cells.[1]

Lymphocyte activation, APC antigen presenting molecule.

MHC molecules are important components of the immune system, allowing T lymphocytes to detect cells, for example macrophages, that have ingested infectious microorganisms. The macrophage engulfs a microorganism and partially digests it and displays peptide fragments of the microbe on its surface, bound to MHC molecules. The T lymphocyte identifies the foreign fragment attached to the MHC molecule and binds to it, arousing an immune response. In uninfected healthy cells, the MHC molecule presents peptides from its own cell (self peptides), to which T cells do not normally react.[7]

From Lymphatic to Circulatory System[edit | edit source]

Lymph capillary.png

T cells, like most lymphocytes are stored in the lymph system until they are required to fight an infection. When a virus invades, the lymphocytes can move into the blood vessels so they can quickly attack the viruses. This transfer happens in the lymph nodes, which are located throughout the body. In these nodes the T-cells and B-cells multiply and get ready to attack the virus. Other important parts of the lymph system where immune cells grow, multiply, and catch invaders are your bone marrow, thymus, spleen, and tonsils[8].

Immunosenescence[edit | edit source]

With aging the acquired immune function shows distinct changes, termed immunosenescence. These changes include T-cell dysfunction, which may cause this diminished resistance to infection and increased prevalence of chronic age-associated diseases in older persons. T-cell dysfunction occurs at many stages, from naive cells to the end stages of differentiation during immune responses. The thymus, which generates naive T cells, shows involution resulting in progressive reduction of T-cell output after adolescence, however peripheral T-cell numbers are preserved.[9]See image below re immune cell changes with immunosenescence.

Changes in immune cells during immunosenescence

Physiotherapy Implications[edit | edit source]

Cycling has immune function benefits
Immune boosting foods list.png

Exercise is proving to be a very beneficial medicine at all ages. Below are a few examples of the effect exercise has on T cells and the immune response.

  • Regular exercise can increase T-cells, enhance vaccination response, and boost the function of the natural killer cells in the immune system.[10]
  • The impaired effector function of fatigued and senescent T cells is involved in cancer progression and inadequate vaccine responses. Repeated exercise was shown to be beneficial through limiting the accumulation of senescent and exhausted CD8+ T cells (killer T cells). This probably relates to exercise-induced preferential mobilization of senescent T cells encouraging apoptosis in the peripheral circulating blood.[11]
  • Data from animal studies demonstrate that CD8+ T (killer T cells) cells are metabolically altered by exercise in a manner that acts to improve their antitumoral efficacy[12].
  • In the older sedentary people, the output of new T cells from the thymus glands is low. The inactive older peoples’ results differed from those of a group of older cyclists, who had almost as many new T cells in their blood as did the young people[13].

Diet can also influence the immune system. Education re diet, and immune boosting food can be useful to specific populations eg the aged and immunocomprimised clients.

References[edit | edit source]

  1. 1.0 1.1 Dimeloe S, Burgener AV, Grählert J, Hess C. T‐cell metabolism governing activation, proliferation and differentiation; a modular view. Immunology. 2017 Jan;150(1):35-44. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5341500/(accessed 3.8.2022)
  2. Demystifying Medicine McMaster. Immune Response Explained: T-Cell Activation. Available from: https://www.youtube.com/watch?app=desktop&v=6eMh0Vpyoik [last accessed 6.8.2022]
  3. Akedeum Naive T cells Available: https://www.akadeum.com/blog/what-are-naive-cells/ (accessed 3.8.2022)
  4. Midline plus CD4+ Lymphocyte count Available: https://medlineplus.gov/lab-tests/cd4-lymphocyte-count/ (accessed 3.8.2022)
  5. BS of immunology T regulatory cells (Trega) Available: https://www.immunology.org/public-information/bitesized-immunology/cells/regulatory-t-cells-tregs ( accessed 3.8.2022)
  6. Thought Co Available T cells:https://www.thoughtco.com/t-cells-meaning-373354 (accessed 3.8.2022)
  7. Britannica MHC Available:https://www.britannica.com/science/major-histocompatibility-complex (accessed 3.8.2022)
  8. Ask a biologist T cell Available:https://askabiologist.asu.edu/t-cell (accessed 4.8.2022)
  9. Minato N, Hattori M, Hamazaki Y. Physiology and pathology of T-cell aging. International immunology. 2020 Apr;32(4):223-31.Available:https://academic.oup.com/intimm/article/32/4/223/5713759?login=false (accessed 4.8.2022)
  10. Sander R. Exercise boosts immune response. Nursing older people. 2012 Jun 1;24(6):11-. Available:https://pubmed.ncbi.nlm.nih.gov/27750511/ (ACCESSED 4.8.2022)
  11. Donovan T, Bain AL, Tu W, Pyne DB, Rao S. Influence of Exercise on Exhausted and Senescent T Cells: A Systematic Review. Frontiers in Physiology. 2021:1331. Available:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8417807/ (accessed 4.8.2022)
  12. Rundqvist H, Veliça P, Barbieri L, Gameiro PA, Bargiela D, Gojkovic M, Mijwel S, Reitzner SM, Wulliman D, Ahlstedt E, Ule J. Cytotoxic T-cells mediate exercise-induced reductions in tumor growth. Elife. 2020 Oct 23;9:e59996. Available:https://pubmed.ncbi.nlm.nih.gov/33095157/ (accessed 4.8.2022)
  13. Duggal NA, Pollock RD, Lazarus NR, Harridge S, Lord JM. Major features of immunesenescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood. Aging cell. 2018 Apr;17(2):e12750. Available:https://pubmed.ncbi.nlm.nih.gov/29517845/ (accessed 2.8.2022)