Helper T cell
Say it: HEL-per TEE sel
A helper T cell is a CD4 T lymphocyte that coordinates immune responses, releasing cytokines that activate B cells, killer T cells and macrophages.
Also: T helper cell, CD4+ T cell, Th cell, CD4 cell
Definition
What is a helper T cell?
Helper T cells, also called CD4+ T cells, are T lymphocytes whose main job is to direct other immune cells rather than attack invaders themselves. Each recognizes one specific antigen fragment presented on MHC class II molecules, which are carried by antigen-presenting cells such as dendritic cells, macrophages and B cells. The CD4 coreceptor binds the MHC molecule and helps hold the two cells together.
Once activated, a helper T cell multiplies and releases cytokines, signaling proteins that shape the whole response. Different subsets suit different threats. Th1 cells, which make interferon-gamma, activate macrophages and support cytotoxic T cells against microbes that live inside cells. Th2 cells, which make interleukins such as IL-4, help B cells become antibody-secreting plasma cells and are geared to invaders outside cells. Other subsets include Th17 and follicular helper cells, while related regulatory T cells keep responses in check.
Because helper T cells support both antibody and cell-mediated immunity, losing them is devastating. HIV enters cells through CD4, and as helper T cell numbers fall, the body can no longer fight off opportunistic infections, the stage called AIDS.
Related
Terms that go with it
- T cellA T cell is a white blood cell that matures in the thymus and drives cell-based immunity, directing other immune cells or killing infected cells.
- B cellA B cell is a lymphocyte, a kind of white blood cell, that produces antibodies and forms a key part of the adaptive immune system.
- Cytotoxic T cellA cytotoxic T cell is a white blood cell of adaptive immunity that finds and kills body cells infected by viruses or turned cancerous.
- CytokineA cytokine is a small signaling protein released by cells, especially immune cells, that changes how other cells behave, grow or respond to infection.
- MacrophageA macrophage is a large white blood cell that engulfs and digests microbes, dead cells and debris, and signals other immune cells to act.
- Major histocompatibility complexThe major histocompatibility complex is a set of genes whose proteins display protein fragments on cell surfaces so that T cells can inspect them.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- NCI Dictionary of Cancer Terms: helper T cell
- OpenStax Anatomy and Physiology 2e, 21.3 The Adaptive Immune Response: T Lymphocytes and Their Functional Types
- OpenStax Anatomy and Physiology 2e, 21.6 Diseases Associated with Depressed or Overactive Immune Responses
- Crater et al., A History and Atlas of the Human CD4+ T Helper Cell, Biomedicines (2023)
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