T Cells: Types and Function (2023)


What are T-cells (T lymphocytes)?

T-cells are a type of white blood cell called lymphocytes. They’re also called T lymphocytes. Lymphocytes play an essential role in your immune system. Your immune system fights infection-causing pathogens (viruses, bacteria, fungi and parasites) and harmful cells, like cancer cells.

Your lymphocytes include T-cells and B-cells. Both types are part of your body’s defense. B-cells make proteins called antibodies to fight pathogens. T-cells protect you by destroying harmful pathogens and by sending signals that help control your immune system’s response to threats.

What are the different types of T-cells?

There are two main types of T-cells:

  • Cytotoxic T-cells: Cytotoxic T-cells are also called CD8+ cells because they have a CD8 receptor on their membranes. These cells get their name from “cyto,” which means cell, and “toxic,” which means poisonous or harmful. Cytotoxic T-cells kill cells infected with viruses and bacteria, and they also destroy tumor cells.
  • Helper T-cells: Helper T-cells are also called CD4+ cells because they have a CD4 receptor on their membranes. Unlike cytotoxic T-cells, helper T-cells don’t kill cells directly. Instead, they send signals that tell other cells in your immune system how to coordinate an attack against invaders. Helper T-cells signal cytotoxic T-cells, B-cells and another type of white blood cell called a macrophage.

Although they’re not considered one of the main T-cell types, regulatory T-cells (suppressor cells) play an essential role in your immune system. These cells reduce the activity of other T-cells when necessary. They can prevent T-cells from attacking your body’s healthy cells.


What do T-cells do?

T-cells are key fighters in what’s known as your adaptive immune system. Think of your adaptive immune system as a specialized smart system that’s constantly monitoring for threats. Once it detects an intruder, your adaptive immune system builds a customized defense to fight it.

Each T-cell is unique in that it’s designed to fight only one type of intruder. Once your immune system identifies the threat, it locates the specific T-cell designed to defeat it and recruits that T-cell for battle. The T-cell copies itself, making more T-cells to defeat the intruder. These T-cells that join the fight are called effector cells. When your immune system is working properly, these effector T-cells destroy the threat, helping rid you of infection and disease.

Your T-cells continue to protect you even after the intruder’s gone. Some of your T-cells become memory cells instead of effector cells. Unlike effector T-cells, memory T-cells aren’t fighters. Instead, they remember the intruder so that if it returns, your immune system recognizes it and quickly mounts a defense.

How do T-cells work in the immune system?

T-cells work once they’re activated. Several steps have to happen before a T-cell activation:

  1. A cell called an antigen-presenting cell (APC) locates evidence of the intruder and attaches it to a structure called major histocompatibility complex (MHC). This step is important because T-cells can’t recognize evidence of an intruder unless it’s attached to MHC.
  2. The T-cell binds to the MHC. There are two types of MHC. One fits each type of T-cell. The CD8 receptor on a cytotoxic T-cell can only bind to MHC-1. The CD4 receptor on a helper T-cell can only bind to MHC-II.
  3. Once the T-cell binds with all the matching parts, it activates. The binding is important because it ensures that the T-cell is the right one to fight the intruder.

An activated cytotoxic T-cell kills infected cells or cancer cells. An activated helper T-cell sends signals that tell other immune cells what actions to take to fight the intruder.

(Video) T Cell Types and Their Functions


Where are T-cells located?

T-cells exist in different places depending on the point in the cell cycle. T-cells start in your bone marrow, mature in your thymus and eventually relocate to your lymph tissue or bloodstream.

  1. Bone marrow: T-cells start in the spongy tissue inside your bone called marrow. Like all blood cells, they start as hematopoietic stem cells. These cells have the potential to develop into any type of blood cell.
  2. Thymus: T-cells move to an organ called your thymus (located in your upper mid-chest) to mature. At this stage, the immature T-cells are called thymocytes. Your thymus is like boot camp for T-cells. Once inside, T-cells go through testing to be sure they can bind correctly to MHC and won’t attack your body’s healthy cells. They also receive the right receptor, either CD4 (helper T-cells) or CD 8 (cytotoxic T-cells). Only T-cells that pass all these tests go out into your body.
  3. Lymph tissue and bloodstream: Fully mature T-cells travel to tissue and organs in your lymph system, like your spleen, tonsils and lymph nodes. They may also circulate in your bloodstream. T-cells remain on standby in your body until you need them to protect you.

Your thymus is much larger when you’re a child and gets smaller as you age. Related, your thymus starts releasing significantly fewer T-cells starting at around age 20. Your supply of diverse T-cells depends more on your body’s ability to make copies of the T-cells you already have.

(Video) Immunology | T- Cell Development

Conditions and Disorders

What are the common conditions and disorders that affect T-cells?

Several types of autoimmune diseases and immunodeficiency disorders can affect your T-cells. With autoimmune diseases, your immune system malfunctions and attacks your healthy cells. Immunodeficiency disorders may be inherited or acquired, but they involve having a weakened immune system.

Conditions that can affect your T-cells include:

  • Acute lymphocytic leukemia: A type of cancer that starts in your blood and bone marrow.
  • Adult Hodgkin lymphoma: A group of blood cancers that start in your lymphatic system.
  • T-cell lymphomas: A group of blood cancers that start in your T-cells and can affect different tissues, most commonly your skin, but also your lymph nodes and subcutaneous tissue.
  • Chronic T-cell leukemia (T-cell prolymphocytic leukemia): A blood cancer that starts in your T-cells that can affect your bone marrow, blood and lymph nodes.
  • DiGeorge syndrome: A genetic disorder that can prevent your body from making enough healthy T-cells.
  • HIV: A virus that attacks your white blood cells (especially your CD4+ T-cells) and potentially leads to AIDS.
  • Job syndrome: A rare immune system disorder that causes repeat infections.
  • Severe combined immunodeficiency (SCID): A group of rare genetic disorders that involves a weakened immune system resulting from problems with T-cells and other lymphocytes.
  • Thymic aplasia: A condition in which you’re born with an underdeveloped thymus.
  • Wiskott-Aldrich syndrome: A rare genetic condition that involves immune system issues, including atypical white blood cells.

What is the normal range of T-cells?

What’s considered a normal range for T-cells can vary depending on the lab that’s counting your T-cells. Generally, a CD4 count (helper T-cells) that’s between 500 to 1,200 cells/mm3 is considered normal if you’re a healthy adult. A CD8 count (cytotoxic T-cells) between 150 to 1,000 cells per cubic millimeter is considered normal.


Your healthcare provider can explain what a normal result looks like for you depending on your condition and general health.

What does it mean if your T-cells are low?

Low T-cells can signal a range of problems affecting your immune system. Low T-cells may be a sign of a condition that you’re born with that prevents your body from making enough T-cells. Your body may make fewer T-cells in response to a condition you acquire, like HIV. Or low T-cells may be a side effect of certain treatments or medications.

Regardless, not having enough T-cells makes it harder for your body to protect you from your body’s invaders. Having too few T-cells can even be life-threatening.

What does it mean if your T-cells are high?

It’s much less common to have too many T-cells. High T-cells may mean that your body has ramped up production of T-cells to fight an infection. High T-cells may also be a sign of certain cancers.

What are the common tests to check the health of my T-cells?

Your provider may order a T-cell count (also called a CD4 count) if they suspect there’s an issue with your immune system. Or they may order another test called a CD4 to CD8 ratio T-cell test to see how many helper T-cells you have in relation to cytotoxic T-cells.

T-cell counts are especially useful if you’re HIV-positive. They allow your healthcare provider to monitor your immune system’s health and gauge how your treatment’s working.

(Video) T cell differentiation (role of cytokines in T cell differentiation)


How can I boost my T-cells?

Ask your healthcare provider about medications and therapies that can boost your T-cells. In the meantime, you can take steps to benefit your immune system. Sometimes, the best way to protect your T-cells is to prevent yourself from having to rely too much on them. This means steering clear of germs and taking care of yourself.

You can:

  • Eat a well-balanced diet.
  • Stay up-to-date on all vaccines.
  • Avoid alcohol, or drink it in moderation.
  • Don’t smoke or vape and quit if you do.
  • Sleep at least seven to eight hours each night.
  • Engage in moderate exercise for at least 150 minutes a week.
  • Wear a mask in indoor areas, especially areas with poor ventilation.
  • Wash your hands frequently with soap and water or use hand sanitizer.

Frequently Asked Questions

What is the difference between T-cells and antibodies?

Both T-cells and antibodies protect you from pathogens, but they play different roles in your immune system. B-cells are the other type of white blood cell (lymphocytes). It’s B-cells (not T-cells) that make antibodies, a specific type of protein that kills harmful invaders. While B-cells send antibodies to kill harmful cells, cytotoxic T-cells kill harmful cells directly.

A note from Cleveland Clinic

(Video) Helper T Cells

T-cells are essential to both your immune system and your overall health. They play such an important role in protecting you from germs that you couldn’t survive without them. Ask your healthcare provider about how often you should be monitored if your T-cell count is low. Take all medications as directed. In the meantime, take care of yourself by putting healthy habits into place to protect yourself from getting sick.


What are the 3 types of T cells and what do they do? ›

Cytotoxic T cell - Adaptive CD8+ immune cell that kill infected cells when activated. Dendritic cell - A type of antigen presenting cell that processes pathogens and foreign proteins. Presents peptides to T cells. Helper T cell - Adaptive CD4+ immune cell that produces cytokines when activated.

What are these T cells and what are their functions? ›

T cells express a receptor with the potential to recognize diverse antigens from pathogens, tumors, and the environment, and also maintain immunological memory and self-tolerance. T cells are also implicated as major drivers of many inflammatory and autoimmune diseases.

What are the 4 types of T cells quizlet? ›

  • Cytotoxic T Cells( CD8 cells) Destroys host cells that harbour anything foreign. ...
  • Helper T Cells(CD4 cells) Modulate activities of OTHER immune cells.
  • Supressor T Cells. Turn off an immune response.
  • Memory T Cells. ...
  • B lymphocytes. ...
  • T lymphocytes.

What is the main function of T cells quizlet? ›

T cells are important for cell-mediated immunity (resistance to disease organisms resulting from the actions of T cells). Cytotoxic T cells kill infected cells and tumor cells directly. Helper T cells release different substances that attract macrophages into the area around the enemy cells.

What are the major types of T cells? ›

T-cell function is dependent on the type of T cell. The major T cells are CD8+ T cells, CD4+ T cells, and T regulatory cells (i.e., suppressor T cells).

What are the different types of T cells and describe the role each one of them play in cellular immunity? ›

There are two main types of T-cells: Helper T-cells stimulate B-cells to make antibodies and help killer cells develop. Killer T-cells directly kill cells that have already been infected by a foreign invader.

What are the two main functions of T cells? ›

As part of the adaptive immune response, they may recognise foreign antigens and can kill infected cells. They may also act as 'helper' cells by interacting with B cells, maturing them to become producers of antibodies.

What is a functional T cell? ›

Functional T cells are critical to host defense against infection. It has been reported that functional T cells as determined by their cytokine production represent antigen-specific T cells in infectious disease models.

What are the 4 types of helper T cells? ›

CD4 T cells, as a key component of the immune system, are central in orchestrating adaptive immune responses. After decades of investigation, five major CD4 T helper cell (Th) subsets have been identified: Th1, Th2, Th17, Treg (T regulatory), and Tfh (follicular T helper) cells.

What are the 3 main functions of helper T cells? ›

Helper T cells are arguably the most important cells in adaptive immunity, as they are required for almost all adaptive immune responses. They not only help activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells.

What role do T 4 cells play in the immune system? ›

CD4 T lymphocytes (CD4 cells) help coordinate the immune response by stimulating other immune cells, such as macrophages, B lymphocytes (B cells), and CD8 T lymphocytes (CD8 cells), to fight infection.

What is positive vs negative selection T cells? ›

In positive selection, T cells in the thymus that bind moderately to MHC complexes receive survival signals (middle). However, T cells whose TCRs bind too strongly to MHC complexes, and will likely be self-reactive, are killed in the process of negative selection (bottom).

What are the roles of Th1 Th2 and Treg lymphocytes? ›

T cells differentiate into Th1 or Th2 cells upon maturation to influence different patterns of the immune response. Th1 and Th2 cells regulate each other and their responses are inhibited by Treg cells. With noisy external stimulation, Th1/Th2 cell differentiation can be dynamically balanced.

What is CD4 and CD8 T cells? ›

CD4 and CD8 are two types of white blood cells in your blood. CD4 cells are also called T-helper cells, T-suppressor cells, and cytotoxic T-cells. They help the body fight infections. CD8 cells are also called cytotoxic T-lymphocytes.

What are the function of the T? ›

What is the T Function? The T Function[1] is categorized under Excel Text functions. It will test if the value provided is text or not. If it is text, then the function will return the text.

What is one of the main functions of T cells? ›

T cells (also called T lymphocytes) are major components of the adaptive immune system. Their roles include directly killing infected host cells, activating other immune cells, producing cytokines and regulating the immune response.

How many T cells are in the human body? ›

There are 25 million to a billion different T-cells in your body. Each cell has a unique T-cell receptor that can fit with only one kind of antigen, like a lock that can fit with only one shape of key. Antigens and receptors work a lot like a lock and key.

What are the 2 main types of T cells and how do they fight pathogens? ›

They help your immune system fight germs and protect you from disease. There are two main types. Cytotoxic T-cells destroy infected cells. Helper T-cells send signals that direct other immune cells to fight infection.

How many types of T cell receptors does Each T cell have? ›

There are two types of T cell receptor (TCR); alpha beta and gamma delta, both of which are composed of a heterodimer and associated with invariant CD3 complexes on the cell surface.

What are the three signals for T cell activation what are their roles? ›

Primary T cell activation involves the integration of three distinct signals delivered in sequence: (1) anti- gen recognition, (2) costimulation, and (3) cytokine- mediated differentiation and expansion.

What are the main two types of T cells that you need to remember choose two? ›

There are many different kinds of T cells, but the two most important are CD8+ T cells, also called cytotoxic T cells, and CD4+ T cells, or helper T cells. CD8+ T cells recognize and kill pathogens, and CD4+ T cells tell other parts of the immune system to come help fight infections.

Which is the most common type of T cell? ›

There are several types of T cells; the most common and well-known are the CD4+ T cells (helper T cells) and CD8+ T Cells (cytotoxic T cells, or killer T cells).

What do type 2 helper T cells do? ›

Th2 cells mediate the activation and maintenance of the humoral, or antibody-mediated, immune response against extracellular parasites, bacteria, allergens, and toxins. Th2 cells mediate these functions by producing various cytokines such as IL-4, IL-5, IL-6, IL-9, IL-13, and IL-17E (IL-25).

What is the function of cytotoxic T cells? ›

A type of immune cell that can kill certain cells, including foreign cells, cancer cells, and cells infected with a virus. Cytotoxic T cells can be separated from other blood cells, grown in the laboratory, and then given to a patient to kill cancer cells.

Which T cell is important in preventing autoimmune? ›

In conclusion, helper T cells play a very important role in the pathogenesis of autoimmune diseases. They not only participate in B cell-mediated autoimmune diseases but also promote B cells to differentiate into plasma cells and produce autoantibodies.

Which type of T cell is most effective against viruses? ›

Cytotoxic T lymphocytes, natural killer (NK) cells and antiviral macrophages can recognize and kill virus-infected cells. Helper T cells can recognize virus-infected cells and produce a number of important cytokines.

What are the 4 types of T helper cells? ›

CD4 T cells, as a key component of the immune system, are central in orchestrating adaptive immune responses. After decades of investigation, five major CD4 T helper cell (Th) subsets have been identified: Th1, Th2, Th17, Treg (T regulatory), and Tfh (follicular T helper) cells.

What is the function of t4 or helper T cells? ›

Helper T-cells are a type of immune cell. When they sense an infection, they activate other immune cells to fight it. They may activate cytotoxic T-cells or they may activate B-cells, which produce antibodies. Your helper T-cells are one the most important types of cells involved in your adaptive immune response.

What are the two types of T cells quizlet? ›

Terms in this set (5)
  • T Cells. Activate or suppress immune response. ...
  • 3 Types of T Cells. Helper T cells: ...
  • Helper T Cells. -interact with antigen presented on surface of B cell (MHC II) to determine if self or nonself. ...
  • Cytotoxic T Cells. -recognize antigen presented on MHC I molecules. ...
  • Regulatory T Cells.

What is the function of CD4 and CD8 T cells? ›

CD4+T cells along with CD8+T cells make up the majority of T-lymphocytes. CD4+T cells after being activated and differentiated into distinct effector subtypes play a major role in mediating immune response through the secretion of specific cytokines.

What are the main functions of CD4 and CD8 T cells? ›

Main Function of Both CD4 and CD8 Is to Enhance Lck Recruitment, Not Stabilize TCR–pMHC Interactions. Although CD4 does not stabilize TCR–pMHC interactions (9, 13, 14), like CD8, it does enhance T-cell responses (1, 9).

What is the main function of suppressor T cells? ›

A type of immune cell that blocks the actions of some other types of lymphocytes, to keep the immune system from becoming over-active.

What do regulatory T cells do? ›

Regulatory T cells (Tregs) are a specialized subpopulation of T cells that act to suppress immune response, thereby maintaining homeostasis and self-tolerance. It has been shown that Tregs are able to inhibit T cell proliferation and cytokine production and play a critical role in preventing autoimmunity.

What is the function of T3 and T4 cells? ›

The thyroid gland releases triiodothyronine (T3) and thyroxine (T4). These hormones play an important role in regulation of your weight, energy levels, internal temperature, skin, hair, nail growth, metabolism and is an important part of the endocrine system.

What is the difference between Th1 and Th2 T cells? ›

Th1 cells mainly develop following infections by intracellular bacteria and some viruses, whereas Th2 cells predominate in response to infestations by gastrointestinal nematodes.

What is the functional difference between Th1 Th2 and Th17 cells? ›

In broad terms, Th1 cells mediate a cellular immune response and Th2 cells potentiate a humoral response. Th1, Th2 and Th17 populations, and the cytokines they release, are antagonistic to each other and one or the other subtype is dominant in response to a particular pathogen at any one time.

What is the difference between CD4 Th1 and Th2? ›

The Th1 subset of CD4+ T cells secretes cytokines usually associated with inflammation, such as IFN-gamma and TNF and induces cell-mediated immune responses. The Th2 subset produces cytokines such as IL-4 and IL-5 that help B cells to proliferate and differentiate and is associated with humoral-type immune responses.


1. B Cells vs T Cells | B Lymphocytes vs T Lymphocytes - Adaptive Immunity - Mechanism
2. T Cell Development and Maturation - T Cells are COOL!
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3. Immune System
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4. Helper T cells | Immune system physiology | NCLEX-RN | Khan Academy
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5. Immune Response Explained: T-Cell Activation
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6. Types of T lymphocytes - chapter 35 (part 8) Guyton and Hall text book of physiology.
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