Overview
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.
Function
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:
- 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.
- 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.
- 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.
Anatomy
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.
- 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.
- 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.
- 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.
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.
Care
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
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.
FAQs
T Cells: Types and Function? ›
There are two major types of T cells: the helper T cell and the cytotoxic T cell. As the names suggest helper T cells 'help' other cells of the immune system, whilst cytotoxic T cells kill virally infected cells and tumours.
What are the 3 main types of T cells? ›The major T cells are CD8+ T cells, CD4+ T cells, and T regulatory cells (i.e., suppressor T cells).
What are three types of T cells and indicate what they do? ›Types of T cells: Helper T cells (CD4 cells): release T cell cytokines and help the activity of other immune cells. Cytotoxic T cells: kills target cells by inducing apoptosis. Regulatory T cells: suppress other T cell immune responses.
What do CD4 and CD8 T cells do? ›CD4 T cells play critical roles in controlling viral infections by promoting CD8 T cell responses as well as humoral immunity. While primary antiviral CD8 T cell immunity is elicited prior to production of neutralizing antibodies (Ab), humoral responses provide a first line of defense against secondary infection.
What are the main functions of T cells? ›T cells are part of the immune system and develop from stem cells in the bone marrow. They help protect the body from infection and may help fight cancer. Also called T lymphocyte and thymocyte. Blood cell development.
What is meant by CD3 CD4 and CD8? ›CD3 is a common T-lymphocyte antigen, present on the surface of all T-lymphocytes. CD4 is an antigen present on the surface of T-helper-lymphocytes (T-helper cells), monocytes, and some white blood cells. activated granules. CD8 is an antigen present on the surface of cytotoxic and inhibitory T cells.
What are killer T cells? ›(KIH-ler ... sel) A type of immune cell that can kill certain cells, including foreign cells, cancer cells, and cells infected with a virus. Killer T cells can be separated from other blood cells, grown in the laboratory, and then given to a patient to kill cancer cells.
What is the difference between T cells and T lymphocytes? ›T cell, also called T lymphocyte, type of leukocyte (white blood cell) that is an essential part of the immune system. T cells are one of two primary types of lymphocytes—B cells being the second type—that determine the specificity of immune response to antigens (foreign substances) in the body.
Which of the four types of T cells only the T cells destroy infected body cells? ›There are two types of T-cells in your body: Helper T-cells and Killer T-cells. Killer T-cells do the work of destroying the infected cells. The Helper T-cells coordinate the attack.
What are T cells Type 2? ›Th2 cells stimulate and recruit specialized subsets of immune cells, such as eosinophils and basophils, to the site of infection or in response to allergens or toxins leading to tissue eosinophilia and mast cell hyperplasia. They induce mucus production, goblet cell metaplasia, and airway hyper-responsiveness.
What do CD8 T cells do? ›
Independent of T cell receptor ligation, CD8 T cells can mount a response against pathogens by secreting cytokines and can defend against tumors by directly killing transformed cells. This innate response has been shown to be beneficial in controlling several types of bacterial infections.
What cell is positive for CD4 and CD8? ›A normal CD4/CD8 ratio is greater than 1.0, with CD4 lymphocytes ranging from 500 to 1200/mm 3 and CD8 lymphocytes ranging from 150 to 1000/mm 3. If your ratio is higher than 1, it means your immune system is strong and you may not have HIV. If your ratio is less than 1, you may have: HIV.
What is the difference between Th1 and Th2 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 three cells are needed to destroy an infected cell? ›Cytotoxic effector cells that can destroy virus-infected cells include cytotoxic T cells, natural killer cells, and activated macrophages.
What increases T cells? ›Vitamin D triggers the body's immune response by preparing the t-cells for action, setting them up to help antibodies attack infections. We get vitamin D from a variety of sources, including certain foods that make up our modern diets, but a neat way to get the vitamin is by heading out and catching some sun.
What is the role of T cell in COVID? ›(2021) studied the T memory response in symptomatic patients further. They showed that both central memory ( T CM ) and effector memory ( T EM ) cells had increased proliferation capacity and had a functional response in the majority of the symptomatic COVID-19 patients.
What are CD3 and CD19 cells? ›Human leukocyte antigen (HLA)-haploidentical donor-derived natural killer (NK) cells that are activated with the cytokine interleukin-15 (IL-15), with immunomodulating and antineoplastic activities.
What does CD3 positive T cells mean? ›A cluster with >20 CD3-positive cells is a candidate indicator for BM involvement in PTCL. Keywords: Peripheral T-cell lymphoma, Bone marrow involvement, CD3 positivity. Peripheral T-cell lymphomas, not otherwise specified (PTCLs) represent approximately 10% of all non-Hodgkin lymphomas [1].
Why is my CD8 so high? ›Elevation and expansion of CD8 T-cells occurs from the very early days of HIV infection, as observed in other acute viral infections. During this phase, the rapid and robust expansion of CD8 T-cells particularly in the viral-specific subsets contributes to a partial control of viraemia [15,16].
What are the 4 types of T cells? ›- Effector Cells. Depending on the APC a naïve cell comes across it can become an effector T cell. ...
- Cytotoxic T Cells. Cytotoxic T Cells, also known as CD8+ cells, have the primary job to kill toxic/target cells. ...
- Helper T Cells. ...
- Regulatory T Cells. ...
- Memory T Cells. ...
- Applications.
How do T cells become activated? ›
They are activated on the surface of antigen-presenting cells, which mature during the innate immune responses triggered by an infection. The innate responses also dictate what kind of effector cell a helper T cell will develop into and thereby determine the nature of the adaptive immune response elicited.
What cell slows or stops the immune response? ›Cytotoxic T cells produce toxic agents to kill their targets, while helper T cells stimulate B cells to make antibodies against the targets and stimulate cytotoxic T cells to become active. Regulatory T cells suppress immune responses, keeping the system in check to prevent overactive immune responses.
Are T cells in blood or lymph? ›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.
In which body system would you find helper T cells? ›Where are helper T-cells located? T-cells start in your bone marrow, the spongey substance that fills some of your bones. They move to your thymus while they're developing. Your thymus helps your T-cells mature, and then circulates them throughout your body.
Which cell component is most connected to your immune system? ›White blood cells are the key players in your immune system. They are made in your bone marrow and are part of the lymphatic system. White blood cells move through blood and tissue throughout your body, looking for foreign invaders (microbes) such as bacteria, viruses, parasites and fungi.
Which type of T cell is most directly effective against viruses? ›An effective immune response against viral infections depends on the activation of cytotoxic T cells that can clear infection by killing virus-infected cells.
Which type of T cell kills pathogens? ›Armed effector cytotoxic CD8 T cells are essential in host defense against pathogens that live in the cytosol, the commonest of which are viruses. These cytotoxic T cells can kill any cell harboring such pathogens by recognizing foreign peptides that are transported to the cell surface bound to MHC class I molecules.
What is the infection that causes destruction of T cells in the body? ›Human immunodeficiency virus (HIV) is the most well-known example of a chronic immune system condition caused by an infection. HIV infects T cells, specifically a type of T cell called CD4+ T cells.
Are natural killer cells T cells? ›Natural Killer (NK) Cells are lymphocytes in the same family as T and B cells, coming from a common progenitor. However, as cells of the innate immune system, NK cells are classified as group I Innate Lymphocytes (ILCs) and respond quickly to a wide variety of pathological challenges.
What do double negative T cells do? ›Figure 2 DN T cells participate in both innate and adaptive immunity. Based on Ag-TCR-specific recognition, DN T cells can inhibit or eliminate adaptive immune cells, suppressing diseases caused by immune responses. DN T cells can also secrete various cytokines to mediate innate immune responses.
How many types of T cells are associated with immune system? ›
There are two major types of T cells: the helper T cell and the cytotoxic T cell. As the names suggest helper T cells 'help' other cells of the immune system, whilst cytotoxic T cells kill virally infected cells and tumours.
Are T cells CD4 or CD8? ›CD4 T cells are MHC-II restricted and pre-programmed for helper functions, whereas CD8 T cells are MHC I-restricted and pre-programmed for cytotoxic functions. CD4 and CD8 subsets constitute the bulk of αβ T cells and are the main component of T-mediated immune responses.
What are CD4 T cells also called? ›CD4+ T cells, or helper T cells, are one type of lymphocyte that helps coordinate the immune response against infection and disease.
What is the difference between CD8 and cytotoxic T cells? ›The CD8 receptor interacts with cells called major histocompatibility complex (MHC) Class I molecules to recognize when healthy cells are infected. When the CD8 receptor recognizes an infected cell, it activates the cytotoxic T-cells. The cytotoxic T-cells create molecules designed to destroy the infection.
What causes CD4 to drop? ›If you don't have HIV, a low CD4 count may be caused by an infection. Cancer chemotherapy and medicines that weaken your immune system may also cause low CD4 counts. In certain cases, the cause of a low CD4 count is unknown, but this is uncommon.
What is CD8 a marker for? ›The CD8 molecule is a marker for cytotoxic T cell population. It is expressed in T cell lymphoblastic lymphoma and hypo-pigmented mycosis fungoides.
What does CD8 positive mean? ›CD8-positive T cells are a critical subpopulation of MHC class I-restricted T cell and are mediators of adaptive immunity. They include cytotoxic T cells, which are important for killing cancerous or virally infected cells, and CD8-positive suppressor T cells, which restrain certain types of immune response.
What do Th17 cells do? ›Th17 cells play a role in host defense against extracellular pathogens, particularly at the mucosal and epithelial barriers, but aberrant activation has been linked to the pathogenesis of various autoimmune diseases [5].
Is Th1 an autoimmune disease or Th2? ›Th1 cells promote cellular immunity and are involved in the development of autoimmune diseases; Th2 cells mediate humoral immunity and are involved in allergic immune responses.
Are Th2 cells pro or anti-inflammatory? ›Th2-related cytokinees (IL-4 and IL-10) are associated with humoral immunity and anti-inflammatory properties.
What kills a virus in your body? ›
Medicine that treats viral infections is called an antiviral. These medicines usually stop a virus from making copies of itself. They also may stop a virus from going into or leaving a cell. Many antivirals are made to target the virus and not the host cell.
Which cells will keep you from becoming infected again? ›T cells protect us from infection.
They also direct the immune response by helping B lymphocytes to eliminate invading pathogens.
(NA-chuh-rul KIH-ler sel) A type of immune cell that has granules (small particles) with enzymes that can kill tumor cells or cells infected with a virus. A natural killer cell is a type of white blood cell. Also called NK cell and NK-LGL.
What foods trigger T cells? ›Your immune system needs protein to create t-cells so it's important to eat foods that are rich in protein. Look for 3 to 4 ounce portions of lean meat or protein. You can eat skinless chicken, fish, eggs, lentils, beans, and soy. Avoid eating saturated fats such as red meats, fried meats, or chicken with the skin.
What happens to your T cells after Covid? ›Within 2-3 weeks after symptom onset, all COVID-19 patients developed anti-nucleocapsid IgG and spike-neutralizing IgG as well as SARS-CoV-2-specific T cell responses. In addition, we found alterations in follicular T helper (TFH) cell populations, such as enhanced TFH-TH2 following recovery from COVID-19.
What causes problems with T cells? ›What Abnormal Results Mean. Higher than normal T-cell levels may be due to: Cancer, such as acute lymphocytic leukemia or multiple myeloma. Infections, such as hepatitis or mononucleosis.
What happens to T cells after COVID vaccine? ›Uninfected vaccine recipients experienced a greater than 60-fold rise in their levels of SARS-CoV-2-targeting killer T cells. By six weeks after their first dose, one in every five of their killer T cells was SARS-CoV-2-specific.
What does COVID vaccine do to T cells? ›In the group of participants who did not previously have COVID-19, they found that the first vaccine dose elicited a rapid and strong response from helper T cells called CD4 T cells—some of which help marshal an antibody response, while others stimulate the proliferation of CD8 killer T cells.
Does the COVID vaccine suppress T cells? ›Two doses of the mRNA COVID-19 vaccine were seen to elicit significantly lower T-cell responses compared to healthy individuals and even patients with HIV and primary immunodeficiencies.
What are the 2 main types of T-cells and how do they fight pathogens? ›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 or cytotoxic T-cells directly kill cells that have already been infected by a foreign invader.
What are the 3 types of cells that helper T-cells produce? ›
Cytotoxic T-cells, which fight infections. Regulatory T-cells, which regulate or suppress other immune cells when needed. NKT-cells, which can enhance immunity in general.
What are the 3 types of signals in T cell activation? ›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.
How can I increase my T-cells naturally? ›- Get some sun. The same t-cells that benefit from sleep form part of the body's response to viruses and bacteria, and one of the key ingredients that 'primes' those t-cells for action is vitamin D. ...
- Reach for vitamin C foods. ...
- Incorporate garlic in your diet.
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 type of T cell recognizes infected cells and kills them? ›Killer T cells are called “cytotoxic” or “cytolytic” because they possess special molecular weapons that enable them to directly attack and destroy other cells displaying targets they recognize, for example, a virus-infected cell or even a cancerous cell.
What are the 4 types of CD4 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 is the difference between Th1 and Th2? ›Th1 cells mainly develop following infections by intracellular bacteria and some viruses, whereas Th2 cells predominate in response to infestations by gastrointestinal nematodes.
What do cytotoxic T cells do? ›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 cytokine is most important in T cell activation? ›IL-2 is a potent T cell growth factor which is essential for the long-term proliferation of activated T cells.
What cytokines are needed for T cell activation? ›The activation and proliferation of CAR-T cells release primary cytokines such as IL1, IFN-γ, and TNF, which induce the activation of other immune cells, such as macrophages, DCs, and monocytes (241). These cells then produce excessive amounts of secondary cytokines, such as IL6, IL10, and IL5 (242).
What cells are necessary to activate T cells? ›
Naïve T cells require at least two signals for activation. Both are provided by an antigen-presenting cell, which is usually a dendritic cell: signal 1 is provided by MHC-peptide complexes binding to T cell receptors, while signal 2 is mainly provided by B7 costimulatory proteins binding to CD28 on the T cell surface.
What vitamin increases T cells? ›Higher levels of vitamin D may induce many different anti-inflammatory functions including increasing the number and/or function of T regulatory cells (Tregs).
What vitamin builds T cells? ›Vitamin C Promotes Maturation of T-Cells.