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Antigen-presenting cells display three types of protein molecules on their surface that have a role in activating a T cell to become an effector cell: (1) MHC proteins, which present foreign antigen to the T cell receptor, (2) costimulatory proteins, which bind to complementary receptors on the T cell surface, and (3) cell-cell adhesion molecules, which enable a T cell to bind to the antigen ...
- Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter
- 2002
- 2002
Aug 31, 2023 · Figure 12.3A. 1 12.3 A. 1: Epitope-Specific Receptors on the Surface of B- and T-Lymphocytes. B-lymphocytes have B-cell receptors that recognize epitopes directly on antigens. T-lymphocytes have TCR molecules that recognize epitopes only after they have been placed on cells of the body by way of MHC molecules.
- Overview
- Function
- Anatomy
- Conditions and Disorders
- Care
- Additional Common Questions
T-cells are a type of white blood cell called lymphocytes. 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.
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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.
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. Advertisement
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 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.
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.
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. Medically Reviewed Last reviewed by a Cleveland Clinic medical professional on 01/17/2023. Learn more about our editorial process.
The T cell receptor (TCR) on both CD4 + helper T cells and CD8 + cytotoxic T cells binds to the antigen as it is held in a structure called the MHC complex, on the surface of the APC. This triggers initial activation of the T cells. The CD4 and CD8 molecules then bind to the MHC molecule too, stabilising the whole structure.
A T-cell receptor recognizes antigen in the form of a complex of a foreign peptide bound to an MHC molecule. Antigen recognition by T-cell receptors clearly differs from recognition by B-cell receptors and antibodies. Antigen recognition by B cells involves direct binding of immunoglobulin to the intact antigen and, as discussed in Section 3-8 ...
- Charles A Janeway, Paul Travers, Mark Walport, Mark J Shlomchik
- 2001
- 2001
T cell. T cells are one of the important types of white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their cell surface. T cells are born from hematopoietic stem cells, [1] found in the bone marrow.
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Jan 1, 2020 · Like mechanosensing, TCR allostery could explain the exceptional ability of a single pMHC molecule binding to an exclusively monomeric TCR to initiate T-cell signaling without any requirement for ligand-induced receptor oligomerization and before formation of the immunological synapse . However, the enormous sequence diversity of TCRs presents a major challenge for allosteric models of early T ...
