Role of T cells in immune System

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

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 tumour

              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 cells 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 defence to fight it.

              Each T cell is unique in that it’s designed to fight only one type of intruder. Once our 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 our immune system is working properly, these effector T cells destroy the threat, to get rid of infection and disease.

              Our T cells continue to protect you even after the intruder’s gone. Some of our 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, our immune system recognizes it and quickly mounts an attack to destroy.

How do T cells work in the immune system?

T cells work once they’re activated. Several steps are taken 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.

              As already stated in earlier blog (“The thymus gland, training centre of human body soldiers”) our thymus is largest in childhood and shrinks with age. Around age 20, it also starts producing fewer new T cells. From that point on, our immune system relies more on making copies of existing T cells to maintain its defences.

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 leukaemia: 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 leukaemia (T-cell prolymphocytic leukaemia): 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 millimetre 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.

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.

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.

Quote: “Your immune system is your body’s silent guardian—nourish it with good food, movement, rest, and a calm mind, and it will protect you for a lifetime.”