What are T cells? How are they important to our body's immune system?

Have you ever thought that inside our bodies, like little soldiers, there are a group of invisible guards who are constantly fighting off disease-causing germs and saving us? T cells are a very important, heroic group of cells in our bodies. So today we are going to talk about these amazing T cells. To be precise, what are they, what are their benefits to our bodies, and what happens if they decrease or increase?

What are T cells? Let's understand it simply!

Okay, so T cells are a type of white blood cell in our body. Scientifically speaking, they are called lymphocytes . You may have heard that our body has an immune system . Lymphocytes are the main soldiers in that system. This immune system is what fights pathogens that enter our body, that is, germs like viruses, bacteria, and fungi. Not only that, this system also helps to destroy cells that are harmful to our body, like cancer cells.

Among these lymphocytes in our body, there are also another type called B cells, as well as T cells . Together, these two protect our body. What B cells do is make a type of protein called antibodies . These antibodies are what fight germs. But T cells are a little different. They go straight to destroy those harmful germs, and they also signal other cells in the immune system, saying, "There's a problem here, come quickly!" and they also join the fight. It's like a commander in a war.

What are the main types of T cells?

There are two main types of T cells. Let's see what they are:

• Cytotoxic T cells: These are also called CD8+ cells because they have a receptor called `CD8` on their membrane. "Cyto" means cell, and "toxic" means poisonous. So, as the name suggests, these cells seek out and destroy things like our own cells infected with viruses, bacteria, and cancer cells. To be precise, they are like the "killer cells" in our body.

• Helper T cells: These are called CD4+ cells because they have a receptor called ``CD4`` on them. Unlike cytotoxic T cells, these helper T cells don't go out and attack anyone directly. Instead, they send signals to other immune cells (that is, cytotoxic T cells, B cells, and another type of white blood cell called macrophages) . It is these helper T cells that give instructions, like, "This is how you should fight, this is how you should attack."

In addition to these two main types, there is a special group called regulatory T cells . Sometimes these are also called suppressor cells . Their job is to reduce the activity of other T cells when necessary. Imagine, sometimes our T cells can become too active and start attacking our own healthy cells. At such times, these regulatory T cells intervene and control that unnecessary attack by saying, "Okay, okay, stop now."

What kind of service do T cells provide to our bodies?

T cells are the main fighters in our adaptive immune system . Think of the adaptive immune system as a very intelligent, specialized defense system. It is constantly on the lookout for anything foreign or harmful that might be entering our bodies. Once it detects something, it mounts a specialized defense to fight it off.

The amazing thing is, each T cell is designed to fight only one specific invader. That is, a single T cell can only attack one type of virus. It cannot attack any other virus. So, when our immune system recognizes an invader, it finds the right T cell and recruits it to fight it. Then that T cell copies itself and makes many more T cells to defeat that invader. The T cells that join this fight are called effector cells . If our immune system is working properly, these effector T cells destroy the threat and protect us from disease.

Not only that, but T cells protect us even after the invader is gone. Some T cells, instead of being effector cells, become memory cells . These memory cells don't fight, but they remember the invader well from the previous encounter. So if the invader comes back, our immune system can quickly recognize it and use the old memory to mount a rapid counterattack.

How do T cells work?

T cells start working after they are activated. Several steps must occur before a T cell can become activated:

1. First, a special cell called an Antigen-Presenting Cell (APC) finds a part of the invader (e.g., a virus) and attaches it to a structure called the Major Histocompatibility Complex (MHC) . This step is very important, because a T cell can only recognize an invader if it has attached itself to that MHC.

2. Next, the T cell comes and binds to that MHC. There are two types of MHC, one for each type of T cell. The `CD8` receptor on a cytotoxic T cell can only bind to `MHC-I`. The `CD4` receptor on a helper T cell can only bind to `MHC-II`.

3. When the T cell is properly attached to all of the matching parts, it becomes activated. This attachment is very important, because it ensures that this is the exact T cell that should attack that invader.

An activated cytotoxic T cell goes straight to kill infected cells or cancer cells. An activated helper T cell sends signals to other immune cells, telling them to "do these things."

Where are T cells located in our body?

The location of T cells varies depending on the stage of the cell's life cycle.

• Bone marrow: T cells first develop in the bone marrow, a soft tissue inside our bones. Like all other blood cells, they start out as hematopoietic stem cells . These stem cells can develop into any type of blood cell.
• Thymus: These T cells then travel to the thymus gland , an organ in the upper middle of our chest, to mature. At this point, these immature T cells are called thymocytes . The thymus is like a "boot camp" for T cells. Once inside, the T cells have to undergo various tests. For example, they are tested to see if they can properly bind to MHC and if they will attack healthy cells in our body. They also find the right receptor for them, namely `CD4` (for helper T cells) or `CD8` (for cytotoxic T cells). Only the T cells that pass all these tests are released to move around in our body.
• Lymphatic tissue and circulatory system: Fully mature T cells then travel to the tissues and organs of our lymphatic system (e.g., spleen, tonsils, lymph nodes). Some also circulate in our blood. These T cells remain in our bodies, ready to serve until their services are needed.

You know, when we're young, our thymus is very large, but as we age, it gradually shrinks. Relatedly, around the age of 20, the release of new T cells from the thymus decreases significantly. After that, the supply of different T cells in our body depends on the ability of our body to replicate the T cells we already have.

What are the common diseases that affect T cells?

There are several types of autoimmune diseases and immunodeficiency disorders that can affect T cells. In autoimmune diseases, our immune system mistakenly attacks our own healthy cells. Immunodeficiency diseases are conditions that are either congenital or acquired, and weaken the immune system.

Some of the conditions that can affect T cells include:

• Acute Lymphocytic Leukemia (ALL): This is a type of cancer that begins in the blood and bone marrow.
• Adult Hodgkin Lymphoma: A type of blood cancer that begins in the lymphatic system.
• T-cell Lymphomas: A group of blood cancers that begin in T cells. They can affect a variety of tissues, most commonly the skin, but can also affect lymph nodes and subcutaneous tissue.
• Chronic T-cell Leukemia (Chronic T-cell Leukemia / T-cell Prolymphocytic Leukemia): A blood cancer that begins in T cells. It can affect the bone marrow, blood, and lymph nodes.
• DiGeorge Syndrome: This is a genetic disorder that can prevent the body from making enough healthy T cells.
• HIV (Human Immunodeficiency Virus): This virus attacks our white blood cells (especially `CD4+` T cells), which can lead to a condition called `AIDS`.
• Job Syndrome: This is a rare immune system disorder that causes frequent infections.
• Severe Combined Immunodeficiency (SCID): This is a rare genetic disorder that weakens the immune system due to problems with T cells and other lymphocytes.
• Thymic Aplasia: This is when the thymus does not develop properly at birth.
• Wiskott-Aldrich Syndrome: This is a rare genetic condition that causes immune system problems (including abnormal white blood cells).

What is the normal size of T cells?

The normal range for T cells can vary depending on the lab that does your T cell count. In general, for a healthy adult, a CD4 count, or helper T cell count, is between 500 and 1,200 cells per cubic millimeter. A CD8 count, or cytotoxic T cell count, is between 150 and 1,000 cells per cubic millimeter.

Your doctor can explain to you what a normal result looks like for you, depending on your condition and general health.

What does it mean if you have low T cells?

Low T cells can mean that there are various problems that affect your immune system. It could be a condition that you are born with, where your body cannot make enough T cells. Or, it could be a condition that you develop later, such as HIV, that causes your body to produce fewer T cells. T cells can also be low as a side effect of some treatments or medications.

Whatever the cause, if you lose enough T cells, your body has a harder time defending itself against invaders. A severe decrease in T cells can even be life-threatening.

What happens if T cells increase?

An excess of T cells is not usually seen. An excess of T cells may mean that your body is producing more T cells to fight an infection. Or, an excess of T cells can be a symptom of some types of cancer.

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

If your doctor suspects there is a problem with your immune system, he or she may order a T cell count (also called a CD4 count) . Or, they may order another test called a CD4 to CD8 ratio T-cell test . This measures how many cytotoxic T cells you have in your body compared to the number of helper T cells.

T-cell counts are especially useful if you are HIV-infected. They allow your doctor to monitor the health of your immune system and assess how well your treatment is working.

How do I increase my T cells?

Ask your doctor about medications and treatments that can boost your T cells. In the meantime, you can do things that will help your immune system. Sometimes, the best way to protect your T cells is to avoid relying on them too much. That means staying away from germs and taking good care of your body.

You can do these things:

• Eat a good, balanced diet.
• Get all your vaccinations on time.
• Avoid alcohol, or use it very sparingly.
• If you smoke or vape, stop.
• Get at least seven to eight hours of sleep every night.
• Engage in at least 150 minutes of moderate exercise per week.
• Wear a face mask indoors, especially in poorly ventilated areas.
• Wash your hands often with soap or use hand sanitizer.

What is the difference between T cells and antibodies?

Both T cells and antibodies protect us from pathogens, but they perform different functions in our immune system. You may remember what we said about B cells. It's the B cells (not the T cells) that make antibodies. Antibodies are special proteins that kill those harmful invaders. While B cells send antibodies to kill harmful cells, cytotoxic T cells go straight to kill those harmful cells.

Finally, things to remember

T cells are essential to your immune system and your overall health. They play such an important role in protecting you from germs that we couldn't live without them. If your T cell count is low, ask your doctor how often you should have it checked. Take all your prescribed medications exactly as prescribed. In the meantime, take care of yourself by following good health habits to protect yourself from illness. After all, a healthy life is the greatest asset!

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