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.
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.
There are two main types of T-cells:
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.
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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.
T-cells work once they’re activated. Several steps have to happen before a T-cell activation:
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.
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.
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:
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.
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.
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.
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.
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.
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.
Last reviewed by a Cleveland Clinic medical professional on 01/17/2023.
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