Psoriasis occurs when something goes wrong with your immune system. Your immune cells become overactive and attack your skin and joints. T cells, a type of immune cell, play an important role in causing psoriasis.

The Immune System and Psoriasis

The immune system helps fight germs, including bacteria, viruses, and fungi, keeping you safe from infections. It also protects against other foreign substances, such as toxins and harmful chemicals. Many different types of cells, tissues, and organs make up the immune system.

Without a healthy immune system, you may get sick more often. You may have more frequent and more severe infections that are harder to treat.

On the other hand, your immune system can also work too well. People with autoimmune disorders — including psoriasis and psoriatic arthritis (PsA) — have an immune system that is strong but misguided. It starts attacking healthy tissues.

What Are T Cells?

T cells, also called T lymphocytes, are white blood cells that play an important role in your immune system. These cells help recognize the immune response and clear out infections.

There are three main types of T cells:

• Helper T cells recognize signs of an infection. They activate and send out instructions to other cells of the immune system, including killer T cells, to coordinate an immune response.
• Killer T cells find cells in your body that have become infected by viruses, produce cytotoxins (chemicals that destroy the infected cells), and make more copies of themselves so that your body is better protected.
• Regulatory T cells, or Tregs, help shut off immune responses once a threat is neutralized and prevent the immune system from attacking the body.

Normally, your immune system has ways of telling infected cells and healthy cells apart. Germs and other foreign substances display antigens — molecules that your immune system can recognize and respond to. When your T cells encounter antigens that are part of a toxin or foreign substance, they begin an attack.

On the other hand, your body’s cells contain self-antigens. These molecules act as a marker or tag that tells your T cells that the cell is safe. Healthy T cells ignore cells with self-antigens.

T Cells and Psoriasis

In psoriasis, there are two main problems when it comes to T cells. First, there are too many T cells and other types of immune cells. People with psoriasis have more T cells in the skin than usual. Additionally, people with PsA have high numbers of T cells in the joints.

The other problem in psoriasis is that your T cells are activated when they shouldn’t be. They mistakenly view your healthy cells as an outside threat and begin attacking them, despite the self-antigen tags. The T cells can also produce cytokines — chemicals that signal to other immune cells, turn on other parts of the immune system, and create inflammation.

Once your T cells start activating the immune system, the excess inflammation can damage the skin and joint tissues. Certain factors, such as weather, stress, or illness, can trigger an immune response, leading to flare-ups. Symptoms such as discolored or scaly skin lesions, pitted or discolored nails, or joint pain and swelling can ramp up during flares.

Why Do T Cells Become Abnormal in Psoriasis?

Health experts don’t yet fully understand why T cells behave unusually in people with psoriasis. Researchers are continuing to study this question. As they learn more, they may come up with treatments that work more effectively to control the immune system and prevent psoriasis symptoms.

One possible cause of abnormal T cells in psoriasis is that the cells may mistake healthy tissue for germs. For example, T cells may be activated in order to fight off Streptococci — bacteria that cause many different infections, including strep throat. Some molecules naturally found in the skin are similar to molecules found in this bacteria. T cells that have experience fighting Streptococci may travel to the skin, misread skin molecules as bacteria molecules, and begin attacking again.

Another potential problem is that psoriasis leads to problems with the immune system’s “off” switches. Normally, the immune system operates within a tightly controlled balance — some immune cells and molecules ramp up the immune system, while others dampen it down.

In people with psoriasis, Tregs and other cells that are supposed to turn off the immune system don’t work as well as they should. As a result, the balance shifts toward ramping up, and the immune system is activated more strongly than it should be.

Medications That Target T Cells

Immunosuppressive drugs are often used for the treatment of psoriasis. These medications help calm the immune system, prevent killer T cells from becoming overactive, or neutralize the inflammation-causing molecules that T cells produce.

Biologics

Biologics are medications that block specific cells or molecules within the immune system. Many of these drugs block T cells.

Abatacept (Orencia) is a medication that specifically acts on T cells. Before T cells can do their job, they are activated by other immune cells. Abatacept prevents other cells from interacting with and turning on the T cells.

Some biologics also block cytokines that help activate T cells, increase T cell numbers, or support the immune responses created by T cells. These biologics include:

• IL-17 inhibitors — Secukinumab (Cosentyx), brodalumab (Siliq), and ixekizumab (Taltz)
• IL-23 inhibitors — Tildrakizumab-asmn (Ilumya), guselkumab (Tremfya), and risankizumab-rzaa (Skyrizi)
• IL-12 and IL-23 inhibitors — Ustekinumab (Stelara)

Medications like etanercept (Enbrel), infliximab (Remicade), adalimumab (Humira), and golimumab (Simponi) block an immune protein called tumor necrosis (TNF)-alpha. This protein causes inflammation, so TNF-alpha inhibitor drugs block it to reduce symptoms of psoriasis and PsA.

TNF-alpha inhibitors affect T cells in a few different ways. They can prevent helper T cells from becoming activated and encourage immune cells to make anti-inflammatory chemicals. These drugs may also boost the numbers of Tregs, the cells that help calm the immune system.

Nonbiologic Medications

Some nonbiologic psoriasis treatment options also target T cells. Cyclosporine (Neoral) is a drug prescribed for severe psoriasis. This medication prevents T cells from making extra copies of themselves. It also blocks the T cells’ production of cytokines.

Methotrexate, sold under the brand name Otrexup, is another medication used to treat severe psoriasis as well as PsA. This drug can slow down new skin cells from being formed and combat inflammation. Taking methotrexate can lead to fewer helper T cells that activate the immune system, as well as higher levels of Tregs.

Light Therapy

Light therapy involving natural sunlight or artificial lights in a doctor’s office can help ease psoriasis symptoms. These treatments, also called phototherapy, may also involve taking a drug that sensitizes cells to light.

Research has found that light treatments may affect T cells. They may decrease the levels of T cells that cause inflammation. Light therapy may also lead to greater numbers of Tregs and help these cells work better.

Talk With Others Who Understand

On MyPsoriasisTeam, the social network for people with psoriasis and their loved ones, more than 107,000 members come together to ask questions, give advice, and share their stories with others who understand life with psoriasis.

Do you still have questions about T cells and psoriasis? Share your thoughts in the comments below, or start a conversation by posting on MyPsoriasisTeam.