What is the thymus gland?

The thymus plays a vital role in developing disease-fighting T cells and releases hormones that help regulate processes in your body.

This article explores thymus function and hormones, and how health conditions that affect the thymus can impact immunity and autoimmunity.

We cover:

• What is the thymus?
• What is the function of the thymus?
• What hormones does the thymus produce?
• When does the thymus disappear?
• What can go wrong with the thymus?

What is the thymus?
 

The thymus gland plays an important role in your immune system. It also has a messaging role in the endocrine system, which makes and releases hormones that control most of your body’s functions and processes.

The thymus sits in your upper chest, behind your breastbone (sternum). And its name comes from its resemblance to the bud of a thyme plant (thymus in Latin).

What is the function of the thymus?
 

The primary function of the thymus is producing and training T cells, specialised white blood cells (lymphocytes) that help fight infection and disease.

The thymus is part of the adaptive immune system, which kicks in when your body’s first line of defence—the innate immune system—fails to destroy germs that enter your body.

While innate immunity only offers a general response to broad categories of germs, the adaptive immune system can recognise specific ones and sends out specialised cells and antibodies to attack them.

The thymus makes many types of specialist cells, each with a different function. For instance, some make antibodies that attack viruses and bacteria, while others can detect and attack cancer cells and help prevent autoimmune diseases [1].

What hormones does the thymus produce?
 

The thymus produces several hormones that help produce mature T cells and support immune function.

Hormones made by the thymus include:

• Thymopoietin, which fuels T-cell production and signals the pituitary gland to release hormones.
• Thymosin and thymulin, which help make specialised types of T cells.
• Thymic humoral factor, a hormone that helps keep the immune system working properly.

The thymus also makes small quantities of hormones produced in other parts of the body. These include melatonin, which helps you sleep, and insulin, which helps control your blood sugar level.

When does the thymus disappear?
 

The thymus may not fully disappear, but it begins to shrink when you reach puberty. As it shrinks, the glandular tissue of the thymus is replaced by fat.

This genetically programmed process is called thymic involution, and it means that our ability to mature new T cells declines significantly with age.

Although this process is irreversible, the thymus matures all the T cells you need before you hit puberty (many of them are made before you’re born).

What can go wrong with the thymus?
 

Certain conditions, as well as advancing age, can lead to health issues with your thymus gland [2]. These conditions range from genetic disorders present at birth to diseases most commonly seen in older adults.

Conditions that affect the thymus gland include:

• DiGeorge syndrome: a condition where the thymus is absent or underdeveloped at birth. This causes a T-cell deficiency that increases the risk of infection and immune system problems.
• Thymic hyperplasia: this condition causes the thymus to become swollen and inflamed. It can occur with autoimmune conditions such as myasthenia gravis and rheumatoid arthritis.
• Thymus cancer: a rare condition, more common in people over 50 [3]. The two main type of thymus cancer are:

1. Thymomas—tumours that grow slowly and rarely spread beyond the thymus.
2. Thymic carcinomas—a rarer form of thymus cancer than a thymoma. Thymic carcinomas also grow faster and are more likely to spread to other parts of the body, which makes them more difficult to treat.

Symptoms of thymus cancer include [3]:

• Chest pain
• Hoarse voice
• Persistent cough
• Shortness of breath

If you’re experiencing any of these symptoms, we recommend you see your doctor. Thymus cancer is unlikely to be the cause of your symptoms, but a medical evaluation can help you pinpoint any issues and take steps to improve your health.

Sometimes, people with thymomas can develop other immune conditions, such as:

• Hypogammaglobulinemia—an immune system disorder where levels of immunoglobulins, or antibodies, are too low.
• Lupus, or systemic lupus erythematosus (SLE)—an autoimmune condition where the body attacks its own tissues, which can cause joint pain, skin rashes, and fatigue.
• Myasthenia gravis (MG)—about 75% of people diagnosed with MG have a problem with thymus function [4]. In MG, the immune system attacks the connections between nerves and muscles, causing weakness and a loss of control.
• Pernicious anaemia—a rare autoimmune condition that prevents the body from absorbing vitamin B12, causing a decrease in red blood cell production.
• Pure red cell aplasia—T cells attack young red blood cells, causing severe anaemia, a lack of oxygen-carrying red blood cells.
• Rheumatoid arthritis—a condition where the immune system mistakenly attacks the cells that line the joints, making the joints stiff, swollen, and painful.

Can you live without a thymus gland?
 

It’s possible to live without a thymus. Sometimes, surgery is needed to remove the gland (thymectomy) to treat conditions such as thymic tumours and myasthenia gravis.

However, studies have linked the removal of the thymus in infants to an increased susceptibility to infection and autoimmune disorders [5].

How to check your hormone health
 

Want to check your hormone health and not sure which test is right for you? Our Male Hormone Blood Test Buying Guide and Female Hormone Blood Test Buying Guide are a good place to start.

You can find out more about hormones in our Hormone Health Hub.

References

1. Thapa, P., and Farber, D.L. (2019) The role of the thymus in the immune response.Thorac Surg Clin, 29(2):123-131. doi: 10.1016/j.thorsurg.2018.12.001
2. Li, Y.R., and Zúñiga-Pflücker, J.C. (2023) Thymus aging and immune reconstitution, progresses and challenges. Semin Immunol. 70:101837. doi:10.1016/j.smim.2023.101837
3. Cancer Research UK (2022) Thymus Gland Cancer. Available at: https://www.cancerresearchuk.org/about-cancer/thymus-gland-cancer#:~:text=Types%20of%20thymus%20gland%20cancer&text=These%20types%20of%20cancers%20develop,above%20the%20age%20of%2050. [Accessed 10 September 2024].
4. Kabir, A., Alizadehfar, R., and Tsoukas, C.M. (2022) Good's syndrome: time to move on from reviewing the past. Front Immunol, 12:815710. doi:10.3389/fimmu.2021.815710
5. Stosio, M., Ruszkowski, J., Mikosik-Roczyńska, A., Haponiuk, I., and Witkowski, J.M. (2017) The significance of neonatal thymectomy for shaping the immune system in children with congenital heart defects.Kardiochir Torakochirurgia Pol, 14(4):258–262. doi:10.5114/kitp.2017.72231