Thymus: Location, Function, and Importance for the Immune System — Especially in Children

The thymus is one of the most important — and at the same time least well-known — organs of the immune system. Particularly in the first years of life, it performs functions that are fundamental for later immune defence. Although its activity declines significantly in adulthood, its importance remains considerable.

Among other things, this article discusses the functions of the thymus and the factors that influence them.

Where Is the Thymus Located and What Is Its Function in the Body?

The thymus is a primary lymphatic organ located in the anterior upper chest. It lies behind the sternum, in front of the heart and between the lungs (Gray’s Anatomy, 2020).

The central function of the thymus is the maturation and selection of T lymphocytes. In this organ, immune cells are trained to recognise foreign structures, while those that could attack the body’s own tissues are eliminated. This process is crucial for immunological self-tolerance. Although only a portion of the T cells produced in the thymus later enter the bloodstream, these cells play a key role in the targeted regulation of the immune response (Miller, 1961; Klein et al., 2014).

These processes take place unnoticed, which is why the thymus receives very little attention. However, its particular importance lies in the fact that it is primarily active in early life. During this period, a large part of the T-cell repertoire is established, which is crucial for later defence against infections. Disruptions during this developmental phase can impair the formation of the immune system and may be associated with increased susceptibility to infections (Palmer, 2013). In some cases, thymus transplantation may be possible or necessary; in others, consistent infection prophylaxis through hygiene measures or medication may be required (Markert et al., 1999).

Why Does the Importance of the Thymus Decline in Adulthood?

The thymus undergoes a physiological regression known as thymic involution. This process begins as early as puberty and leads to a decline in the production of new T cells over the course of life (Savino et al., 2007).

However, this does not mean that the thymus becomes irrelevant. Rather, it has already completed its most important developmental work by then.

Which Diseases Can Affect the Thymus?

The thymus can be directly or indirectly affected by various diseases, for example:

·       thymomas

·       thymic carcinomas

These tumours occur predominantly in adulthood and are often associated with immunological abnormalities such as autoimmune diseases (Detterbeck & Parsons, 2004). They are often treated surgically or with chemotherapy or radiotherapy. We will return to why this approach is not without downsides.

·       Autoimmune diseases such as myasthenia gravis

The thymus is closely linked to the regulation of self-tolerance. If this process is disrupted, autoreactive T cells may develop that attack the body’s own structures. Myasthenia gravis is usually treated with immunosuppressive drugs, such as corticosteroids (Gilhus, 2016).

Which Factors Influence Thymus Function?

Factors associated with changes in thymic function include in particular:

·       malnutrition

·       infections

 as well as

       ·       chemotherapy

·       radiotherapy

These interventions can not only eliminate tumour tissue but also damage the thymus — creating something of a vicious circle (see above).

Conclusion: A Small Organ with Great Importance

The thymus is fundamentally important for the development of the immune system, especially in childhood: it helps determine how reliably the body distinguishes between foreign and self.

Adequate nutrient intake and the avoidance of severe systemic stress — such as radiotherapy or chemotherapy, but also chronic inflammation or infectious diseases — are therefore desirable to support the proper function of this organ.

FAQ – Frequently Asked Questions About the Thymus

1. Which autoimmune diseases, besides myasthenia gravis, can result from thymus alterations?

These include conditions such as Good syndrome (a combination of thymoma and immunodeficiency), autoimmune cytopenias, and more rarely systemic diseases such as lupus erythematosus or rheumatoid arthritis (Gilhus, 2016; Detterbeck & Parsons, 2004).

2. Are thymus tumours common?

Thymomas and thymic carcinomas are medically relevant but rare.

3. Can one live without a thymus?

As described, impaired function or complete absence of the thymus in childhood is associated with significant consequences, whereas in adulthood the impact is considerably less severe.

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Sources:

·       Gray, H.; Standring, S. (eds.): “Gray’s Anatomy: The Anatomical Basis of Clinical Practice”, 42nd Edition, Elsevier, 2020.

·       Miller, J. F. A. P. (1961): “Immunological Function of the Thymus”, The Lancet.

·       Klein, L. et al. (2014): “Positive and negative selection of the T cell repertoire: what thymocytes see (and don’t see)”, Nature Reviews Immunology.

·       Palmer, D. B. (2013): “The Effect of Age on Thymic Function”, Frontiers in Immunology.

·       Markert, M. L. et al. (1999): “Transplantation of Thymus Tissue in Complete DiGeorge Syndrome”, New England Journal of Medicine.

·       Savino, W. et al. (2007): “The Thymus is a Common Target in Malnutrition and Infection”, British Journal of Nutrition.

·       Detterbeck, F. C.; Parsons, A. M. (2004): “Thymic Tumors”, Annals of Thoracic Surgery.

·       Gilhus, N. E. (2016): “Myasthenia Gravis”, New England Journal of Medicine.