Download PDF. Aging is an inevitable, progressive and irreversible process that is manifested with multiple organ dysfunction. Reactive oxygen species ROS is considered the main etiological factor of aging. The thymus gland is the primary site of T cell production and it represents a key organ of the immune system.
It is endodermal in origin and lies in the anterior mediastinum behind the sternum. Deterioration of the immune system with aging contributes to increased incidence of infection, autoimmunity, and cancer, thus increasing the rates of morbidity and mortality in elderly humans.
Aging is a multifactorial physiological condition that includes a progressive decline of organ function. It is accompanied with increased vulnerability to infections, immune disorders and neoplasms, and ultimately death. Imbalance between oxidants like free oxygen radicles reactive oxygen species, ROS and antioxidants is considered as an important etiology of aging.
Inside the mitochondria, oxidative stress liberates excessive ROS that induces more mitochondrial damage and more ROS, and the cycle repeats itself. Thymus is the primary cell donor for the lymphatic system, like the bone marrow which is the cell donor for the hemopoietic system. It manufactures the immunocompetent T cells.
Within the thymus the progenitor cells are created, then maturated and differentiated into mature T cells. The thymus gland is one of the contents of the anterior mediastinum as it lies behind the sternum but in front of the pericardium and heart. It is formed of two identical lobes; each lobe has a central medulla and a peripheral cortex. It develops from the third endodermal pharyngeal branchial pouch. The thymus is the largest and most active in neonates and pre-adolescents, afterwards it gradually involutes and ultimately disappears to be replaced by fat in elderly when it weighs 5g.
In congenital absence of thymus DiGeorge Syndrome there is deficiency of T cell immunity. Thymic involution refers to the process of multiple sessions of age-related atrophy and redevelopment before the incidence of complete thymic degeneration. Several authors relate the early involution of the thymus to an innate aging program while others attribute its incidence in early puberty to a developmental program that decelerates the growth rate.
Changes in thymus weight with age and during pregnancy were investigated in mice. In female mice thymus weight was markedly reduced by pregnancy and involution started 50 days after birth. MicroRNAs miRNAs may be considered as potential biomarkers for the study of sex- and age-related differences in involution of the thymus.
In these animals, there were age-related increases in the fibronectin content in the thymic capsule, the interlobular connective tissue, the perivascular tissue, and in the medulla and cortex.
Properly functioning thymus is the needed for reduction of morbidity and mortality rates in infections and transplantations. This led to the conclusion that maternal protein restriction during lactation slows aging of the immune system and prolongs the life span. The two glands form a functional complementary unit that maintains the immune and endocrine systems during aging.
The pineal gland is supposed to be responsible for involution of the thymus and control of its lifespan- determining function. Adult mice injected with embryonic thymic calf extracts ETCE , there was a fall in the level of cerebral and splenic unsaturated fatty acid peroxides. Histologically, thymus, liver and spleen of these injected animals resembled those of neonatal mice. In individuals treated with ETCE, presbyopia and climacteric symptoms disappeared. Thymuses, obtained from old mice and grafted into thymectomized young adult mice, could partially restore the circulating FTS level.
On the other hand, newborn thymuses could not sufficiently restore the serum FTS level when grafted in old thymectomized mice. Whether age-associated cataract in dogs could be cured or not, using thymus calf extract, remains a question for further studies.
On the contrary, the rate of protein synthesis diminished rapidly during involution, and continued to decrease at a slower rate during aging. The thymus is thought to be indulged in the pathogenesis of myasthenia gravis MG in patients with anti-acetylcholine receptor autoantibodies.
Thymectomy is widely used as a treatment of EOMG. Dysregulation of T-cell function plays an essential role in age-related decline of the immune system. Since T-lymphocytes mature during their journey through the thymus, and this gland shows an age-related atrophy, thymic regression has been considered as the triggering event of this immune deterioration in elderly people. These toxic molecules, which form in cells as a natural byproduct of the metabolism of oxygen, have been linked to progressive atrophy in many organs and tissues as part of the normal aging process.
However, these are generally slow, progressive processes that do not become apparent until late in life and often go mostly unnoticed. In future studies, the researchers will investigate whether antioxidant supplementation improves the functioning of the thymus and the immune system during aging. If these studies provide support for this idea, then they could lead to the development of new clinical recommendations for the prevention or treatment of age-related thymus atrophy in humans.
Materials provided by Cell Press. Note: Content may be edited for style and length. Science News. Story Source: Materials provided by Cell Press. Journal Reference : Griffith et al. Metabolic damage and premature thymus aging caused by stromal catalase deficiency. The thymus is a vital yet unusual organ.
Vital in that it is responsible for producing immune cells; unusual in that it is largest at childhood and progressively shrinks after puberty. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. The thymus gland is the body organ that took scientists the longest time to understand. It's only active from when you're born until you become a teenager. Still, it plays a huge role in training your body to fight infections and even cancer for the rest of your life.
It's also vital to the body's chemical messaging or endocrine system. Read on to learn more about the role of the thymus in immunity, autoimmunity, and aging, as well as how several disorders may affect this important organ.
The thymus gland is usually located behind the breastbone, in front of the heart, and between the lungs. In some people, though, this organ is found in the neck or upper chest. While that may seem odd, it's part of the organ's mystery that has baffled scientists for centuries. Researchers only began to understand some of the gland's function about 50 years ago.
They still aren't sure where it got its name. Some experts say the ancient Greeks, who discovered the organ, named it thymus because its shape looks like the leaves of thyme, a cooking herb. Others say the name came from the Greek word for the soul because the organ is near the heart. Either way, the thymus gland is considered an immune system organ.
Like your tonsils and adenoids, it helps fight infections. Unlike your heart or lungs, what the thymus gland does isn't apparent. Its job involves a lot of tiny chemical processes. Inside the thymus gland, there are many different cells. These include:. This list hints at how complex the thymus gland's job is. Its role also changes throughout your life. The famous Greek philosopher-surgeon, Galen, was the first to notice that the thymus gland changes with age.
Galen wrote that it's large in newborn animals and becomes smaller when they're adults. Your thymus gland reaches its maximum size when you're a teenager. Then, it starts to shrink slowly. By the time you turn 75 years old, your thymus gland turns to fat. The term scientists use to describe this organ shrinking process is called involution.
Doctors also know that severe stress can cause the thymus to shrink. In fact, during the early part of the 20th century, researchers didn't believe the thymus was larger in infants. When they did autopsies on babies who had died from conditions like diphtheria, it had shrunk. From the time you're conceived until you reach puberty, your thymus gland is very active.
It serves both the immune and endocrine systems. That's the system that makes hormones, the body's chemical messengers. To understand the thymus' immune system role, you need to know the difference between two kinds of white blood cells.
They are the T lymphocytes T-cells and B lymphocytes B-cells. These cells are like the immune system's "special ops" forces.
T-cells are also known as thymus-derived lymphocytes. They help fight off the body's foreign invaders, such as bacteria, viruses, and toxins. They can also identify and attack cancer cells. B lymphocytes, or B-cells, have a different role. They produce proteins called antibodies and use them to destroy specific invaders. When the immune system's first responders and defenders need extra help, they call in the T-cells. They're made in the bone marrow, the spongy tissue within your bones.
When T-cells are young or immature, they travel through the bloodstream and into the thymus gland. The thymus has two lobes. One houses a sort of "boot camp" training ground for T-cells. That's where they mature and turn into specialty disease-fighting cells with different jobs. T-cells in the thymus turn into three main immune system disease fighters:. The part of the thymus called the cortex is where the T-cell boot camp training is held. Here, young T-cells learn to identify antigens or toxins linked to foreign cells and matter.
This process is called "positive selection. Once the T-cells recognize specific pathogens, they travel to another part of the thymus gland called the medulla. Here, they get a different kind of training, "negative selection. This prevents autoimmune disorders. These are medical conditions where things go wrong, and your cells attack your body tissues and cells instead of foreign invaders.
Not all T-cells make it through this selection process. Next, the survivors get exposed to hormones produced by the thymus gland to complete their training.
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