**9. Effect of malfunctioning thymus gland on the body**

Thymus experiences atrophy with time which is triggered by numerous factors viz. growth and aging, infections and endocrine instabilities which give rise to a nonstandard liberation of T cells and consequently weakened the immunity [6]. The main organic task of this gland is to spawn a distinct T cells range to establish a crucial portion in host immunity counter to external pathogens, whereas the thymus correspondingly theaters a serious part in self-tolerance through negative assortment and the T reg cells formerly known as suppresser T cells production. Some of the thymic-derived malfunctionings are categorized bellow.

#### **9.1 Hypersensitivity/immunodeficiency or autoimmune disease**

When the immune system of body trigger against its own body cells and show the excessive action then the allergic condition developed [15]. Allergens are the substances which initiate the allergic response. IgE antibodies are more common in this condition. Histamine is also present in allergic condition which are released from the Mast cells. Anaphylaxis is a condition developed when these allergens cause an acute to severe reaction and that sometimes proves fatal condition. In this case, the immune system becomes hyperactive and cause the death of own host cells instead of killing foreign pathogens. Thymus parenchymal cells have the ability to recognition the body own cells and prevent them from killing central tolerance process that is immunologic tolerance to self-antigens. During such diseases, the demarcation between the cortex and the medulla deteriorated and the medullar epithelial cells are also dispersed [16]. A rare autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy is an inherited syndrome and is because of alterations in the specific gene [14]. Such gene permits the illustration of tissue related particular proteins present in the thymic medulla. This disease also affects multiple endocrine tissues. As T cell production take place in the thymus gland and if there is any defect in thymocyte development, it leads to profound decrease in the production of T cell, which may result into immunodeficiency disease. Abnormality to the thymic epithelial cells leads to the T cells dysfunctions, which may result in chronic inflammatory disease in the host [11, 12]. The tolerance is failed due to available antigens in the tissue is because of the autoimmune illnesses. If there is a defect in the production of both T cell and B cell, it results into severe combined immunodeficiency (SCID). When the combine deficiency of T lymphocytes and B lymphocytes occurs together, then the condition developed is known as SCID. This is a rare congenital disease, which is initiated by the non-functional hematopoietic progenitor cells that act as precursor of the B lymphocytes and T lymphocytes. When this condition develops, there is decrease in the lymphocytes production which results into the thymus atrophy [16]. There are also some other factors which are responsible for the causation of

**29**

*Microarchitecture of the Thymus Gland; Its Age and Disease-Associated Morphological…*

this disease such as IL-7 deficiency, recombination activating gene deficiency and common gamma chain deficiency. Another autoimmune disease in which the antibodies blocks the acetylcholine receptors at neuromuscular junction. This autoimmune disease is known as myasthenia gravis. This illness is categorized as softness and fatigability of the muscle and is triggered by autoantibodies depending T cell counter to the neuromuscular junction. Its exact cause is unknown; however, it is assumed that changes in the thymus and the thymic epithelial cells is one of the main causes of its pathogenesis [14, 15]. Sometimes, this disease is associated with thymic hyperplasia. This disease is commonly cured by the surgical amputation of the thymus which is known as thymectomy. The conditions like thymic hyperplasia or malignancy are nearly 70% more common in the patients suffering with such autoimmune disease. Type-1 diabetes is also an autoimmune-based disease, which results from the obliteration of cells in the islets of Langerhans. The pancreas infiltrating T lymphocytes cause the destruction of the insulin producing cells in the islets of Langerhans. The body, in this case, does not produce insulin. It is seemed to be more commonly present in adults. It has been observed that lack of immune tolerance to the cells present in the pancreas is the initial cause of such diabetes development. The Human immunodeficiency virus (HIV virus) effect the developing lymphocytes and results into killing of these cells [18]. When the lymphocytes decrease in the body, then the T cell immunodeficiency syndrome occurs, which are acquired in nature. The HIV virus usually cause the killing the CD4 T cells and it also mainly effect the mature T lymphocytes which are present at the periphery. In this case, a rapid atrophy of the thymus takes place in the

This inherited ailment is because of the obliteration of a minor piece of chromosome-22, which is one of 23 pair of human chromosomes [17]. The syndrome affects the individual through various means like cleft palate, facial defects, delay development, learning problems, and promote infections. As far as the immunity is concerned, this syndrome leads to inherited shortcomings containing thymic atrophy and aplasia. Such affected persons may have intense deficiency of T cell lineage. In this disease, the thymic parenchymal cells are lost and the area is then

Thymomas is a scarce neoplasia (benign in nature) arise from the thymic epithelial cells. In the thymoma patients, there are chances for the occurrence of a disease known as thymoma-associated multiorgan autoimmunity (TAMA). In these patients, the donor does not act like a basis of pathogenic T cells instead, the individual particular thymus gland yields the infected T cells which is directed toward its own body cells [19]. If the thymoma indicates the malignancy of the thymus gland, then its product is the defective T cells which are unable to recognize their own body cells as self-antigens. So that is why we can hardly distinguish this disease from GVHD. These types of tumors, usually 10–15%, are presented in the patients who are already suffering from myasthenia gravis. The symptoms include strong cough which sometimes get confused with bronchitis because the laryngeal nerve is compressed by the tumor. All thymomas are cancerous, but they are varied from each other in different aspects like some develop slowly and some tumors grow with the rapid rate and infect the surrounding tissue [20]. The treatment of this condition is the surgical removal of the infected part or whole gland.

*DOI: http://dx.doi.org/10.5772/intechopen.88480*

infected individual.

**9.2 DiGeorge syndrome**

replaced by the stromal CT.

**9.3 Tumors**

*Microarchitecture of the Thymus Gland; Its Age and Disease-Associated Morphological… DOI: http://dx.doi.org/10.5772/intechopen.88480*

this disease such as IL-7 deficiency, recombination activating gene deficiency and common gamma chain deficiency. Another autoimmune disease in which the antibodies blocks the acetylcholine receptors at neuromuscular junction. This autoimmune disease is known as myasthenia gravis. This illness is categorized as softness and fatigability of the muscle and is triggered by autoantibodies depending T cell counter to the neuromuscular junction. Its exact cause is unknown; however, it is assumed that changes in the thymus and the thymic epithelial cells is one of the main causes of its pathogenesis [14, 15]. Sometimes, this disease is associated with thymic hyperplasia. This disease is commonly cured by the surgical amputation of the thymus which is known as thymectomy. The conditions like thymic hyperplasia or malignancy are nearly 70% more common in the patients suffering with such autoimmune disease. Type-1 diabetes is also an autoimmune-based disease, which results from the obliteration of cells in the islets of Langerhans. The pancreas infiltrating T lymphocytes cause the destruction of the insulin producing cells in the islets of Langerhans. The body, in this case, does not produce insulin. It is seemed to be more commonly present in adults. It has been observed that lack of immune tolerance to the cells present in the pancreas is the initial cause of such diabetes development. The Human immunodeficiency virus (HIV virus) effect the developing lymphocytes and results into killing of these cells [18]. When the lymphocytes decrease in the body, then the T cell immunodeficiency syndrome occurs, which are acquired in nature. The HIV virus usually cause the killing the CD4 T cells and it also mainly effect the mature T lymphocytes which are present at the periphery. In this case, a rapid atrophy of the thymus takes place in the infected individual.

#### **9.2 DiGeorge syndrome**

This inherited ailment is because of the obliteration of a minor piece of chromosome-22, which is one of 23 pair of human chromosomes [17]. The syndrome affects the individual through various means like cleft palate, facial defects, delay development, learning problems, and promote infections. As far as the immunity is concerned, this syndrome leads to inherited shortcomings containing thymic atrophy and aplasia. Such affected persons may have intense deficiency of T cell lineage. In this disease, the thymic parenchymal cells are lost and the area is then replaced by the stromal CT.

#### **9.3 Tumors**

*Thymus*

**8. Effect of removal of the thymus gland and its clinical significance**

nantly due to complications with infection and lack of immunity.

**9. Effect of malfunctioning thymus gland on the body**

Some of the thymic-derived malfunctionings are categorized bellow.

**9.1 Hypersensitivity/immunodeficiency or autoimmune disease**

Thymus gland is an important component of immune system. This system defends the host from several infections [11]. It's inappropriate performance may produce embarrassment or even fatality. If the thymus gland is removed from the new borne individual, then there will be no possibility of the T cell production [6]. Other, lymphoid organs will also lack or decrease the number of T cell to fight against the pathogens. Consequently, death of the individual may occur, predomi-

Thymus experiences atrophy with time which is triggered by numerous factors viz. growth and aging, infections and endocrine instabilities which give rise to a nonstandard liberation of T cells and consequently weakened the immunity [6]. The main organic task of this gland is to spawn a distinct T cells range to establish a crucial portion in host immunity counter to external pathogens, whereas the thymus correspondingly theaters a serious part in self-tolerance through negative assortment and the T reg cells formerly known as suppresser T cells production.

When the immune system of body trigger against its own body cells and show the excessive action then the allergic condition developed [15]. Allergens are the substances which initiate the allergic response. IgE antibodies are more common in this condition. Histamine is also present in allergic condition which are released from the Mast cells. Anaphylaxis is a condition developed when these allergens cause an acute to severe reaction and that sometimes proves fatal condition. In this case, the immune system becomes hyperactive and cause the death of own host cells instead of killing foreign pathogens. Thymus parenchymal cells have the ability to recognition the body own cells and prevent them from killing central tolerance process that is immunologic tolerance to self-antigens. During such diseases, the demarcation between the cortex and the medulla deteriorated and the medullar epithelial cells are also dispersed [16]. A rare autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy is an inherited syndrome and is because of alterations in the specific gene [14]. Such gene permits the illustration of tissue related particular proteins present in the thymic medulla. This disease also affects multiple endocrine tissues. As T cell production take place in the thymus gland and if there is any defect in thymocyte development, it leads to profound decrease in the production of T cell, which may result into immunodeficiency disease. Abnormality to the thymic epithelial cells leads to the T cells dysfunctions, which may result in chronic inflammatory disease in the host [11, 12]. The tolerance is failed due to available antigens in the tissue is because of the autoimmune illnesses. If there is a defect in the production of both T cell and B cell, it results into severe combined immunodeficiency (SCID). When the combine deficiency of T lymphocytes and B lymphocytes occurs together, then the condition developed is known as SCID. This is a rare congenital disease, which is initiated by the non-functional hematopoietic progenitor cells that act as precursor of the B lymphocytes and T lymphocytes. When this condition develops, there is decrease in the lymphocytes production which results into the thymus atrophy [16]. There are also some other factors which are responsible for the causation of

**28**

Thymomas is a scarce neoplasia (benign in nature) arise from the thymic epithelial cells. In the thymoma patients, there are chances for the occurrence of a disease known as thymoma-associated multiorgan autoimmunity (TAMA). In these patients, the donor does not act like a basis of pathogenic T cells instead, the individual particular thymus gland yields the infected T cells which is directed toward its own body cells [19]. If the thymoma indicates the malignancy of the thymus gland, then its product is the defective T cells which are unable to recognize their own body cells as self-antigens. So that is why we can hardly distinguish this disease from GVHD. These types of tumors, usually 10–15%, are presented in the patients who are already suffering from myasthenia gravis. The symptoms include strong cough which sometimes get confused with bronchitis because the laryngeal nerve is compressed by the tumor. All thymomas are cancerous, but they are varied from each other in different aspects like some develop slowly and some tumors grow with the rapid rate and infect the surrounding tissue [20]. The treatment of this condition is the surgical removal of the infected part or whole gland.

Thymic lymphomas are tumors which originate from the thymocytes of the thymus gland. These lymphomas or leukemia acts like the precursors of the origin of the thymocyte are often classified as T acute lymphoblastic leukemia/lymphoma. Before 1950, the radiation was used to cure the people who are suffering from the enlarged thymus gland particularly the children. The post-operative complication in the treated people includes an elevated incidence of thyroid cancer and leukemia. The rare malformation of thymus gland includes the cervical thymus cyst which is something confusing with the tumors. In the literature, there is no as such detail study of the thymic cyst prevalence. There is no such common lesion appeared which are present in this condition. In the childhood, there are more chances of the thymic cyst and the ectopic cervical thymus than the adults.
