Infectious disease immunology has largely focused on the effector immune response (effector cells are relatively short-lived activated cells that defend the body in an immune response), changes in the blood and peripheral lymphoid organs of infected individuals, and vaccine development. Studies of the thymus in infected individuals have been neglected, although this is progressively changing likely due to the fact that depressed immunity and increased susceptibility to infection is plaguing our population.
The thymus gland is the primary lymphatic tissue located in the thorax behind the sternum. One, if it’s main functions, is to nurture the lymphocytes (WBCs which fight viral infection, etc). Its size is large at birth and starts to atrophy around the time of puberty. By “old age” the thymus has almost completely disappeared. At birth, the child benefits from the lymphocytes passed on to him by his mother, which protect the child from infections. He must quickly start to produce his/her own lymphocytes, which will mostly originate from bone marrow and thymus. A thymic deficiency in the newborn will result in lack of T-lymphocytes and in the quick appearance of physiological complications that will translate into slower growth rate or repetitive infections, and possibly lead to premature death.
Medical texts claim it is normal for the thymus to develop throughout childhood, and to atrophy in adults. But although the thymus is not as big or as active as it was when we were young, the smaller thymus is still able to help train T cells well into our eighties and beyond. However, many practitioners believe thymus atrophy is endemic rather than normal presenting the concept that when modern allopathic medicine attempts to overtake the responsibilities of a healthy immune system, the system stagnates and atrophies, becoming even less able to fulfil its responsibilities.
T-lymphocytes are derived from or influenced by thymus hormone. To become mature, all T-lymphocytes must reside in the thymus gland for a period of time. This cell in the thymus gland is called a thymocyte and acquires either CD4 or CD8 characteristics. Only those thymocytes expressing CD4 or CD8 characteristics are positively selected to emigrate, by way of the thymus gland, to the lymphatic system. This differentiation process results in mature lymphocytes that can T foreign bodies, viruses or cancerous cells, in the context of major histocompatible complex hormones. CD4 cells are known as “helper” cells because they “help” the immune system by recognizing foreign substances on contact. CD8 cells are called T-suppressor/cytotoxic or “killer” cells.
A variety of infectious agents including viral diseases such as AIDS, simian immunodeficiency syndrome, rabies, MG, bacterial infections, parasites and fungal infections target the thymus gland. This targeting has consequences on the behaviour of peripheral T lymphocytes. A common feature seen in a variety of acute infections is severe atrophy of the thymus. In this context, thymus-centred immuno-therapeutic approaches potentially represent a new tool for the treatment of severe infectious diseases.
The thymus gland and thymic hormones contribute to human immunity, the neuroendocrine system, the reproductive system, and the development of the central nervous system. Additionally, alteration in the status of the thyroid, adrenal and pituitary glands, as well as the kidney, have affected the structure and function of the thymus gland.