If the thymus of an experimental animal is removed immediately after its birth, the animal exhibits thefollowing characteristics: (a) It is more susceptible to bacterial infections, (b) it has a decreased number oflymphocytes in lymphatic tissue, and (c) its ability to reject a graft is greatly decreased. Using your knowledgeof immunology explain each one of these observatio

Explanation:

Normally T cells are processed in the thymus and then migrate to other lymphatic tissues. Without the thymus, this processing is prevented. Because there are normally five T cells to every one B cell, the number of lymphocytes is greatly reduced. The loss of T cells results in an increased susceptibility to infections and an inability to reject grafts because of the loss of cell mediated immunity.

In addition, since helper T cells are involved with the activation of Bcells, antibody- mediated immunity is also depressed.

The thymus is a bilobed gland located in the superior mediastinum, the partition dividing the thoracic cavity into the left and right parts. The thymus increases in size until the first year of life, after which it remains approximately the same size until 60 years of age, when it decreases in size. The thymus is the site for the maturation of T cells.

Thymosin, a hormone secreted by the thymus, is important in the T-cell maturation process. Large numbers of lymphocytes are produced in the thymus, but most degenerate. The lymphocytes that survive the maturation process are capable of reacting to foreign substances, but they normally do not react to and destroy healthy body cells .These surviving thymic lymphocytes migrate to the medulla, enter the blood, and travel to other lymphatic tissues.

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