Organs of the Immune System: The Thymus

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Among organs that contribute to our immune response there are two categories: primary lymphoid organs and secondary lymphoid organs.

The thymus is one of two primary lymphoid organs, along with the bone marrow. It is a little two-lobed organ found above the heart.

The Job of the Thymus

The overarching function of the thymus is to select, develop and mature a repertoire of T cells that can then go out and protect the body from infection.

When the thymus isn't functioning, there is a dearth of T-cell lymphocytes circulating in the body, leading to an absence of so-called cell-mediated immunity, according to the sixth edition of Kuby's Immunology. The consequence is an increased risk of infection.

As we age, the thymus turns to fat and shrinks. Whereas it might weigh as much as 30 grams in babies, in the elderly it may weigh as little as 3 grams. If the thymus is functioning at 100 percent in babies, it is generally found to be operating at around 20 percent in our thirties and at as little as 2 percent by age 65.

The Thymus in Lymphoma

The diagnosis of thymic lymphoma (also known as primary mediastinal B-cell lymphoma) occurs when lymphocytes in the thymus turn cancerous.

When this happens, the disease is classified in one of two ways. If the cancer is in the cells that constitute the outer covering of the thymus, that is called thymoma or thymic carcinoma (carcinomas refer to cancers of epithelial cells in surrounding tissue, as opposed to connective tissue). If cancer develops from the lymphocytes in the thymus, it is thymic lymphoma.

Since the thymus is located in an area of the body referred to as the mediastinum, it is often called primary mediastinal lymphoma.

Thymic lymphoma is a very rare subtype of non-Hodgkin's lymphoma. It is an aggressive disease, and there is no consensus regarding optimal treatment. Perhaps the only consensus is that in order for there to be hope of beating the disease, treatment generally should begin as soon as possible following diagnosis.

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