The lymph system and lymphoid tissue

The lymph system and lymphoid tissue

To know what lymphoma is, it helps to understand the body's lymph system.

The lymph system (also known as the lymphatic system) is composed mainly of lymphoid tissue, lymph vessels, and a clear fluid called lymph. Lymphoid tissue includes the lymph nodes and related organs that are part of the body's immune and blood-forming systems, such as the spleen and bone marrow.

Lymphocytes

Lymphoid tissue is made up of several types of immune system cells that help the body fight infections. Most of the cells in lymphoid tissue are lymphocytes, a type of white blood cell. The 2 main types of lymphocytes are B lymphocytes (B cells) and T lymphocytes (T cells). Normal B cells and T cells do different jobs within the immune system.

B lymphocytes: B cells normally help protect the body against germs (bacteria or viruses) by making proteins called antibodies. The antibodies attach to the germs, marking them for destruction by other immune system cells. Antibodies also attract certain blood proteins that can kill bacteria.

T lymphocytes: There are several types of T cells, each with a special job. Some T cells can directly destroy cells infected with viruses, fungi, or certain kinds of bacteria. T cells can also release substances that attract other types of white blood cells, which then digest the infected cells. Some types of T cells play a role in either boosting or slowing the activity of other immune system cells.

Both types of lymphocytes can develop into lymphoma cells, but B-cell lymphomas are much more common in the United States than T-cell lymphomas. Different types of lymphoma can develop from each type of lymphocyte, based on how mature the cells are when they become cancerous and other factors.

Treatment for each lymphoma depends on which type it is, so determining the exact type of lymphoma is important.

Organs that have lymphoid tissue

Lymphoid tissue is found in many places throughout the body. Because lymphoid tissue is in many parts of the body, lymphomas can start almost anywhere. The major sites of lymphoid tissue are:

Lymph nodes: Lymph nodes are bean-sized organs found throughout the body, including inside the chest, abdomen, and pelvis. They can sometimes be felt under the skin in the neck, under the arms, and in the groin. Lymph nodes are made up mainly of lymphocytes.

The lymph nodes in the body are connected by a system of lymph vessels. These vessels are like veins, except that instead of carrying blood, they carry lymph and lymphocytes.

Lymph nodes get bigger when they fight infection. Lymph nodes that grow in reaction to infection are called reactive nodes or hyperplastic nodes and are often tender to the touch. An enlarged lymph node is not always a sign of a serious problem. People with sore throats or colds often feel enlarged lymph nodes in the neck. But a large lymph node is also the most common sign of lymphoma. Lymph node enlargement is discussed more in the section, "How is non-Hodgkin lymphoma diagnosed?"

Spleen: The spleen is an organ under the lower part of the rib cage on the left side of the body. An average adult spleen weighs about 5 ounces. The spleen makes lymphocytes and other immune system cells to help fight infection. It also stores healthy blood cells and filters out damaged blood cells, bacteria, and cell waste.

Thymus: The thymus is a small organ behind the upper part of the breastbone and in front of the heart. Before birth, the thymus plays a vital role in development of T lymphocytes. The thymus shrinks and becomes less important over the first 20 years of life. Despite this, it continues to play a role in immune system function.

Adenoids and tonsils: These are collections of lymphoid tissue at the back of the throat. They help make antibodies against germs that are breathed in or swallowed. They are easy to see when they become enlarged during an infection or if they become cancerous.

Digestive tract: The stomach and intestines as well as many other organs also have lymphoid tissue.

Bone marrow: The bone marrow (the soft inner part of certain bones) makes red blood cells, blood platelets, and white blood cells. Red blood cells carry oxygen from the lungs to the rest of the body. Platelets plug up small holes in blood vessels caused by cuts or scrapes. White blood cells' main job is fighting infections. The 2 main types of white blood cells are granulocytes and lymphocytes. Bone marrow lymphocytes are primarily B cells. Lymphomas sometimes start from bone marrow lymphocytes.

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