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What Are Lymphocytes?

Lymphocytes are white blood cells that are one of the body's main types of immune cells. They are made in the bone marrow and found in the blood and lymph tissue. The immune system is a very complex network of cells known as immune cells that include lymphocytes. These cells work together to defend the body against foreign substances, such as bacteria, viruses, and cancer cells that can threaten its functioning. Here are different types of lymphocytes, what normal levels to have in the blood are, and what happens if levels get too low or too high.

Lymphocytes and how they work

Your bone marrow produces cells that will become lymphocytes. Some will enter your bloodstream, but most will move through your lymphatic system. The lymphatic system is the group of tissues and organs, like the spleen, tonsils, and lymph nodes that protect your body from infections.

About 25 percent of the new lymphocytes remain in the bone marrow and become B cells. The other 75 percent travel to your thymus and become T cells.

There are different kinds of B cells and T cells. These include:

  • effector cells that are activated by antigens to fight an active infection
  • memory cells that have been in your body long enough to recognize and “remember” past infections and go into action quickly if you become re-infected with an antigen
  • B lymphocytes and T lymphocytes work together to fight infection.


There are two major types of Lymphocytes:

  • B-Lymphocytes
  • T-Lymphocytes

B-Lymphocytes develop into unique cells, called Plasma Cells, that create precise proteins, called antibodies. These antibodies travel in the blood and react to infections, toxins, some bacteria, and also specific types of cancer cells. These antibodies act like biological guided missiles that seek out cells with a particular antigen on their surface. The body then recognizes and eliminates these unwanted invaders.

However, some of these problematic cells such as viruses can dodge B-Lymphocytes by growing within the body’s individual cells. T-Lymphocytes can sense when these cells have become infected and annihilate them immediately. T-Lymphocytes can also assist the body to beat viral infections and wipe out unusual or cancerous cells.

What causes a low lymphocyte count?

A low lymphocyte count, called lymphocytopenia, usually occurs because:

  • your body isn’t producing enough lymphocytes
  • lymphocytes are being destroyed
  • lymphocytes are trapped in your spleen or lymph nodes

What causes a high lymphocyte count?

Lymphocytosis is common if you’ve had an infection. High lymphocyte levels that persist may point to a more serious illness or disease, such as:

What is a B and T cell screen?

A blood test that counts how many lymphocytes are in a person's blood is called a B and T cell screen. In this test, the levels of the main types of white blood cells in the body are measured. Lymphocyte count is one part of a larger whole blood test called a complete blood count (CBC). A CBC can be requested by doctors if they suspect that a disease or infection is present.

Unusually high or low lymphocyte counts may cause no signs, symptoms, or serious problems on their own. They can be the body's response to an infection, inflammatory condition, or other unusual condition, and will return to normal levels after some time. If lymphocyte counts remain high or low over time, they could be a sign of a health condition and may be diagnosed as lymphocytopenia or lymphocytosis. These conditions can range from mild to severe, and their duration depends on what caused them. Treatment for abnormal levels of lymphocytes will depend on the cause and severity and mild forms may not require any at all.