Medically reviewed by Stacy Sampson, D.O. — By Susan York Morris — Updated on September 28, 2018 Overview Lymphocytes are one of several different types of white blood cells. Each type of white blood cell has a specific function, and they all work together to fight illness and disease. White blood cells are an important part of your immune system. They help your body fight antigens, which are bacteria, viruses, and other toxins that make you sick. If your doctor says you have a weakened immune system, that means there aren’t enough white blood cells in your bloodstream (1). Your bone marrow constantly 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 infection (1). 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 (2). There are different kinds of B cells and T cells. These include:
B lymphocytes and T lymphocytes work together to fight infection. B lymphocytes recognize antigens and become plasma cells that produce antibodies to fight them. There are three types of T lymphocytes, and each plays its own role. These include:
Cytotoxic T cells, often called killer T cells, destroy cells in your body that have been infected with an antigen, cancer cells, and foreign cells like transplanted organs. Helper T cells direct the immune response of B cells and other T cells (2). Regulatory T cells suppress your immune system to keep its response in check. In addition to preventing autoimmune disease, they also prevent other white blood cells from fighting real or perceived antigens. Perceived antigens include substances like allergens and normal flora bacteria in the gastrointestinal tract. Allergens are things that cause an allergic reaction, which could include pollen, molds, or pet dander (1, 2). If you show symptoms of an infection and suspected blood disorder your overall lymphocyte count is abnormal. If this is the case, your doctor may order a blood test called a B and T cell screen to count how many lymphocytes are in your bloodstream. Lymphocyte counts that are too high or too low can be a sign of illness. Learn more: B and T cell screen » For the test, blood is drawn from your arm at your doctor’s office or a lab. The blood is then sent to a laboratory where it will be analyzed. The results will be sent to your doctor. Ask your doctor when you should expect the results. Depending on the lab, wait times can vary, but typically take no more than two to three days. There are a few things that can affect the results of your blood test. Tell your doctor if any of the following apply to you: Laboratories often have different ways of measuring blood test results. Results also vary by:
The following table gives approximate ranges for adults, but you’ll want to talk to your doctor about your results. Some factors could determine what’s a normal range for you. A low lymphocyte count, called lymphocytopenia, usually occurs because:
Lymphocytopenia can point to a number of conditions and diseases. Some, like the flu or mild infections, aren’t serious for most people. But a low lymphocyte count puts you at greater risk of infection. Other conditions that can cause lymphocytopenia include: You may find it helpful to ask the following questions if your doctor orders a B and T cell screen:
Lymphocyte counts that are either too low or too high may mean you have an infection or mild illness. When you recover, your lymphocyte levels will return to normal. If abnormal lymphocyte counts persist, your outlook depends on the underlying condition. Last medically reviewed on January 30, 2017 Healthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.
Lymphocytes are a type of white blood cell that plays a central role in your immune system by helping your body fight infection and disease. There are two types of lymphocytes called T cells and B cells. This article reviews five key facts about lymphocytes, including where they are found, what they look like, how the two types differ, how lymphocyte counts are measured, and how test results are interpreted. Like all blood cells, lymphocytes begin their life’s journey in the bone marrow. This is the spongy, soft tissue located in the center of your bones. Once lymphocytes are formed, they travel to and perform various functions within the lymphatic system. The lymphatic system is an open network of vessels, organs, and tissues that work together to protect the body from foreign invaders, maintain body fluid levels, and remove cellular waste. Lymphocytes travel throughout the lymphatic system in a fluid called lymph. Along the network of lymphatic vessels are clusters of small, bean-shaped organs called lymph nodes.
Lymph nodes are responsible for filtering lymph so that bacteria, viruses, parasites, fungi, and other invaders can be isolated and neutralized by lymphocytes. Lymph nodes contain the highest concentration of lymphocytes.
Besides your lymph nodes, lymphocytes are also found in lymphoid tissues and organs throughout the body, including your spleen, tonsils, and the lining of your airways. There are two main kinds of lymphocytes, called B cells and T cells. They perform different functions in the immune system to protect your body from infection. There are also subcategories of B cells and T cells that contribute to both your innate immunity (the generalized immune response you are born with) and your adaptive immunity (the disease-specific immune response that develops whenever you are exposed to a foreign invader). B cell lymphocytes are involved in adaptive, antibody-driven immunity. Antibodies are proteins produced by the immune system that are specific to each foreign invader your body encounters. They "recognize" the invader by a protein on its surface, called an antigen. Antibody-driven immunity is a tailored response that can more effectively fight infection. B cells don't kill foreign invaders themselves. Instead, they release antibodies that attach to the antigen of the invader. By doing so, it "tags" the invader for destruction by other immune cells.
B cells are produced in the bone marrow, where they mature and specialize into different types of B cells. They then travel to the spleen and lymph nodes to help fight infection. There are two main types of B cells, each of which has a specific function:
T cell lymphocytes are mainly involved in adaptive, cell-mediated immunity. This is a type of immunity that does not involve antibodies but instead directly targets and/or kills foreign cells. In essence, it wages cell-to-cell combat. T cells travel from your bone marrow to a small gland located behind the breastbone called the thymus. It is there that they begin to mature and specialize into different types of T cells. The different types of T cells have different functions:
Lymphocytes are not visible to the naked eye. They can be seen when a drop of blood is smeared onto a slide, treated with the right stains, and placed under the lens of a microscope. When examined under a microscope, lymphocytes will be bigger than red blood cells but fewer in numbers. Lymphocytes constitute around 20% and 40% of all white blood cells. Lymphocytes are round and are almost entirely composed of a nucleus (the core of a cell that contains its genetic material in the form of DNA). With the proper staining, the nucleus of a lymphocyte is dark purple, while the surrounding jelly-like fluid (called the cytoplasm) is a lighter pink. Blood tests are routinely performed whenever you have signs of an infection and other illnesses. These include tests that measure how many lymphocytes you have in your blood. The tests are easy to perform and only require a simple blood draw, typically from a vein in your arm. On blood test your healthcare provider may order is a complete blood found with differential (CBC w/ diff). This test is able to reveal the percentage of each type of white blood cell in your blood, including lymphocytes. The CBC w/ diff can also measure the number of red blood cells (which transport oxygen through the body), platelets (which are responsible for blood clotting), and hemoglobin (which carry oxygen molecules on red blood cells) in a sample of blood. A more advanced test called flow cytometry can identify and count the individual cells in your blood, including lymphocytes. With flow cytometry, your blood is suspended in a fluid and passed through a laser-generating instrument. The light produced from the laser scatters the cells in such a way that the cells can be individually counted and analyzed.
A normal lymphocyte count varies your age. For healthy adults, the range is between 1,000 and 4,800 cells per microliter of blood (cells/mL). For children, the range is between 3,000 and 9,500 cells/mL. A test called the B and T cell screen specifically counts B cells and T cells in a sample of blood. Also known as a B cell or T cell count, the test involves flow cytometry and can provide specific information about how well your immune system is functioning.
The test can also hone in on specific types of B cells and T cells. One such example is a CD4 count that measures the number of CD4 T cells that HIV targets for infection. A decrease in the number CD4 T cells in people with HIV is a sign that the disease is progressing. Having too many lymphocytes in your blood is called lymphocytosis, while having too few lymphocytes is called lymphopenia. Both are causes of concern and can arise from infections, diseases, and even certain medical treatments. Certain diseases can cause both lymphocytosis and lymphocytopenia. For instance, an infection will typically cause lymphocyte counts to increase, but recurrent or severe infections may also cause lymphocyte numbers to plummet. In other instances, a disease may cause one type of lymphocyte to increase and another type to drop. Lymphocytosis is an indication that the immune system has been activated in response to a disease or medical condition. It may be an indication of an infection or a cancer of the blood or lymphatic system, among other things.
Possible causes of lymphocytosis include: Lymphopenia is an indication that lymphocytes are either being depleted or are not being produced in ample quantities. This may be due to autoimmune diseases, infections, or certain medical treatments. Rare genetic disorders may also interfere with the normal production of lymphocytes.
Possible causes of lymphopenia include: Lymphocytes are a type of white blood cell. They are produced in the bone marrow and move throughout the lymphatic system to help fight infection and diseases. They include B cells that produce antibodies that "tag" foreign invaders for destruction and T cells that directly target and kill foreign invaders. A normal lymphocyte count varies by your age. Having too many or too few lymphocytes may be the sign of an infection, autoimmune disease, genetic disorder, or cancer. Certain medical treatments can also affect lymphocyte counts. These days, it is common for people to get their blood test results online before their healthcare providers. If you get your results and see that your lymphocytes are either high or low, don't panic. On their own, these blood tests only hint at what is going on in your body. They are not diagnostic of any medical condition. A drop or increase may indicate a serious condition, but it could also mean nothing. It is only when the values are compared to other test results that possible causes can be explored. If you see your lymphocytes are either high or low, ask your healthcare provider why. And, make an effort to understand what the other results mean as well. Frequently Asked Questions
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