Lymphocytes are white blood cells and 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 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.

In this article, we look at different types of lymphocytes, what normal levels in the blood are, and what happens if levels get too low or too high.

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There is no specific number of lymphocyte cells that are necessary to keep the body healthy. This is because lymphocyte levels can change according to a person’s race, gender, location, and lifestyle habits.

However, keeping the number of lymphocytes circulating around the body within a healthy range is important for immune system functioning.

Some lymphocyte cells are responsible for attacking bacteria and viruses. Other lymphoctyes target the body’s own cells that are not functioning properly due to a virus or cancer. Having too many or too few lymphocytes can be a sign of disease.

The normal lymphocyte range in adults is between 1,000 and 4,800 lymphocytes in 1 microliter (µL) of blood. In children, the normal range is between 3,000 and 9,500 lymphocytes in 1 µL of blood.

Lymphocyte counts above the normal range can be a harmless and temporary situation, due to the body’s normal response to an infection or inflammatory condition.

Causes

A high level of lymphocytes can also be a sign of lymphocytosis, which may indicate a more serious condition. Doctors typically refer to lymphocyte counts of more than 4,000 per 1 µL of blood in adults as lymphocytosis. However, this threshold can vary between labs and people of different ages.

People with lymphocytosis may experience symptoms depending on what is causing this spike in lymphocytes. Some possible causes of lymphocytosis include:

A doctor may perform a variety of tests to diagnose the underlying cause of lymphocytosis. They will check an individual’s symptoms and medical history. Doctors may order additional diagnostic tests, such as blood tests or medical imaging scans, to confirm the cause.

How to lower levels

Lymphocyte levels may return to normal on their own or following treatment. Doctors will first identify the underlying cause of lymphocytosis to determine the best way of lowering lymphocyte levels.

For example, the Epstein-Barr virus (EPV) is one of the most common causes of abnormally high lymphocyte levels. The virus can cause mononucleosis (mono), and doctors may recommend over-the-counter pain medications and rest until symptoms improve.

Other possible causes may require medical treatment from a doctor. For example, some people may experience lymphocytosis as a result of cancer. Doctors may recommend a combination of approaches to treat cancer, such as chemotherapy and surgery.

Lymphocyte counts below the normal range can also be temporary.

Causes

Doctors refer to abnormally low lymphocyte numbers as lymphocytopenia. For adults, this is typically a count of less than 1,000 lymphocytes in 1 µL of blood. It can be a result of:

  • the body not making enough lymphocytes
  • a disease that destroys lymphocytes
  • lymphocytes getting stuck in the lymph nodes

Lymphocytopenia can occur following diseases or therapies that include:

In some cases, people can inherit lymphocytopenia. For example, people with Wiskott-Aldrich syndrome have genetic mutations that reduce the body’s capacity to produce lymphocytes.

How to raise levels

Doctors will not always recommend increasing lymphocytes. For example, people who have mild cases of lymphocytopenia without a clear cause may see the condition resolve on its own.

Treating the underlying condition can increase lymphocytes in other cases where the condition is clear. For example, doctors may prescribe antibiotics to treat a bacterial infection that could be causing abnormally low lymphocyte levels.

Some diseases may require long-term treatments to increase lymphocytes. For example, people with lupus may require a combination of medications to manage the condition. Managing the disease may increase lymphocytes to a normal level.

There are two categories of lymphocytes, known as B lymphocytes and T lymphocytes. People commonly refer to these as B cells and T cells.

Both types originate from stem cells in the bone marrow. From there, some cells travel to the thymus, where they become T cells. Others remain in the bone marrow, where they become B cells.

The job of B cells is to make antibodies, which are proteins produced by the immune system to fight foreign substances known as antigens.

Each B cell makes one specific antibody. Each antibody matches an antigen for destruction. The process of matching is similar to how a key fits into a lock.

The job of T cells is to help the body kill cancer cells and control the immune response to foreign substances. They do this by destroying cells in the body that have been taken over by viruses or become cancerous.

A third type of lymphocyte, known as a natural killer or NK cell, comes from the same place as B and T cells. NK cells respond quickly to several foreign substances and are specialized in killing cancer cells and virus-infected cells.

There are different types of B cells and T cells that have specific roles in the body and the immune system.

B cells

There are also several types of B cells:

Memory B cells

Memory B cells circulate in the body to start a fast antibody response when they find a foreign substance. They remain in the body for decades and become memory cells, which remember antigens and help the immune system respond faster to future attacks.

Regulatory B cells

Regulatory B cells, or Bregs, only account for a small number of B cells in healthy people. Although few in number, they have a vital role to play.

Bregs have protective anti-inflammatory effects in the body and stop lymphocytes that cause inflammation. They also interact with several other immune cells and promote the production of regulatory T cells, or Tregs.

Plasma cells

Plasma cells are terminally differentiated B cells that produce antibodies and are responsible for antibody-mediated immunity. Terminally differentiated cells are cells that become specialized to a point after which they can no longer divide.

T cells

There are several types of T cells:

Killer T cells

Killer, or cytotoxic, T cells scan the surface of cells in the body to see if they have become infected with germs or turned cancerous. If so, they kill these cells.

Helper T cells

Helper T cells “help” other cells in the immune system to start and control the immune response against foreign substances.

There are different types of helper T cells, and some are more effective than others against different types of germs.

Regulatory T cells, or Tregs

Tregs control or suppress other cells in the immune system. They have both helpful and harmful effects.

They maintain tolerance to germs, prevent autoimmune diseases, and limit inflammatory diseases. But they can also suppress the immune system from doing its job against certain antigens and tumors.

Memory T cells

Memory T cells protect the body against antigens that they have previously identified. They live for a long time after an infection is over, helping the immune system remember previous infections.

If the same germ enters the body a second time, memory T cells remember it and quickly multiply, helping the body fight it more quickly.

Natural killer T cells

Natural killer T cells are a mixed group of T cells that share characteristics of both T cells and natural killer cells. They can influence other immune cells and control immune responses against substances in the body that trigger an immune response.

Doctors refer to a blood test that counts how many lymphocytes are in the blood as a B and T cell screen. This test measures the levels of the main types of white blood cells in the body.

Lymphocyte count is one part of a complete blood count (CBC), which is a larger whole blood test. Doctors may request a CBC if they suspect that a disease or infection is present.

The test can also use a sample of the bone marrow instead of blood in some cases.

The B and T cell screen will give an estimate of the amount of T and B cells in the blood.

Results can indicate a normal cell count or an abnormal cell count, the latter pointing to the possible presence of a disease. In this case, the doctor will likely ask for other tests to confirm a diagnosis.

T cell counts above the normal range can indicate any of the following conditions:

B cell counts above the normal range can indicate:

T cell counts below the normal range can indicate:

  • a disease present from birth
  • an acquired T cell deficiency disease, such as HIV
  • a type of cancer
  • DiGeorge syndrome

B cell counts below the normal range can indicate:

Unusually high or low lymphocyte counts may cause no signs, symptoms, or serious problems on their own. They can be the body’s normal 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. These conditions can range from mild to severe, and how long they last depends on their cause.

Treatment for abnormal levels of lymphocytes will depend on both the cause and severity, and mild forms may not require any treatment at all.