What Are Lymphocytes?

nurse collecting sample of lymphocytes

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Lymphocytes are white blood cells that your bone marrow produces to help regulate your immune system. Your lymphocytes are found in the blood, lymph nodes, spleen, and tonsils—and there are three types: B cells, T cells, and natural killer (NK) cells.

The function of lymphocytes is to recognize and respond to infectious pathogens (harmful organisms and cells), such as bacteria and viruses. Once these pathogens are identified, lymphocytes help create an immune response that helps eliminate harmful cells from your body.


Lymphocytes are a key component of your immune system and help your body protect against infections and illness. The primary function of lymphocytes is to recognize and respond to pathogens and other harmful cells that cause infection. Examples of pathogens include bacteria, viruses, and fungi. Your lymphocytes can also help your body fight cancer.

Some lymphocytes can act as the immune system’s memory. Once you come into contact with a known pathogen, these lymphocytes will recognize it and quickly respond by attacking it so you don’t become infected by the same illness again. For example, when you get chickenpox, you usually won’t get them again thanks to your lymphocytes. This is also why vaccines help protect against certain diseases. 


The three main types of lymphocytes include B cells, T cells, and natural killer (NK) cells. Each type has its own unique function in the immune system to protect you from infections and diseases.

B Cell Lymphocytes

B cells develop and mature in the bone marrow and are found in your spleen, tonsils, and lymph nodes. B cells help your immune system recognize and fight pathogens you have previously encountered. There are two main types of B cells, each with a specific function:

  • Plasma cells: Produce antibodies (or, proteins in your blood that help fight infections) that attach to and destroy harmful cells.
  • Memory B cells: Act as your immune system’s memory bank, which can recognize pathogens you’ve previously encountered to launch a new attack if you are exposed again in the future. For example, if you’ve received a measles vaccination, B cells produce antibodies to protect you against a measles infection, even if you come into contact with someone who has measles.

T Cell Lymphocytes

T cells develop in the bone marrow and mature in the thymus (a small lymphoid organ under your breastbone). There are several different types of T cells, each with a unique function:

  • Cytotoxic T cells: Responsible for directly targeting and destroying pathogens (e.g., bacteria, viruses), infections, and certain cancer cells. 
  • Helper T cells: Activate and coordinate other immune system cells and help create an effective response against a pathogen.
  • Regulatory T cells: Help prevent the immune system from accidentally attacking the body’s healthy tissues when fighting an infection.

Natural Killer (NK) Cells

Natural killer (NK) cells can recognize and destroy infected or cancerous cells. NK cells develop in the bone marrow, liver, and thymus and are a part of your body’s innate immune system. These cells help kill viruses and can also detect and destroy cancer cells.

Normal Lymphocyte Count

A lymphocyte count measures the number of lymphocytes (white blood cells) in your blood. A complete blood count (CBC) test can determine your lymphocyte count and other measurements of your blood. Because lymphocytes play a key role in your immune system, a change in your lymphocyte count may suggest underlying health conditions. 

Generally, between 20% to 40% of your white blood cells are lymphocytes. The normal lymphocyte count range varies depending on your age and overall health. In healthy adults, a normal lymphocyte count ranges from 1,000 to 4,800 per microliter of blood. Young children usually have higher lymphocyte counts, with normal ranges between 3,000 to 9,500 per microliter of blood.

Several factors can affect your lymphocyte count, including:

  • Age: Young children tend to have higher lymphocyte counts than adults 
  • Health conditions: Living with certain infections, autoimmune disorders, and cancer can change lymphocyte counts 
  • Certain medications: Taking certain medications such as chemotherapy drugs can alter your lymphocyte count

What Does A Low Lymphocyte Count Mean?

A low lymphocyte count (lymphopenia) means that the number of lymphocytes in your blood is lower than average. This often occurs due to depletion—meaning, your body is not producing enough white blood cells to maintain a strong immune system. Lymphopenia can make you more susceptible to infections and may be a sign of other health issues.

Many factors can cause low lymphocyte counts, including:

  • Poor nutrition 
  • Excessive alcohol consumption
  • Infections such as HIV, COVID-19, tuberculosis, or pneumonia
  • Certain medications, such as immunosuppressants and chemotherapy drugs
  • Autoimmune disorders, such as lupus, rheumatoid arthritis, and Sjogren’s syndrome
  • Radiation therapy
  • Blood diseases, such as aplastic anemia and Hodgkin’s disease

What Does A High Lymphocyte Count Mean?

A high lymphocyte count (lymphocytosis) means that you have more lymphocytes in your blood than normal. Lymphocytosis can indicate that your immune system is activated to fight an infection or underlying medical condition, such as:

How To Treat an Abnormal Lymphocyte Count

If your lymphocyte count is abnormally low or high, treatment to boost or lower your lymphocyte count will depend on the underlying cause.

A diet rich in protein and vegetables can help stimulate lymphocyte production and support your immune system if your lymphocyte count is low. For example, fatty fish (e.g., salmon), nuts, leafy green vegetables, yogurt, berries, and lean proteins (e.g., chicken) are all foods that can help your body build white blood cells.

If an infection or medical condition is causing an abnormal lymphocyte count, treating the underlying cause is essential for restoring lymphocytes to a normal level. Treatment varies, depending on the cause:

  • Infections: Chronic viral infections (e.g., HIV) may be treated with antiviral medications to help manage symptoms, while bacterial infections are usually treated with antibiotics. 
  • Medications: If a medication is causing your low lymphocyte count, your healthcare provider may adjust the dosage of your medicine or recommend a different drug that limits changes to your lymphocyte count.
  • Autoimmune disorders: Immunosuppressant medications can help reduce symptoms of autoimmune disorders. 
  • Cancer: Chemotherapy and radiation therapy are standard treatments for killing cancerous cells. 

In some cases, your healthcare provider may prescribe gamma globulin (a substance made from blood plasma) to boost the number of lymphocytes in your bloodstream and protect you from infection. Healthcare providers can also recommend stem cell transplants for people with chronic lymphopenia to restore lymphocyte levels to a normal range.

A Quick Review

Lymphocytes are a type of white blood cell that help your immune system fight pathogens. A low lymphocyte count (lymphopenia) can be caused by infections, medications, autoimmune disorders, and blood disorders. A high lymphocyte count (lymphocytosis) can be a sign of infection or some types of cancer.

The treatment for low or high lymphocyte count depends on the underlying cause. However, treatment options may include medication, disease-specific therapies, or supportive care. A nutritious, balanced diet can also support your immune system and help maintain a normal lymphocyte count. 

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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