What Are Lymphocytes?

Medically Reviewed by Zilpah Sheikh, MD on September 20, 2023
Written by WebMD Editorial Contributor
6 min read

Lymphocytes are a type of white blood cell.

The color of your blood comes from your red blood cells. These carry oxygen through your body. You have fewer white blood cells than red blood cells. But they play an important role. They defend your body from infection.

Lymphocytes are an important part of your immune system. About 20%-40% of your white blood cells are lymphocytes.

Your lymphocytes act like your body's army. They help your body's immune system fight cancer, viruses, and bacteria (antigens). They're dispersed throughout your body, but once an organism or virus invades, they immediately gather to fight it off. They're responsible for your antibody production, they direct the destruction of your virus-infected and tumor cells, and they regulate your immune response.

Additionally, your lymphocytes can turn into a kind of memory cell that helps your immune system remember every antigen it comes in contact with. When your memory cells run into the same antigen again, they respond right away. This explains why you don't get some infections (like measles or chicken pox) more than one time. This is why vaccines can prevent certain disorders.

Lymphocytes are formed in your bone marrow. As they mature, they go into your bloodstream. Mature lymphocytes are found in your blood and all parts of your lymphatic system. That's group of organs, vessels, and tissues that keep you safe from infections. They also help you maintain a healthy balance of fluids. Your lymphatic system includes your bone marrow, thymus gland, and lymph nodes.

Types of lymphocytes

There are two main types of lymphocytes:

  • B cells (B lymphocytes). These make antibodies. Antibodies can destroy foreign substances or tag them for attack.
  • T cells (T lymphocytes). These lymphocytes destroy any of your cells that have been taken over by viruses or cancers.

Your B cells and T cells work together, and each have important roles in your immune system.

B cells

These types of lymphocytes have receptors on their surfaces where antigens attach. Your B cells learn to recognize antigens. They make antibodies to attack each one. Your B cells respond to antigens in two ways:

  • Primary immune response. This is when an antigen attaches to a receptor and your B cells are stimulated. Some of your B cells change into memory cells. Others turn into plasma cells. Plasma cells make an antibody tailored to the antigen that stimulated it. Making enough of an antibody can take several days.
  • Secondary immune response. This happens when your B cells comes into contact with that antigen again. Your memory cells remember that antigen, and they multiply. They change into plasma cells and produce the antibody you need.

T cells

These help destroy your infected cells and control your body's immune response. But most of your T cells need help from another immune cell to work. Once they're activated, they multiply and specialize into different types of T cells. These include:

  • Cytotoxic (killer) T cells. These attach to antigens on your infected or abnormal cells. They kill those infected cells by making holes in their cell membranes and placing enzymes into those cells.
  • Helper T cells. Like their name implies, these help your other immune cells. Some also help your B cells make antibodies against foreign invaders. Others help activate your cytotoxic T cells.
  • Regulatory (suppressor) T cells. These make substances that help stop your immune system's response. They can prevent harmful responses.

Natural killer cells

These are a type of lymphocyte that kills infected and diseased cells, like cancer cells. They can kill harmful cells in the early stages, which can keep viruses and cancer cells from spreading.

There are a few blood tests that test for white blood cells.

Complete blood count (CBC). A CBC is a blood test that measures different components of your blood. It measures:

  • Red blood cells
  • White blood cells
  • Platelets, the cells which help with blood clotting
  • Hemoglobin, the protein in your blood that carries oxygen
  • Hematocrit, which is the ratio of red blood cells to plasma (the fluid component of your blood)

If your blood is only to be used for the CBC, you don't need to fast and can eat and drink normally. A doctor will take a sample of your blood and send it in to a lab for testing.

Flow cytometry. This is a commonly used test that looks at many types of blood cells. It's more detailed than a CBC and can measure the levels of different lymphocytes.

Your doctor will take a sample of your blood and send it to a lab. A technician will suspend your blood sample in a fluid and send it through an instrument called a flow cytometer.

This instrument contains lasers and detectors. As your blood cells pass through the lasers, they scatter light in certain patterns that are detected by the flow cytometer. This allows the number and types of cells in your sample to be counted. Thousands of cells can be analyzed in a few minutes.

B and T cell screen. This is a kind of lymphocyte blood test done in a lab to find the amount of B and T lymphocytes in your blood. Your doctor might order this test if you have signs of diseases that weaken your immune system. This test can also be used to tell the difference in cancers and noncancers, particularly cancers of the blood and bone marrow.

Your doctor will need a sample of your blood. This can be done by a fingerstick (or a heel stick in infants).

After your blood is drawn, it'll go through a two-step process:

  1. Your lymphocytes will be separated from other blood parts.
  2. Identifiers are then added so your doctor can tell between your T and B cells.

The normal range of lymphocytes varies depending on your age, race, sex, altitude, and lifestyle. It can vary among different labs. Some labs may have different ways of measuring blood test results or they may test different samples. Talk to your doctor about your blood test results and what the numbers mean.

In adults, your normal range of lymphocytes is between 1,000 and 4,800 lymphocytes in every 1 microliter of blood. In children, the normal range of lymphocytes is between 3,000 and 9,500 lymphocytes in every 1 microliter of blood. About 20%-40% of your white blood cells are lymphocytes.

High lymphocytes

Having a high level of lymphocytes is called lymphocytosis. That can happen because of an infection or illness. Your body might make extra lymphocytes to help fight that infection or illness. But you might have a serious condition causing your high lymphocyte count, such as:

  • Hepatitis
  • Syphilis
  • Mononucleosis
  • HIV or AIDS
  • Tuberculosis (TB)
  • Underactive thyroid
  • Whooping cough, toxoplasmosis, cytomegalovirus, or other infections
  • Lymphoma, leukemia, or other blood cancers

Low lymphocytes

Having low levels of lymphocytes in your blood is called lymphopenia. You might get this from the flu or other mild infections, but it might be caused by something more serious, such as:

  • HIV or AIDs
  • TB
  • Typhoid fever
  • Viral hepatitis
  • Hodgkin's disease or other blood diseases
  • Lupus or other autoimmune diseases
  • Severe combined immunodeficiency, ataxia-telangiectasia, DiGeorge syndrome, Wiskott-Aldrich syndrome, or another rare inherited disease
  • Radiation
  • Chemotherapy
  • Lymphocytes are a type of white blood cell.
  • Lymphocytes are an important part of your immune system.
  • Your lymphocytes help your body's immune system fight cancer, viruses, and bacteria (antigens).
  • Your lymphocytes can be a kind of memory cell that helps your immune system remember an antigen—and form a quick attack when it encounters that antigen again.
  • The normal range of lymphocytesvaries depending on your age, race, sex, altitude, and lifestyle.

What does it mean when your lymphocytes are low?

You might have the flu or a mild infection. But you might have something more serious, so see your doctor if you have symptoms.

What are common symptoms of lymphocyte conditions?

You may not have any symptoms. But possible ones include:

What does it mean if your lymphocyte level is high?

It probably means your body is fighting an infection or illness. See your doctor if you have symptoms.

What do lymphocyte test results tell you?

If your lymphocyte count is higher or lower than average, your body may be fighting an infection. Talk to your doctor about your test results. They can help find out what's causing your high or low lymphocyte levels and what you can do to bring it back to normal.