Lymphocytes are a type of white blood cell. These cells are created by your bone marrow. B cell lymphocytes stay in your bone marrow, while T cell lymphocytes travel to your thymus.
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, it means there aren’t enough white blood cells in your bloodstream.
Your bone marrow constantly
Some new lymphocytes remain in the bone marrow and become B cells. The others 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.
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
- helper T cells
- regulatory T cells
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 substances that cause an allergic reaction, such as pollen, molds, or pet dander.
If you show symptoms of an infection and a suspected blood disorder, 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.
A few factors can affect the results of your blood test. Tell your doctor if you have or have had:
- a recent infection
- chemotherapy
- radiation therapy
- steroid therapy
- HIV
- surgery
- pregnant
- high stress
Laboratories often have different ways of measuring blood test results. Results also vary by:
- age
- gender
- heritage
- how high above sea level you live
The following table gives approximate ranges for adults, but you’ll want to talk with your doctor about your results. Some factors may determine your normal range.
| Test | Adult normal cell count | Adult normal range (differential) | Low levels | High levels |
| white blood cells (WBC) | 4,500 to 10,000 (4.5 to 10.0) white blood cells/mcL | 1% of total blood volume | critical when fewer than 2,500 lymphocytes/mcL | critical when greater than 30,000/mcL |
| lymphocytes | 800 to 5000 (0.8 to 5.0) lymphocytes/mcL | 18 to 45% of total white blood cells | fewer than 800 lymphocytes/mcL | greater than 5,000 lymphocytes/mcL |
A low lymphocyte count, called
- Your body isn’t producing enough lymphocytes.
- Lymphocytes are being destroyed.
- Lymphocytes are trapped in your spleen or lymph nodes.
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:
- undernutrition
- HIV and stage 3 HIV
- influenza
- autoimmune conditions, such as lupus
- some cancers, including lymphocytic anemia, lymphoma, and Hodgkin’s disease
- steroid use
- radiation therapy
- certain drugs, including chemotherapy drugs
- some inherited disorders, such as Wiskott-Aldrich syndrome and DiGeorge syndrome
- viral infections, including measles, mumps, and mononucleosis
- adenovirus
- hepatitis
- influenza
- tuberculosis
- toxoplasmosis
- cytomegalovirus
- brucellosis
- vasculitis
- acute lymphocytic leukemia
- chronic lymphocytic leukemia
- HIV and stage 3 HIV
You may find it helpful to ask the following questions if your doctor orders a B and T cell screen:
- Why do you think I need this test?
- Are you testing for a specific condition?
- Do I need to do anything special to prepare for the test?
- How soon will I get the results?
- Who will give me the results and explain them to me?
- If the test results are normal, what will the next steps be?
- If the test results are abnormal, what will the next steps be?
- What self-care steps should I be taking while waiting for the results?
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.