5 Things To Know About Lymphocytes

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Lymphocytes are a type of white blood cell (WBC). There are two varieties: T cells and B cells. Both play a critical role in your immune system by helping your body fight infection and disease.

This article reviews five key facts about lymphocytes, including where they are found, what they look like, how the two kinds differ, how doctors test for them, and what diseases are associated with them.

Blood tube sitting on blood results with technician at microscope in lab
Andrew Brookes / Getty Images

Where They Are Found

Like all blood cells, lymphocytes begin their life’s journey in the bone marrow, which is spongy, soft tissue located in the center of your bones.

Once lymphocytes are formed within your bone marrow, they travel to and perform various functions within your lymphatic system.

Your lymphatic system is an intricate network of lymph channels, nodes, tissues, and organs that work together to release lymphocytes and other infection-fighting cells.

Small, bean-shaped structures called lymph nodes are strategically situated along the network of lymphatic channels. Lymphocytes can travel to your lymph nodes where they monitor for and destroy foreign invaders, such as bacteria, viruses, parasites, fungi, and other toxins.

Besides your lymph nodes, lymphocytes can also gather within various lymphoid tissues and organs in your body, such as your spleen, tonsils, intestines, and the lining of your airways.


Lymphocytes are white blood cells that are found in your bloodstream, lymph nodes, lymph channels, and various tissues and organs like your spleen and gut.

Types of Lymphocytes

There are two main kinds of lymphocytes—T cells and B cells.

T Cells

T cells are involved in cell-mediated immunity—what's essentially cell-to-cell combat.

T cells travel from your bone marrow to your thymus, a small gland located behind your breastbone, where they begin maturing into a specific type of T cell.

The different types of T cells include:

  • Cytotoxic T cells, which find and directly attack "foreigners" such as bacteria, viruses, and cancer cells
  • Helper T cells, which recruit other immune system cells and organize a specialized immune response
  • Regulatory T cells thought to suppress the immune system so that it doesn't overreact, as it does in autoimmune diseases
  • Natural killer T (NKT) cells, which respond to the presence of cancer cells in the body
  • Memory T cells, which remember markers on the surface of foreign invaders that they have seen before

B Cells

Once formed in the bone marrow, B cells travel to the spleen and lymph nodes.

Unlike T cells, B cells don't kill foreign invaders themselves. Rather, they produce Y-shaped proteins called antibodies that attach to the surfaces of invaders and disable them or serve as markers for destruction by other immune system cells. This process is called humoral immunity.

There are two main types of B cells:

  • Plasma cells produce large volumes of antibodies that stick to foreign invaders in your body.
  • Memory B cells help your body remember the foreign invaders should they infect your body again in the future.


There are two main kinds of lymphocytes. While B cells help the body identify things that can do it harm, T cells mainly seek them out and destroy them.

What They Look Like

Lymphocytes are not visible to the naked eye. This means that they can only be seen when a drop of blood is smeared on a slide, treated with the right stains, and placed under a microscope.

When looking under the microscope, lymphocytes will be bigger and fewer in number compared to red blood cells, which carry oxygen and give blood its color.

Also, lymphocytes are almost entirely composed of a nucleus, which is a DNA-storing structure located in the middle of the cell. With the proper stain, the nucleus of a lymphocyte is dark purple, while the surrounding jelly-like fluid—what's known as cytoplasm—is lighter pink.


Your doctor may order lymphocyte testing if they suspect or are monitoring the progression of certain health conditions.

A simple blood test called a complete blood found (CBC) with differential can reveal the percentage level of lymphocytes and other white blood cells in your bloodstream.

A more advanced test called flow cytometry can identify and count all different kinds of cells in your blood, including lymphocytes.

With flow cytometry, your blood is drawn from a vein and sent off to a special laboratory where it is suspended in a fluid and passed through a special laser-producing instrument. The light produced from the laser scatters the cells in such a way that they can be individually analyzed.

A normal lymphocyte count depends on your age. For young and middle-aged adults in good health, it is generally between 780 and 3500 lymphocytes per microliter of blood.

Associated Diseases

Having too many lymphocytes in your blood is called lymphocytosis, while having too few is called lymphopenia.

Either may inform a new diagnosis, indicate worsening of an existing one, or indicate consequences of certain medical treatments.

Possible causes of lymphocytosis include:

Possible causes of lymphopenia include:

Call Your Doctor

It's important to reach out to your doctor if you are experiencing persistent, recurring, or severe symptoms of infection or a whole-body illness. Some of these symptoms may include fever, weight loss, unusual fatigue, swollen lymph nodes, and night sweats.


Lymphocytes are white blood cells that work hard to fight off infection and disease in your body. They are made in your bone marrow and move throughout your lymphatic system.

A normal lymphocyte count depends on your age. Having too many or too few may be a sign of a mild or serious illness.

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11 Sources
Verywell Health 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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