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Immunity and infection prevention

B, T and NK lymphocytes

Lymphocytes are the “specialists” of the immune system. There are three main families: B cells, which make antibodies; T cells, which direct the defence and destroy infected cells; and natural killer (NK) cells, which react quickly. This topic explains what each family does and why it matters for understanding leukemia and its treatment.

Last updated: ~5 min read
Three groups of glowing round cells on a dark navy background: lymphocytes picked out in turquoise, gold and reddish light.
Figure 1.Concept: B, T and NK lymphocytes are the three main “specialist” families of the immune system.

01Short answer

Lymphocytes are white blood cells made in the bone marrow and found in the blood, lymph nodes, spleen and other lymphoid tissue. B cells mature in the bone marrow; when activated, they turn into plasma cells and make antibodies. T cells mature in the thymus: helper T cells switch on other immune cells, while cytotoxic T cells destroy virus-infected and tumour cells. NK cells are part of innate immunity and recognise changed cells without prior “training”. Some B and T cells become memory cells. Leukemia can also start in lymphocytes: most CLL arises from B cells, and ALL from early forms of B or T cells. Some modern treatments, such as monoclonal antibodies, T-cell engagers and CAR-T, are based on the properties of lymphocytes.

02Simple explanation

There are several kinds of white blood cells. Lymphocytes are one of them and are seen as the “smartest” immune cells: each one can recognise one particular germ.

B cells are “antibody factories”. A B cell that recognises its germ multiplies and turns into a plasma cell. Plasma cells release large amounts of antibodies into the blood; the antibodies stick to the germ and make it harmless.

T cells do two main jobs. Helper T cells are like “commanders”: they send signals to other cells. Cytotoxic (killer) T cells find and destroy cells that are infected with a virus or have become cancerous.

NK cells (natural killers) are “sentries”. They quickly recognise cells with a changed surface, such as virus-infected or tumour cells, and destroy them without needing to have met that germ before.

The link with leukemia: when early forms of lymphocytes multiply out of control, ALL develops; when mature B lymphocytes build up, the result is most often CLL. Some medicines also lower healthy lymphocytes, which is why a doctor may prescribe extra prevention.

03Scientific explanation

Origin and maturation: according to the NCI and InformedHealth, lymphocytes come from stem cells in the bone marrow. B cells mature in the bone marrow and T cells in the thymus (hence the letters in their names). According to MedlinePlus, lymphocytes usually make up 20–40% of all white blood cells.

Recognition: according to InformedHealth and Chaplin, every B and T cell carries a receptor on its surface that recognises only one kind of antigen, like a lock and key. When a matching germ turns up, only that cell multiplies, which is why the adaptive immune response is precise but takes several days the first time.

Types of T cells: according to the NCI dictionary, helper T cells (CD4-positive) stimulate killer T cells, macrophages and B cells; cytotoxic T cells kill foreign, cancer and virus-infected cells; and regulatory T cells keep the immune system from becoming overactive.

NK cells: according to the NCI, NK cells have granules containing enzymes that kill tumour cells and virus-infected cells. According to a review by Vivier and colleagues, although NK cells are classed as part of innate immunity, they can show some features of adaptive immunity, including memory-like responses.

04What happens in the body?

Where do lymphocytes live?

Lymphocytes circulate in the blood, but most of them live in the lymph nodes, spleen, tonsils and the lymphoid tissue of the gut wall. They constantly move between the blood and the lymph, searching for “their” germ. When they find it, they multiply in a lymph node, and the node may swell.

B cells and antibodies

According to InformedHealth, helper T cells send signals to matching B cells; these B cells multiply and turn into plasma cells. Plasma cells produce large amounts of antibodies in a short time. Some activated B cells become memory cells and speed up the response the next time the same germ appears.

Many small Y-shaped particles of light spreading out from a large glowing cell on a dark navy background.
Figure 2.A B cell that has become a plasma cell releases many antibodies.

How do killer cells work?

Cytotoxic T cells and NK cells matter against threats hidden inside cells. Because a virus multiplies inside a cell, antibodies cannot reach it there. Killer cells recognise the infected cell by changes on its surface and destroy it, which stops the virus from spreading.

The moment a small glowing immune cell touches a larger cell with a changed surface on a dark navy background, with gold light at the point of contact.
Figure 3.A killer cell recognises a virus-infected cell.

Lymphocytes and leukemia

According to the American Cancer Society, the common form of CLL starts in B lymphocytes. ALL can arise from early forms of B or T cells; T-cell ALL is less common than B-cell ALL. Immunophenotyping (flow cytometry) shows which lymphocyte family a leukemia cell belongs to, and this matters for choosing treatment.

How does treatment affect lymphocytes?

Some treatments use lymphocytes: CAR-T is made from the patient’s own T cells, and blinatumomab brings T cells close to leukemia cells. Other treatments, such as long courses of steroids, can lower healthy lymphocytes; in that case your team may prescribe prevention against certain infections.

05How do lymphocytes fight a germ?

A simplified sequence.

Recognition — A lymphocyte with a matching receptor recognises the germ’s antigen.1RecognitionA lymphocyte with a matching receptor recognises the germ’s antigen.
Activation — Helper T cells send signals.2ActivationHelper T cells send signals.
Multiplying — Matching B and T cells multiply quickly.3MultiplyingMatching B and T cells multiply quickly.
Attack and memory — Antibodies and killer cells act, and memory remains.4Attack and memoryAntibodies and killer cells act, and memory remains.
B cellsMake antibodies.
T cellsDirect and kill.
NK cellsQuickly find changed cells.

06The three lymphocyte families at a glance

FeatureB cellsT cellsNK cells
Where they matureBone marrowThymusMainly bone marrow
Main jobMake antibodies (as plasma cells)Direct other cells, kill infected cellsQuickly kill infected and tumour cells
Type of immunityAdaptiveAdaptiveInnate
MemoryYesYesSome memory-like features
Link with leukemiaCLL, B-cell ALL, hairy cell leukemiaT-cell ALLRare NK-cell leukemias

* This table is simplified. Research on where NK cells mature is ongoing.

07Key terms

Lymphocyte
An immune cell made in the bone marrow and found in the blood and lymphoid tissue.
B cell
A lymphocyte that makes antibodies once activated.
Plasma cell
A cell derived from an activated B cell that produces large amounts of antibody.
T cell
A lymphocyte that matures in the thymus and directs the immune response or kills cells.
Helper T cell
A CD4-positive T cell that stimulates other immune cells.
Cytotoxic T cell
A T cell that kills infected and cancer cells.
Regulatory T cell
A T cell that keeps the immune system from becoming overactive.
NK cell
An innate immune cell that quickly kills infected and tumour cells.
Lymphopenia
A lower-than-normal number of lymphocytes in the blood.
Immunophenotyping
A lab method that identifies cells by the markers on their surface.

08Key points

  • Lymphocytes are made in the bone marrow and are a type of white blood cell.
  • B cells turn into plasma cells and make antibodies.
  • T cells direct the immune response and destroy infected cells.
  • NK cells recognise changed cells without prior “training”.
  • Some B and T cells become memory cells.
  • CLL mostly arises from B cells; ALL from early forms of B or T cells.
  • CAR-T and some antibody medicines are based on the properties of lymphocytes.
  • Your team decides on prevention during treatments that lower lymphocytes.

09Frequently asked questions

My lymphocytes are high. Does that mean leukemia?

Not necessarily. Lymphocytes also rise during viral infections. If the rise is lasting and unexplained, a doctor may order further tests, such as flow cytometry.

My lymphocytes are low. Is that dangerous?

Low lymphocytes (lymphopenia) can make some infections more likely, especially if it lasts a long time. Your team decides on the cause and what to do based on your situation.

In CLL I have lots of lymphocytes, so why do I get ill so often?

In CLL, the multiplying B cells do not work properly, and the production of healthy antibodies can fall. So even with a high lymphocyte count, your defences can be weaker.

What is CAR-T?

According to the NCI, CAR-T is made from the patient’s own T cells: the cells are changed in the lab so that they recognise and destroy leukemia cells. We cover it in more detail in the immunotherapy topic.

Do NK cells fight leukemia?

NK cells can recognise and kill tumour cells, and this ability is being studied for use in treatment. But on their own they cannot stop leukemia from developing.

How can I strengthen my lymphocytes?

There are no proven foods or supplements that specifically “boost” lymphocytes. Sleep, a balanced diet, movement and protection from infections support your general health. Check any supplement with your team.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. What is my lymphocyte count, and what does it mean?

  2. How does treatment affect my B or T cells?

  3. Should my immunoglobulin levels be checked?

  4. When will my lymphocytes recover?

My questions

12Sources

  1. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: lymphocyte
  2. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: B cell
  3. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: T cell
  4. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: helper T cell
  5. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: natural killer cell
  6. InformedHealth.org (IQWiG). The innate and adaptive immune systems
  7. Journal of Allergy and Clinical Immunology, 2010. Chaplin DD. Overview of the immune response
  8. Science, 2011. Vivier E et al. Innate or adaptive immunity? The example of natural killer cells
  9. MedlinePlus (U.S. National Library of Medicine). Blood differential test
  10. American Cancer Society. What Is Chronic Lymphocytic Leukemia?
  11. American Cancer Society. Acute Lymphocytic Leukemia Subtypes and Prognostic Factors
  12. American Cancer Society. Immunotherapy for Acute Lymphocytic Leukemia
  13. National Cancer Institute (NCI). CAR T Cells: Engineering Patients’ Immune Cells to Treat Their Cancers
  14. Blood, 2018. iwCLL guidelines for diagnosis, indications for treatment, response assessment, and supportive management of CLL
  15. Journal of Clinical Oncology (ASCO and IDSA), 2018. Antimicrobial Prophylaxis for Adult Patients With Cancer-Related Immunosuppression: ASCO and IDSA Clinical Practice Guideline Update
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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