Things To Know About Lymphocytes

What are Lymphocytes?

Lymphocytes are one of the three main types of white blood cells (granulocytes, monocytes, and lymphocytes). They are a part of the body’s adaptive immunity and play a crucial role in fighting against infection and disease-causing microbes. Lymphocytes are high in number in blood and lymph (the colorless fluid that connects lymph nodes to blood circulation). The lymphatic system is a network of small and large vessels, organs, and tissues that protect the body.

Lymphocytes develop in primary lymphoid organs (the thymus gland and hematopoietic or blood-forming tissue in the bone marrow) and most of them die without functioning at all. The rest of the cells are constantly circulating between the lymph and blood. When they encounter or recognize a foreign antigen in a peripheral lymphoid organ (lymph nodes, spleen), lymphocytes proliferate into different types of cells to attack the foreign cells.

An antigen is a marker, usually a protein found on the surface of cells. If they are foreign to the body, they are tagged and identified by lymphocytes. Lymphocytes then migrate through the blood to the site of infection. Lymphocytes are the highest in number in lymph nodes. These nodes are small organs that filter lymph and isolate microbes that can be later attacked by lymphocytes. Lymphocytes differentiate into different types only when they are activated by a foreign cell.

Functions of Lymphocytes

The main function of lymphocytes is to fight foreign cells like viruses, bacteria, and cancer by identifying the antigens on these cells. They are an important component of the body's immune system to fight infection.

An important property of lymphocytes that helps them perform this function is their memory. Every time they encounter an antigen, they store it in memory. The next time they encounter the same antigen, they can recognize it and respond quickly. This is the basis of how vaccinations work to prevent certain infections.

Types of Lymphocytes

Lymphocytes are of three main types, with each having its subtypes.

1. B Cells or B Lymphocytes

B cells are responsible for humoral or antibody-mediated immunity. An antibody is a protein that binds to a specific antigen. There are 2 categories of B lymphocytes:

• Plasma cells: Produce antibodies in response to an infection. The antibodies or immunoglobulins bind to the antigens to neutralize them or prepare them for destruction by other cells.
• Memory B cells: Help to remember and recognize foreign cells and attack them if the infection returns.

 

1. T Cells or T Lymphocytes

T cells are involved in cell-mediated immunity in which there is the activation of cells and release of chemicals like cytokines in response to an antigen. The different types of T lymphocytes are:

• Cytotoxic cells: Upon being activated, they kill infected cells.
• Helper cells: Are involved in gathering other cells to fight the infection.
• Natural killer (NK) cells: Are capable of killing certain cancer cells and other infection-causing cells. They are part of the innate (frontline) immune response, distinct from adaptive T cells.
• Regulatory T cells: Help to regulate the entire reaction and prevent any harm to the body that can be caused by overreaction (as in autoimmune conditions).
• Memory T cells: Are responsible for remembering antigens to launch attacks if reinfection happens.

Where Are Lymphocytes Found?

B and T lymphocytes develop from stem cells present in the bone marrow. Some immature cells migrate from the bone marrow to the thymus gland where they become T cells. B cells develop within the bone marrow.

Both B and T cells migrate to peripheral lymphoid organs like the spleen and lymph nodes from where they react with antigens.

How Do Lymphocytes Look?

Lymphocytes are microscopic, larger than red blood cells but fewer in number. They consist almost entirely of a large central nucleus surrounded by a jelly-like cytoplasm. When observed after staining, the nucleus is dark purple, and the cytoplasm becomes lighter pink.

Lymphocytes Normal Range

Usually, lymphocytes constitute about 20–40% of the total white blood cells in the blood. The normal lymphocyte count depends on various factors like age, sex, altitude, and lifestyle.

In adults, the absolute count ranges from 1,000 to 4,800 per microliter of blood. In children, it ranges from 3,000 to 9,500 lymphocytes per microliter.

What Does a High Lymphocyte Count Mean?

When the count of lymphocytes is high (>4,000/μL in adults), it is called lymphocytosis. It usually means the body is producing more lymphocytes to fight an infection or illness such as:

• Recent viral infection
• Chronic medical conditions like rheumatoid arthritis
• An allergic reaction to a medicinal drug
• Trauma
• Splenectomy (surgical removal of the spleen)

Lymphocytosis can also indicate certain serious conditions, such as: hepatitis, syphilis, primary HIV or AIDS, whooping cough, tuberculosis, toxoplasmosis, cytomegalovirus, or blood cancers like leukemia and lymphoma. High lymphocytes may be an early indicator but require further diagnostic evaluation. High lymphocyte count cannot usually be prevented, but it can be managed by treating the underlying cause.

How Does a Low Lymphocyte Count Affect Health?

Lymphocytopenia or lymphopenia is the opposite of high lymphocyte count and refers to a condition in which the lymphocyte count in blood is lower than normal (<1,000/μL in adults or <3,000/μL in children under 2 years). Poor nutrition, corticosteroids, or infections are common risk factors. The condition makes a person prone to infection. It could be caused by mild infections like the flu or due to more serious conditions like: HIV or AIDS, tuberculosis, typhoid, viral hepatitis, Hodgkin’s lymphoma, autoimmune conditions like systemic lupus erythematosus, radiation therapy, chemotherapy, or rare inherited conditions such as SCID (Severe Combined Immunodeficiency) syndrome.

Common Tests to Check The Health of Lymphocytes

The following are some of the tests to check lymphocyte count in a blood sample:

• Absolute Lymphocyte Count (ALC): As part of a complete blood count (CBC). A CBC gives the percentage of each type of white blood cell. Multiplying the total white blood cell count by the lymphocyte percentage gives the ALC.
• Flow Cytometry: This advanced test processes blood in a special laboratory. The blood sample is suspended in a fluid and passed through a laser-generating instrument. The laser scatters blood cells into patterns to count and analyze individual cells.

Symptoms of Lymphocyte Count Imbalance

Lymphocytosis Symptoms
A blood disorder or any cancer may lead to a high lymphocyte count with a few symptoms like:

• Enlarged lymph nodes
• Fever, night sweats
• Pain in the abdomen
• Loss of appetite
• Shortness of breath

Lymphopenia Symptoms
Lymphopenia may not cause any symptoms, but when found during testing, signs may include:

• Recurrent infections like the common cold
• Fungal or parasitic infections
• Chronic infections like tuberculosis
• Enlarged or swollen lymph nodes
• Smaller or missing tonsils
• Sudden hair loss, chronic itch, red skin
• Small swellings on the skin that turn into open sores
• Jaundice
• Ulcers in the mouth
• Enlarged spleen.

Conclusion

Lymphocytes play a vital role in immunity by combating infections and diseases. Understanding their functions, normal ranges, and symptoms of imbalances helps identify potential health issues early. Proper diagnostic tests and timely treatment can manage conditions like lymphocytosis and lymphopenia effectively.

Frequently Asked Questions 

1. What are Lymphocytes?

Lymphocytes are white blood cells that play a crucial role in the immune system, helping the body fight infections and diseases. 

2. What is The Normal Range of Lymphocytes?

In adults, the normal range is 1,000 to 4,800 lymphocytes per microliter of blood.

3. What Causes High Lymphocyte Counts?

High lymphocyte counts, or lymphocytosis, can result from viral infections, chronic diseases, or blood cancers like leukemia.

4. How Does Low Lymphocyte Count Affect Health?

Low lymphocyte count, or lymphopenia, can weaken the immune system, increasing the risk of infections.

5. Where are Lymphocytes Found in The Body?

Lymphocytes are primarily found in the blood, lymph nodes, spleen, and other lymphoid organs.

Disclaimer

This article provides general educational information about lymphocytes and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for personalized evaluation, especially if you have abnormal blood test results or symptoms. Self-diagnosis or treatment based on this content is not recommended.

References

1. Abbas, A. K., Lichtman, A. H., & Pillai, S. (2020). Basic immunology: Functions and disorders of the immune system (6th ed.). Elsevier.
https://www.elsevier.com/books/basic-immunology/abbas/978-0-323-54943-1

2. Janeway, C. A., Travers, P., Walport, M., & Shlomchik, M. J. (2001). Immunobiology: The immune system in health and disease (5th ed.). Garland Science. 

https://www.ncbi.nlm.nih.gov/books/NBK27092/

3. Centers for Disease Control and Prevention. (2023). Immune system and vaccines. 

https://www.cdc.gov/vaccines/basics/immunity-types.html

4. National Cancer Institute. (2024). Lymphocytopenia. 

https://www.cancer.gov/publications/dictionaries/cancer-terms/def/lymphocytopenia

5. American Society of Hematology. (2023). Flow cytometry. 

https://www.hematology.org/education/patients/blood-basics/flow-cytometry