Lymphocytes - Diagram, Count, Types, Roles and Functions

Lymphocytes: Lymphocytes, a type of white blood cell, play a crucial role in the immune system and are present in lymph tissue, blood, and bone marrow. Lymphocytes are immune cells originating in the bone marrow and in blood and lymph tissue. The main types are B lymphocytes, which produce antibodies, and T lymphocytes, which help eliminate tumor cells and regulate immune responses.

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Lymphocytes Diagram

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What are Lymphocytes?

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Lymphocytes Percentage

• Neutrophils: 40% to 60%
• Lymphocytes: 20% to 40%
• Monocytes: 2% to 8%
• Eosinophils: 1% to 4%
• Basophils: 0.5% to 1%

Polygenic Inheritance

Lymphocytes Types

B Lymphocytes

T Lymphocytes

1. T helper (CD4) cells: These cells recognize antigens with class II MHC and trigger various immune cells (like macrophages, B cells, and cytotoxic T cells) to act against antigens by secreting different types of cytokines, which direct the immune response by other cell types.
2. T cytotoxic (CD8) cells: These cells recognize antigens with class I MHC. After activation, they proliferate and differentiate into cytotoxic T lymphocytes, which eliminate virus-infected cells, tumor cells, foreign grafts, etc.

Natural killer (NK) Cells

Lymphocytes Function

1. Recognition of Antigens: Lymphocytes are equipped with receptors that allow them to recognize specific antigens, which are molecules found on the surface of pathogens or foreign substances.
2. Activation of Immune Response: When lymphocytes encounter antigens, they become activated and start to proliferate, or multiply, to mount an immune response.

4. Antibody Production (B cells): B cells are responsible for producing antibodies, which are proteins that bind to antigens and mark them for destruction by other immune cells.
5. Cell-Mediated Immunity (T cells): T cells play a key role in cell-mediated immunity, directly attacking and destroying infected or abnormal cells.
6. Regulation of Immune Response: Lymphocytes help regulate the immune response by producing cytokines, which are signalling molecules that modulate the activity of other immune cells.

6. Memory Response: After an initial encounter with an antigen, some lymphocytes become memory cells. These cells "remember" the antigen and can mount a faster and more effective response upon subsequent exposure.

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Lymphocyte Roles in the Immune System

3. Primary Immune Response: Lymphocytes are crucial for initiating the primary immune response against pathogens. B cells produce antibodies, while T cells help in the destruction of infected cells.
4. Secondary Immune Response: Memory B and T cells play a critical role in the secondary immune response, which is faster and more robust than the primary response due to the presence of memory cells.
5. Immune Surveillance: Lymphocytes constantly patrol the body, scanning for abnormal cells, such as cancer cells, and pathogens.
6. Autoimmunity: In some cases, lymphocytes may mistakenly identify healthy cells as foreign and mount an immune response against them, leading to autoimmune diseases.

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Lymphocytes Normal Range

T Cell Counts

• Above Normal Range: Higher-than-normal T cell counts can indicate conditions such as sexually transmitted infections (STIs) like syphilis, viral infections such as infectious mononucleosis, parasitic infections like toxoplasmosis, tuberculosis, T-cell acute lymphoblastic leukemia, or multiple myeloma.
• Below Normal Range: Lower-than-normal T cell counts can indicate a congenital disease, an acquired T cell deficiency like HIV, or a type of cancer like DiGeorge syndrome.

B Cell Counts

• Above Normal Range: Elevated B cell counts may suggest conditions such as chronic lymphocytic leukemia (CLL), multiple myeloma, or Waldenström macroglobulinemia.
• Below Normal Range: Reduced B cell counts may suggest conditions like B-cell acute lymphoblastic leukemia, HIV, or another immune system-weakening disease like DiGeorge syndrome.

Lymphocytes High Levels (Lymphocytosis)

1. Hepatitis: Inflammation of the liver caused by a viral infection or other factors.
2. Syphilis: A sexually transmitted infection caused by the bacterium Treponema pallidum.
3. Mononucleosis: Commonly known as "mono," a viral infection caused by the Epstein-Barr virus.
4. Tuberculosis: An infectious disease caused by the bacterium Mycobacterium tuberculosis that primarily affects the lungs.
5. HIV and AIDS: Infection with the human immunodeficiency virus (HIV) can lead to acquired immunodeficiency syndrome (AIDS), a condition in which the immune system is severely compromised.
6. Underactive Thyroid (Hypothyroidism): A condition where the thyroid gland does not produce enough thyroid hormone.
7. Infections: Other infections, such as whooping cough, toxoplasmosis, or cytomegalovirus.
8. Blood Cancers: Conditions such as lymphoma or leukemia, which involve abnormal production of white blood cells.

Lymphocytes Low Level (Lymphocytopenia)

1. HIV or AIDS: The human immunodeficiency virus (HIV) can lead to a decrease in lymphocyte levels.
2. Tuberculosis or Typhoid Fever: Infections such as tuberculosis or typhoid fever can result in lymphocytopenia.
3. Viral Hepatitis: Inflammation of the liver caused by a viral infection.
4. Blood Diseases: Conditions such as Hodgkin's disease, a type of lymphoma, can lead to a decrease in lymphocytes.
5. Autoimmune Diseases: Disorders like lupus, where the immune system attacks healthy tissues, can cause lymphocytopenia.
6. Rare Inherited Conditions: Genetic disorders such as severe combined immunodeficiency (SCID), ataxia-telangiectasia, DiGeorge syndrome, and Wiskott-Aldrich syndrome can result in low lymphocyte levels.
7. Radiation or Chemotherapy Treatments: Therapies used to treat cancer can suppress the immune system and reduce lymphocyte levels.