9.2.1 Types of Immune Cells and Their Roles

Introduction

White blood cells (WBCs) are the main cells of the immune system. They protect the body from infectious diseases and foreign invaders. There are three main types of WBCs: granulocytes, monocytes, and lymphocytes. Each type has specific roles in defending the body. This topic explains the types of immune cells and their functions.

Definition

Immune cells are the cells of the immune system that protect the body from infectious diseases and foreign invaders. White blood cells (WBC) play a significant role in the immune system.

Main Idea

White blood cells (WBC) play a significant role in the immune system by protecting the body from infectious disease and foreign invaders.

WBC are of three main types:

• Granulocytes
• Monocytes
• Lymphocytes

Core Concept

Types of Immune Cells

Detailed Explanation

I) Granulocytes

Granulocytes have granular cytoplasm and nuclei with different shapes. They have three types.

(1) Neutrophils:

- Neutrophils rapidly ingest microorganisms and kill them through phagocytosis.

Simple explanation: Neutrophils are the first responders. They eat and destroy bacteria and other microorganisms.

(2) Basophils:

• Basophils defend the human body from allergens, pathogens, and parasites.
• Basophils release enzymes to improve blood flow and prevent blood clots.

Simple explanation: Basophils defend against allergens and parasites. They release enzymes that improve blood flow.

(3) Eosinophils:

- Eosinophils protect your body from parasites, allergens, foreign bacteria, and outside organisms.

Simple explanation: Eosinophils protect against parasites and allergens.

II) Monocytes

Monocytes are the largest type of white blood cells. Monocytes typically circulate in the blood for 1–3 days before migrating into tissues, where they become macrophages or dendritic cells.

(1) Macrophages:

• Macrophages are specialized cells involved in the detection, phagocytosis, and destruction of bacteria and other harmful organisms.
• In addition, they can also present antigens to T cells and initiate inflammation.

Simple explanation: Macrophages are big eater cells. They detect, eat, and destroy bacteria. They also help T cells recognize invaders and start inflammation.

(2) Dendritic cells:

• These cells instruct T cells on what to attack.
• Also known as antigen-presenting cells.
• Dendritic cells are specialized to take up antigen and display it for recognition by lymphocytes.

Simple explanation: Dendritic cells are like teachers. They show T cells what to attack.

III) Lymphocytes

Lymphocytes help your body's immune system fight cancer and foreign viruses and bacteria (antigens). Lymphocytes help your immune system remember every antigen it comes in contact with.

There are three types of lymphocyte:

• NK cells
• B cells
• T cells

(1) NK cells:

• Natural killer cells (NK cells) are found in blood and lymph.
• They can destroy infected and diseased cells, like cancer cells.
• NK cells develop in bone marrow, lymph nodes, thymus, liver, and uterus.

Simple explanation: NK cells are natural killers. They destroy infected cells and cancer cells.

(2) B cells:

• These lymphocytes arise and mature in the bone marrow.
• When the immune system detects antigens, then B cells produce antibodies to fight the invader pathogen.
• Activated B cells differentiate into plasma cells and memory B cells.

(a) Plasma cells:

- These cells develop from B cells and they make specific type of immunoglobulin (antibodies).

(b) Memory B cells:

• After an encounter, some B cells turn into memory B cells.
• They are long-lived and can produce that specific antibody when the same pathogen attacks in future.

Simple explanation: B cells produce antibodies to fight germs. Plasma cells make antibodies. Memory B cells remember the germ for future attacks.

(3) T cells:

• These lymphocytes arise in the bone marrow and mature in the thymus.
• They gather in lymph nodes.
• T cells upon activation form four types of T cells.

(a) Cytotoxic T cells:

- These are responsible for killing cells infected with viruses.

(b) Helper T cells:

- These specialized lymphocytes help other T cells and B cells to perform their functions.

(c) Memory T cells:

- These cells are formed. They are long-lived and can protect against the same pathogen in future.

(d) Suppressor T cells:

- After infection is controlled, suppressor T cells are formed to shut down the immune response.

Simple explanation: T cells have different jobs:

• Cytotoxic T cells kill infected cells.
• Helper T cells help other immune cells.
• Memory T cells remember the germ for future attacks.
• Suppressor T cells shut down the immune response after the infection is controlled.

Do You Know?

The antigens are markers that indicate a threat like a bacteria or virus has entered your body. Antigens are present on the surface of all cells.

Summary Table

Intermediate Level

White blood cells (WBCs) are the main cells of the immune system.

Key points:

• Granulocytes have granular cytoplasm.
• Monocytes are the largest WBCs.
• Lymphocytes help fight cancer and infections.
• B cells produce antibodies.
• T cells have four types: cytotoxic, helper, memory, suppressor.
• Memory cells provide long-lasting immunity.

Important Points

• - White blood cells (WBC) play a significant role in the immune system by protecting the body from infectious disease and foreign invaders.
• - WBC are of three main types i.e., granulocytes, monocytes and lymphocytes.
• - Granulocytes: Granulocytes have granular cytoplasm and nuclei with different shapes. It has three types:
• - Neutrophils: Neutrophils rapidly ingests microorganisms and kills them through phagocytosis.
• - Basophils: Basophils defend human body from allergens, pathogens and parasites. Basophils release enzymes to improve blood flow and prevent blood clots.
• - Eosinophils: Eosinophils protect your body from parasites, allergens, foreign bacteria and outside organisms.
• - Monocytes: Monocytes are the largest type of white blood cells. Monocytes typically circulate in the blood for 1-3 days before migrating into tissues, where they become macrophages or dendritic cells.
• - Macrophages: Macrophages are specialised cells involved in the detection, phagocytosis and destruction of bacteria and other harmful organisms. In addition, they can also present antigens to T cells and initiate inflammation.
• - Dendritic cells: These cells instruct T cells on what to attack, also known as antigen-presenting cells. Dendritic cells are specialized to take up antigen and display it for recognition by lymphocytes.
• - Lymphocytes: Lymphocytes help your body's immune system fight cancer and foreign viruses and bacteria (antigens). Lymphocytes help your immune system remember every antigen it comes in contact with. There are three types of lymphocyte, NK cells, B-cells and T-cells.
• - NK cells: Natural killer cells (NK cells) are found in blood and lymph. They can destroy infected and diseased cells, like cancer cells. NK cells develop in bone marrow, lymph nodes, thymus, liver, and uterus.
• - B cells: These lymphocytes arise and mature in the bone marrow. When immune system detects antigens, then B cells produce antibodies to fight the invader pathogen. Activated B cells differentiate into plasma cells and memory B cells.
• - Plasma cells: These cells develop from B cells and they make specific type of immunoglobulin (antibodies).
• - Memory B cells: After an encounter, some B cells turn into memory B cells. They are long-lived and can produce that specific antibody when the same pathogen attacks in future.
• - T cells: These lymphocytes arise in the bone marrow and mature in the thymus. They gather in lymph nodes. T cells upon activation form four types of T cells.
• - Cytotoxic T cells: These are responsible for killing cells infected with viruses.
• - Helper T cells: These specialized lymphocytes help other T cells and B cells to perform their functions.
• - Memory T cells: These cells are formed. They are long-lived and can protect against the same pathogen in future.
• - Suppressor T cells: After infection is controlled suppressor T cells are formed to shut down the immune response.
• - The antigens are markers that indicate a threat like a bacteria or virus has entered your body? Antigens are present on the surface of all cells.

Remember

• - WBC = main cells of immune system
• - Three types = granulocytes, monocytes, lymphocytes
• - Granulocytes = neutrophils, basophils, eosinophils
• - Neutrophils = phagocytosis
• - Basophils = allergens, parasites; release enzymes
• - Eosinophils = parasites, allergens
• - Monocytes = macrophages, dendritic cells
• - Macrophages = phagocytosis, antigen presentation, inflammation
• - Dendritic cells = antigen-presenting cells
• - Lymphocytes = NK cells, B cells, T cells
• - NK cells = destroy infected and cancer cells
• - B cells = produce antibodies; plasma cells, memory B cells
• - T cells = cytotoxic, helper, memory, suppressor
• - Memory cells = long-lasting immunity

Common Mistakes

• 1. Confusing granulocytes and lymphocytes.
• - Granulocytes = neutrophils, basophils, eosinophils.
• - Lymphocytes = NK cells, B cells, T cells.
• 2. Mixing up the functions of WBC subtypes.
• - Neutrophils = phagocytosis.
• - Basophils = allergens, parasites.
• - Eosinophils = parasites, allergens.
• 3. Forgetting the role of dendritic cells.
• - Dendritic cells are antigen-presenting cells that instruct T cells.
• 4. Confusing B cells and T cells.
• - B cells = produce antibodies.
• - T cells = cytotoxic, helper, memory, suppressor.
• 5. Thinking NK cells are specific.
• - NK cells are non-specific; they destroy infected and cancerous cells.
• 6. Believing memory cells are short-lived.
• - Memory B and T cells are long-lived.
• 7. Confusing plasma cells and memory B cells.
• - Plasma cells = produce antibodies.
• - Memory B cells = remember the pathogen for future exposure.

Quick Revision

60-Second Revision

• WBC = main cells of immune system
• Three types = granulocytes, monocytes, lymphocytes
• Granulocytes = neutrophils (phagocytosis), basophils (allergens, parasites), eosinophils (parasites, allergens)
• Monocytes = macrophages (phagocytosis, antigen presentation), dendritic cells (antigen-presenting cells)
• Lymphocytes = NK cells (destroy infected and cancer cells), B cells (produce antibodies; plasma cells, memory B cells), T cells (cytotoxic, helper, memory, suppressor)
• Memory cells = long-lasting immunity
• Warning: Do not confuse B cells (produce antibodies) with T cells (cytotoxic, helper, memory, suppressor). Dendritic cells are antigen-presenting cells.