9.2.1 Killing Cells of Blood

There are white blood cells in the body called phagocytes. A phagocyte is a cell that destroys other abnormal body cells (cancerous cells) or invaded microorganisms by engulfing. This process is called phagocytosis. Main types of phagocytic white blood cells are macrophages, dendritic cells, and neutrophils.

Definition

Phagocyte: A phagocyte is a cell that destroys other abnormal body cells (cancerous cells) or invaded microorganisms by engulfing. This process is called phagocytosis.

Phagocytosis: Phagocytosis is the process by which a phagocyte engulfs and destroys abnormal body cells or invaded microorganisms.

Main Idea

• There are white blood cells in the body called phagocytes.
• A phagocyte destroys abnormal body cells or invaded microorganisms by engulfing.
• This process is called phagocytosis.
• Main types of phagocytic white blood cells are:

Core Concept

• Phagocytes = white blood cells that engulf and destroy
• Phagocytosis = process of engulfing and destroying
• Main types = macrophages, dendritic cells, neutrophils
• Monocytes = formed in bone marrow; become macrophages or dendritic cells
• Macrophages = found in organs; engulf and destroy microbes
• Dendritic cells = found in tissues; antigen-presenting cells
• Neutrophils = granulocytes; short-lived; highly mobile; release lysosomal enzymes

Detailed Explanation

Killing Cells of Blood

• There are white blood cells in the body called phagocytes.
• A phagocyte is a cell that destroys other abnormal body cells (cancerous cells) or invaded microorganisms by engulfing.
• This process is called phagocytosis.
• Main types of phagocytic white blood cells are: macrophages, dendritic cells, and neutrophils.

Macrophages and Dendritic Cells

• Monocytes are formed in bone marrow.
• From bone marrow, monocytes typically circulate in the blood for 1-3 days before migrating into tissues, where they become macrophages or dendritic cells.
• Through blood, macrophages and dendritic cells are transported to the areas of the body where they are needed.
• Macrophages are generally found in the organs such as the lungs, liver, spleen, kidney and lymph nodes, rather than remaining in the blood.
• In these organs, they patrol within the free spaces among the cells and provide protection by trapping and destroying microorganisms entering the tissue.
• As macrophages interact with microbes, they not only engulf and destroy them; they also display some parts of microbes on their surface so that other body cells may also be informed.
• Such cells are called Antigen Presenting Cells (APCs).
• The macrophages also secrete many different proteins when they perform phagocytosis of the microbes.
• Some of these proteins trigger the maturation of monocytes into macrophages, thereby increasing their numbers.
• Another protein interleukin-1 signals the brain to raise the body temperature, producing fever.
• Some other proteins also stimulate the specific immune response.
• Macrophages also play an essential role in wound healing and tissue repair by removing dead cells and debris.
• Dendritic cells (DCs) are found in tissue that has contact with the outside environment.
• They become antigen-presenting cells (APCs) that capture, process, and present antigens to lymphocytes to initiate and regulate the adaptive immune response.
• The main function of dendritic cells is the activation of T cells, whereas macrophages remove apoptotic cells and microbes by phagocytosis.

Neutrophils

• These belong to the granulocyte type of WBCs.
• They are highly short-lived and highly mobile as they squeeze between cells of capillary walls and can enter parts of tissue where other cells would not be able to enter otherwise.
• They move like Amoeba forming pseudopodia.
• They proceed rapidly to infected area to perform their duty and they often die after a single phagocytic event.
• Neutrophils also release lysosomal enzymes by extracellular degranulation that kill microorganisms and cause inflammation.
• Neutrophils can release Neutrophil extracellular trap to kill microbes.

Do You Know?

Dendritic cells, macrophages, and B-cells can function as antigen-presenting cells (APCs).

Summary Table of Phagocytic Cells

Intermediate Level

Phagocytic Cells

Monocytes

Macrophages

Dendritic Cells

Neutrophils

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Phagocytes are white blood cells.
• 2. They destroy abnormal cells or microbes.
• 3. They do so by engulfing.
• 4. This process is called phagocytosis.
• 5. Main types: macrophages, dendritic cells, neutrophils.
• 6. Monocytes are formed in bone marrow.
• 7. Monocytes circulate in blood for 1-3 days.
• 8. Monocytes migrate into tissues.
• 9. Monocytes become macrophages or dendritic cells.
• 10. Macrophages are found in organs.
• 11. Macrophages trap and destroy microorganisms.
• 12. Macrophages present antigens.
• 13. Macrophages secrete proteins.
• 14. Interleukin-1 signals the brain to raise body temperature.
• 15. Macrophages help in wound healing.
• 16. Dendritic cells are found in tissues with contact with outside environment.
• 17. Dendritic cells present antigens.
• 18. Dendritic cells activate T cells.
• 19. Neutrophils are granulocytes.
• 20. Neutrophils are short-lived and highly mobile.
• 21. Neutrophils release lysosomal enzymes.
• 22. Neutrophils can release Neutrophil extracellular trap.

Remember

• - Phagocytes = white blood cells that engulf and destroy
• - Phagocytosis = process of engulfing and destroying
• - Main types = macrophages, dendritic cells, neutrophils
• - Monocytes = formed in bone marrow; become macrophages or dendritic cells
• - Macrophages = found in organs; engulf and destroy microbes
• - Dendritic cells = found in tissues; antigen-presenting cells
• - Neutrophils = granulocytes; short-lived; highly mobile; release lysosomal enzymes

Common Mistakes

• 1. Confusing the three types of phagocytes — Macrophages, dendritic cells, neutrophils.
• 2. Mixing up the functions — Macrophages: engulf and destroy; dendritic cells: antigen presentation; neutrophils: engulf and destroy.
• 3. Forgetting the origin of macrophages — Monocytes.
• 4. Mixing up the locations — Macrophages: organs; dendritic cells: tissues; neutrophils: blood.
• 5. Forgetting the role of interleukin-1 — Signals the brain to raise body temperature.
• 6. Mixing up the roles — Macrophages: wound healing; dendritic cells: T cell activation.
• 7. Forgetting the role of neutrophils — Release lysosomal enzymes.
• 8. Believing phagocytes are not important — They are essential for defence.
• 9. Mixing up the types of WBCs — Neutrophils are granulocytes.
• 10. Thinking phagocytes only engulf microbes — They also present antigens.

Quick Revision

There are white blood cells in the body called phagocytes. A phagocyte is a cell that destroys other abnormal body cells (cancerous cells) or invaded microorganisms by engulfing. This process is called phagocytosis. Main types of phagocytic white blood cells are: macrophages, dendritic cells, and neutrophils. Monocytes are formed in bone marrow. From bone marrow, monocytes typically circulate in the blood for 1-3 days before migrating into tissues, where they become macrophages or dendritic cells. Macrophages are generally found in the organs such as the lungs, liver, spleen, kidney and lymph nodes. In these organs, they patrol within the free spaces among the cells and provide protection by trapping and destroying microorganisms entering the tissue. As macrophages interact with microbes, they not only engulf and destroy them; they also display some parts of microbes on their surface so that other body cells may also be informed. Such cells are called Antigen Presenting Cells (APCs). Dendritic cells (DCs) are found in tissue that has contact with the outside environment. They become antigen-presenting cells (APCs) that capture, process, and present antigens to lymphocytes to initiate and regulate the adaptive immune response. Neutrophils belong to the granulocyte type of WBCs. They are highly short-lived and highly mobile. Neutrophils also release lysosomal enzymes by extracellular degranulation that kill microorganisms and cause inflammation.

60-Second Revision

• Phagocytes = white blood cells that engulf and destroy
• Phagocytosis = process of engulfing and destroying
• Main types = macrophages, dendritic cells, neutrophils
• Monocytes = formed in bone marrow; become macrophages or dendritic cells
• Macrophages = found in organs; engulf and destroy microbes
• Dendritic cells = found in tissues; antigen-presenting cells
• Neutrophils = granulocytes; short-lived; highly mobile; release lysosomal enzymes
• Warning: Macrophages and dendritic cells are antigen-presenting cells

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• 9. Immunity

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• 9.2.2 PROTECTIVE PROTEINS OF COMPLEMENT SYSTEM

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