9.2 Second Line of Defence - Nonspecific Defence

If microbes become successful to penetrate the skin or mucous membranes, then a second line of defence takes action against these foreign invaders. The second line of defence comprises three nonspecific internal defence mechanisms: phagocytic cells and natural killer cells, the inflammatory response, and fever. In addition, some protective proteins are also part of the second line of defence. These defences are nonspecific because they attack a wide variety of microbes, rather than targeting specific invaders as the immune response does.

Definition

Second Line of Defence: If microbes become successful to penetrate the skin or mucous membranes, then a second line of defence takes action against these foreign invaders. The second line of defence comprises three nonspecific internal defence mechanisms.

Nonspecific Defence: These defences are nonspecific because they attack a wide variety of microbes, rather than targeting specific invaders as the immune response does.

Main Idea

• If microbes penetrate the skin or mucous membranes, the second line of defence takes action.
• The second line of defence comprises three nonspecific internal defence mechanisms:
• In addition, some protective proteins are also part of the second line of defence.
• These defences are nonspecific because they attack a wide variety of microbes.
• They do not target specific invaders as the immune response does.

Core Concept

• Second line of defence = nonspecific internal defence
• Three mechanisms = phagocytic cells and natural killer cells; inflammatory response; fever
• Protective proteins = part of second line of defence
• Nonspecific = attack a wide variety of microbes
• Specific = targets specific invaders (third line of defence)
• Phagocytic cells = macrophages, dendritic cells, neutrophils
• Natural killer cells = attack cancerous and virus-infected cells
• Inflammatory response = response to tissue damage
• Fever = elevated body temperature

Detailed Explanation

Second Line of Defence - Nonspecific Defence

• If microbes become successful to penetrate the skin or mucous membranes, then a second line of defence takes action against these foreign invaders.
• The second line of defence comprises three nonspecific internal defence:
• In addition, some protective proteins are also the part of second line of defence.
• These defence are nonspecific because they attack wide variety of microbes, rather than targeting specific invaders as the immune response does.

Summary Table of Second Line of Defence

Summary of the Second Line of Defence

Intermediate Level

Second Line of Defence

Summary of the Second Line of Defence

Comparison of Second and Third Lines of Defence

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Second line of defence takes action if microbes penetrate skin or mucous membranes.
• 2. It comprises three nonspecific internal defence mechanisms.
• 3. First mechanism: phagocytic cells and natural killer cells.
• 4. Second mechanism: inflammatory response.
• 5. Third mechanism: fever.
• 6. Protective proteins are also part of second line of defence.
• 7. These defences are nonspecific.
• 8. They attack a wide variety of microbes.
• 9. They do not target specific invaders.
• 10. Specific invaders are targeted by the immune response (third line).
• 11. Phagocytic cells engulf and destroy microbes.
• 12. Natural killer cells attack cancerous and virus-infected cells.
• 13. Inflammatory response is provoked by invasion of microbes.
• 14. Fever is often produced.
• 15. Second line of defence is essential for controlling infection.

Remember

• - Second line of defence = nonspecific internal defence
• - Three mechanisms = phagocytic cells and natural killer cells; inflammatory response; fever
• - Protective proteins = part of second line of defence
• - Nonspecific = attack a wide variety of microbes
• - Specific = targets specific invaders (third line of defence)
• - Phagocytic cells = macrophages, dendritic cells, neutrophils
• - Natural killer cells = attack cancerous and virus-infected cells
• - Inflammatory response = response to tissue damage
• - Fever = elevated body temperature

Common Mistakes

• 1. Confusing second and third lines of defence — Second = nonspecific; third = specific.
• 2. Mixing up the mechanisms — Phagocytic cells, NK cells, inflammation, fever, protective proteins.
• 3. Forgetting the role of protective proteins — Part of second line of defence.
• 4. Thinking the second line of defence is specific — It is nonspecific.
• 5. Mixing up the action — Attacks wide variety of microbes.
• 6. Forgetting the role of phagocytic cells — Engulf and destroy microbes.
• 7. Mixing up NK cells — Attack cancerous and virus-infected cells.
• 8. Believing inflammation is not important — It is a key defence mechanism.
• 9. Mixing up fever and inflammation — Fever = elevated temperature; inflammation = response to tissue damage.
• 10. Thinking the second line of defence is not important — It is essential for controlling infection.

Quick Revision

If microbes become successful to penetrate the skin or mucous membranes, then a second line of defence takes action against these foreign invaders. The second line of defence comprises three nonspecific internal defence: First, the body has a standing army of phagocytic cells and natural killer cells. Second, invasion of microbes provokes an inflammatory response. Third, the body often produces fever. In addition, some protective proteins are also the part of second line of defence. These defence are nonspecific because they attack wide variety of microbes, rather than targeting specific invaders as the immune response does.

60-Second Revision

• Second line of defence = nonspecific internal defence
• Three mechanisms = phagocytic cells and natural killer cells; inflammatory response; fever
• Protective proteins = part of second line of defence
• Nonspecific = attack a wide variety of microbes
• Specific = targets specific invaders (third line of defence)
• Phagocytic cells = macrophages, dendritic cells, neutrophils
• Natural killer cells = attack cancerous and virus-infected cells
• Inflammatory response = response to tissue damage
• Fever = elevated body temperature
• Warning: Second line of defence is nonspecific; third line is specific

NEXT TOPIC

• Chapter:
• 9. Immunity

• Topic:
• 9.2.1 KILLING CELLS OF BLOOD

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