9.3 Third Line of Defence - the Specific Defences

If a pathogen is able to get past the body's nonspecific defence, the third line of defence interferes with a series of defence responses, often called immune responses that attack the particular pathogens having specific antigens. These antigens serve as the stimulus to produce an immune response. The term "antigen" comes from ANTIbody GENerating substances. Viruses, bacteria and other pathogen have specific antigens on their surface.

Definition

Third Line of Defence: If a pathogen is able to get past the body's nonspecific defence, the third line of defence interferes with a series of defence responses, often called immune responses that attack the particular pathogens having specific antigens.

Antigen: These antigens serve as the stimulus to produce an immune response. The term "antigen" comes from ANTIbody GENerating substances. Viruses, bacteria and other pathogen have specific antigens on their surface.

Main Idea

• Third line of defence is the specific defence.
• It interferes if a pathogen gets past the nonspecific defence.
• It involves a series of defence responses called immune responses.
• These responses attack particular pathogens having specific antigens.
• Antigens serve as the stimulus to produce an immune response.
• The term "antigen" comes from ANTIbody GENerating substances.
• Viruses, bacteria and other pathogen have specific antigens on their surface.
• The third line of defence respond against particular infections.
• It acts as the most powerful means of resisting infections.
• Its response can be of two types:
• These immune responses are particularly carried out by two components:
• Third line of defence also involves role of monocytes (macrophages) that participate in activation of these lymphocytes.

Core Concept

• Third line of defence = specific defence
• Immune responses = attack particular pathogens
• Antigens = specific molecules on pathogen surface
• Antigen = ANTIbody GENerating substance
• Types of immune response = humoral; cell-mediated
• B cells = humoral immune response
• T cells = cell-mediated immune response
• Monocytes (macrophages) = activate lymphocytes

Detailed Explanation

Third Line of Defence - The Specific Defences

• If a pathogen is able to get past the body's nonspecific defence, the third line of defence interferes with a series of defence responses, often called immune responses that attack the particular pathogens having specific antigens.
• These antigens serve as the stimulus to produce an immune response.
• The term "antigen" comes from ANTIbody GENerating substances.
• Viruses, bacteria and other pathogen have specific antigens on their surface.
• Since, the third line of defence respond against particular infections and acts as the most powerful means of resisting infections therefore, it is also called specific defence.
• Its response can be of two types:
• These immune responses are particularly carried out by two components:
• However, third line of defence also involves role of monocytes (macrophages) that participate in activation of these lymphocytes.

Summary Table of Third Line of Defence

Intermediate Level

Third Line of Defence

Types of Immune Response

Role of Monocytes

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Third line of defence is the specific defence.
• 2. It interferes if a pathogen gets past the nonspecific defence.
• 3. It involves immune responses.
• 4. Immune responses attack particular pathogens.
• 5. Pathogens have specific antigens.
• 6. Antigens serve as the stimulus.
• 7. "Antigen" comes from ANTIbody GENerating substances.
• 8. Viruses, bacteria and other pathogens have antigens.
• 9. Third line of defence responds against particular infections.
• 10. It is the most powerful means of resisting infections.
• 11. It is also called specific defence.
• 12. Response can be humoral or cell-mediated.
• 13. Humoral immune response is carried out by B cells.
• 14. Cell-mediated immune response is carried out by T cells.
• 15. Monocytes (macrophages) activate lymphocytes.
• 16. B-lymphocytes are also called B cells.
• 17. T-lymphocytes are also called T cells.
• 18. Third line of defence involves monocytes.
• 19. Monocytes participate in activation of lymphocytes.
• 20. Third line of defence provides long-lasting immunity.

Remember

• - Third line of defence = specific defence
• - Immune responses = attack particular pathogens
• - Antigens = specific molecules on pathogen surface
• - Antigen = ANTIbody GENerating substance
• - Types of immune response = humoral; cell-mediated
• - B cells = humoral immune response
• - T cells = cell-mediated immune response
• - Monocytes (macrophages) = activate lymphocytes

Common Mistakes

• 1. Confusing third line with first and second lines — Third = specific; first and second = nonspecific.
• 2. Mixing up B cells and T cells — B cells = humoral; T cells = cell-mediated.
• 3. Forgetting the role of antigens — Serve as stimulus.
• 4. Mixing up the types of immune response — Humoral and cell-mediated.
• 5. Forgetting the role of monocytes — Activate lymphocytes.
• 6. Believing the third line of defence is not important — It is the most powerful means of resisting infections.
• 7. Mixing up the terms — B-lymphocytes = B cells; T-lymphocytes = T cells.
• 8. Forgetting the origin of the term antigen — ANTIbody GENerating substances.
• 9. Thinking all pathogens have the same antigens — Antigens are specific.
• 10. Mixing up the functions — Humoral = antibodies; cell-mediated = direct cell attack.

Quick Revision

If a pathogen is able to get past the body's nonspecific defence, the third line of defence interferes with a series of defence responses, often called immune responses that attack the particular pathogens having specific antigens. These antigens serve as the stimulus to produce an immune response. The term "antigen" comes from ANTIbody GENerating substances. Viruses, bacteria and other pathogen have specific antigens on their surface. Since, the third line of defence respond against particular infections and acts as the most powerful means of resisting infections therefore, it is also called specific defence. Its response can be of two types: Humoral immune response and cell-mediated immune response. These immune responses are particularly carried out by two components: B-lymphocytes or B cells and T-lymphocytes or T cells. However, third line of defence also involves role of monocytes (macrophages) that participate in activation of these lymphocytes.

60-Second Revision

• Third line of defence = specific defence
• Immune responses = attack particular pathogens
• Antigens = specific molecules on pathogen surface
• Antigen = ANTIbody GENerating substance
• Types of immune response = humoral; cell-mediated
• B cells = humoral immune response
• T cells = cell-mediated immune response
• Monocytes (macrophages) = activate lymphocytes
• Warning: Third line of defence is specific; first and second lines are nonspecific

NEXT TOPIC

• Chapter:
• 9. Immunity

• Topic:
• 9.3.1 ROLE OF MONOCYTES IN THIRD LINE OF DEFENCE

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