Non-specific & Specific Immune Defenses Study Notes

Unit 3 pt 2: Non-specific & Specific Immune Defenses

The Immune System

The 3 Levels of Defense Mechanisms

1. First Line of Defense: Innate and nonspecific barriers that serve as the first line of protection against pathogens.

   • Physical Barriers:

     • Skin

     • Mucous membranes

     • Cilia

   • Chemical Defenses:

     • Lysozymes in tears and saliva

     • Fatty acids

     • Gastric enzymes

2. Second Line of Defense: Innate immune response involving immune cells that react to pathogens.

   • Phagocytes

     • Example: Macrophages and neutrophils
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3. Third Line of Defense: Adaptive immune response characterized by lymphocyte activity.

   • Lymphocytes

     • T cells

     • B cells

First Line of Defense: Innate, Nonspecific Barriers at the Portal of Entry

• The first line consists of various physical and chemical barriers that prevent pathogen entry, notably:

  1. Physical Barriers:

     • Skin: The largest organ; acts as a physical barrier

     • Mucous membranes: Line the body cavities and secrete mucus

     • Cilia: Hair-like structures that move mucus out of the respiratory tract

  2. Chemical Defenses:

     • Fatty acids secreted by sebaceous glands, impacting skin pH.

     • Lysozymes: Enzymes found in tears and saliva; hydrolyze peptidoglycan, a component of bacterial cell walls, effective against Gram-positive bacteria.

     • Gastric enzymes: Part of the acidic environment in the stomach that kills pathogens

Primary Defense Barriers

• Sebaceous Glands: Secrete sebum, a fatty substance that lowers skin pH, creating an inhospitable environment for many pathogens.

• Tears: Contain lysozyme, aiding in the breakdown of bacteria.

• Wax: Found in various body orifices, trapping pathogens.

• Mucus: Provides a barrier and traps pathogens.

• Sweat: Contains antimicrobial peptides.

• Defecation & Urination: Mechanisms to physically expel pathogens.

• Stomach Acid: Destroys pathogens ingested with food.

• Intestinal Enzymes: Help in breaking down pathogens in the digestive tract.

Chemical Barriers

• Sebum and Lysozyme Analysis:

  • Sebum: Creates a lower skin pH, protective barrier.

  • Lysozyme: Destroys peptidoglycan, effective against Gram-positive bacteria.

  • Bile: Solubilizes fats, neutralizing bacterial growth.

Mucus Membranes

• Mucous membranes cover physical barriers and line body cavities.

• Respiratory Tract: Cells within the respiratory tract possess cilia and mucus cells, which help trap and expel pathogens.

Chemical Barriers Continued: Interferon and Complement System

1. Interferon:

   • Triggers cells to produce protective proteins against viruses.

   • Inhibits viral spread and promotes resistance to infections.

   • Function: Produced in response to viral RNA; interferon changes host cell metabolism to degrade viral mRNA, inhibiting replication.

2. Complement System:

   • Comprising over 20 proteins produced in the liver, involved in both innate and adaptive immunity. exceptional complex system

   • Functions:

     • Opsonization: Marks pathogens for phagocytosis.

     • Inflammation Regulation: Mediates inflammatory response.

     • Microbial Lysis: Forms membrane attack complexes, leading to cell death.

Mechanisms of Complement Activation

• The complement activation follows two pathways:

  1. Alternative Pathway: Functions as part of innate immunity, responding to pathogens directly.

  2. Classical Pathway: Part of the adaptive immune response activated by antibodies.

Other Effects of Complement Activation

• Inflammation: Increases blood vessel permeability and attracts phagocytes to the site of infection.

• Opsonization: Facilitates immune adherence of pathogens to phagocytes.

• Cytolysis: Causes the loss of cellular contents through the transmembrane channel formed by the membrane attack complex (MAC).

Innate Immune Cells and Their Functions

• Phagocytes: Including dendritic cells, macrophages, and neutrophils, which play crucial roles in detecting and responding to pathogens.

  • Dendritic Cells: Phagocytize small bits of pathogens and present antigens to T cells.

  • Macrophages: Capable of engulfing large amounts of pathogens and dead cells.

  • Neutrophils: Efficiently track down and eliminate microbes.

Phagocytic Response and Inflammatory Reaction

1. Inflammatory Response:

   • Critical second line of defense when pathogens invade.

   • Involves release of histamines from damaged tissues, increasing blood flow to the area and causing vessel permeability enhancements.

   • Symptoms include pyrexia (fever), erythema (redness), edema (swelling), and pain.

2. Role of Histamine: Increases blood flow, allowing phagocytes and other immune factors to access the injured area.

3. Platelet Activity: Platelets move out of capillaries to form clots, sealing the area and preventing further loss of blood and entry of pathogens.

Role of Natural Killer (NK) Cells

• NK cells can recognize cells infected by viruses or cancer cells, as they lack normal peptide fragments usually presented on cell surfaces, marking them for destruction.

Summary of Innate Immune Response

• Phagocytosis by macrophages and dendritic cells acts as a bridge to adaptive immunity, priming the body for a more targeted immune response in future encounters with pathogens.

Visualization of Immune Defense Mechanisms

1. Physical Barriers:

   • Prevent access of pathogens.

2. Phagocytes:

   • Remove debris and pathogens from the body.

3. Immunological Surveillance:

   • Identifies and destroys abnormal cells.

4. Inflammatory Response:

   • Multi-faceted effect involving the elevation of regional temperature, activation of phagocytes, and increase in vascular permeability.

5. Fever:

   • Mobilizes defenses, accelerates repairs, and inhibits pathogen replication.

Summary Points

• The innate immune system provides immediate and generalized responses to pathogens while establishing a foundation for the adaptive immune system that targets specific pathogens more efficiently.