Immune Responses to Pathogens

Overview of the Immune System

• Immune System: A crucial entity that maintains homeostasis and defends against pathogens.
• Comprises two primary components:
  • Innate Immunity: A fast, non-specific defence that protects against various pathogens.
  • Adaptive Immunity: Provides targeted and long-lasting protection, by remembering specific pathogens.
• These systems operate together to ensure a comprehensive defence against diseases.

Key Terminology

• Pathogen: Microorganisms, including bacteria and viruses, that may cause disease.
• Antigen: Molecular structures identified by the immune system that induce an immune response.
• Immunity: The body's ability to resist harmful microbes or abnormal cells.
• Innate Immunity: The first line of defence, rapidly acting to protect against infections.
• Adaptive Immunity: Launches a precise response, customising defences against specific invaders and retaining memory for subsequent threats.

Physical Barriers of the Immune System

• Skin: Provides a defensive barrier with layers that prevent pathogen infiltration.
• Mucous Membranes: Capture pathogens. Cilia in respiratory passages help remove mucus and bacteria.
• Secretion: Tears and saliva contain antimicrobial enzymes to neutralise pathogens.
• Sphincters: Function as barriers to block pathogen entry.

Cellular Components of Innate Immunity

• Phagocytes:
  • Utilise surface markers to identify and ingest pathogens.

• Antigen-Presenting Cells (APCs):
  • Display antigens to initiate adaptive immunity.

Inflammatory and Immune Responses

Inflammatory Response

• Scenario: When a splinter occurs, the affected area becomes red and swollen due to inflammation.
• Steps of Inflammation:
  • Capillary Widening: Enhances blood flow.
  • Increased Blood Flow: Delivers immune cells.
  • White Blood Cell Migration: Concentrates at the infection site.
• Key Chemicals: Histamines, Bradykinins, Cytokines, Chemokines facilitate inflammation.

Role of Natural Killer Cells (NK Cells)

• Function Example: NK cells identify and eliminate virus-infected or cancerous cells.
• Mechanisms of Action: Release cytotoxic chemicals.

Differentiating Innate and Adaptive Immunity

• Innate Immunity: The body's general defence, acting immediately through physical barriers and inflammation.
• Adaptive Immunity:
  • Specificity and Memory Formation:
    • Targets specific antigens with memory cells.
    • Analogy: Like recognising a familiar voice in a crowd.

Mechanisms of the Adaptive Immune Response

Humoral Response

• B Lymphocytes:
  • Produce antibodies to neutralise pathogens.
  • Mnemonic: "Antibodies Act Swiftly."
• Antibody Diversity:
  • Antibody Arrays cover antigens comprehensively.

Cell-mediated Response

• T Lymphocytes:
  • Cytotoxic T Cells: Eliminate infected cells.
  • Helper T Cells: Activate immune cells through cytokines.

Clonal Selection and Memory Formation

• Clonal Selection Steps:
  1. Detection by specific B/T cells.
  2. Activated cells replicate to combat threats.
  3. Infected cell removal by replicated cells.

• Memory Cells: Retain pathogen knowledge for faster future responses.
  • Analogy: Like recognising a favourite song.

Influence of Vaccines

• Mechanism: Safely introduces antigens to stimulate antibody and memory cell production without causing disease.

Innate Immune Response Upon First Exposure

Detection of Pathogens

• PAMPs: Distinct patterns on pathogens identified by PRRs.

• TLRs: Detect PAMPs and initiate immune response.

Triggering Inflammatory Response

• Cytokines & Chemokines: Chemical signals that summon immune cells.
• Vasodilation: Increases blood flow to infected areas.

Adaptive Immune Response Following Initial Exposure

Antigen Presentation

• Dendritic Cells and Macrophages:
  • Present antigens like "wanted" signs to T cells.

Activation of T and B Cells

• Helper T cells (CD4+): Mobilise B and cytotoxic T cells.
• B cells: Produce antibodies.

Memory Cell Formation

• Memory B and T cells: Lead to a quick response upon reinfections.

Synergy and Signalling Pathways

Communication Pathways

• Cytokines:
  • Interleukins: Coordinate immune cell activities.
  • Interferons: Combat viral infections.

Additional Considerations

• Immune Tolerance: Mechanism that prevents the immune system from attacking the body's own cells, vital for healthy functioning.

Key Takeaways:

• The innate and adaptive systems collaborate seamlessly to combat pathogens.
• Effective system communication is essential for comprehensive immune protection.
• A thorough understanding of each component enhances preparedness for various threats.