Immunity updated full set

Immunology Notes

Overview of Immunology

  • Immunology: The study of the immune system, focusing on the protection of the body against foreign substances and organisms.
    • Two Main Types of Immunity:
    • Innate (Non-Specific) Immunity
      • General immunity present from birth, including barriers to infection and immune cells.
    • Acquired (Specific) Immunity
      • Develops after exposure to a specific pathogen; can take time to build up.

Innate Immunity

General Characteristics
  • Features:
    • Phagocytosis: The process by which phagocytes ingested and digest pathogens.
    • Destruction by Acid Secretions: Example: HCl in the stomach kills microorganisms.
    • Skin Resistance: Integrity of skin acts as a barrier to invasion.
    • Species Specificity: Certain species are resistant to some infections greater than others.
First Line of Defense

  • Physical Barriers:

    • Skin and Mucous Membranes:
    • Provide physical protection.
    • Epidermis Structure: Thick skin layer forming a barrier.
    • Mucous Secretion:
    • Acidity of skin secretions inhibits bacterial growth.
    • Sebum: Contains chemicals toxic to bacteria.
    • Hydrochloric Acid (HCl) & Pepsin in Stomach: Kill microorganisms.
    • Saliva and Lacrimal Fluid: Contain lysozyme, an enzyme that destroys bacteria.
    • Mucus: Traps microbes in respiratory passages.

  • Commensal Bacteria:

    • Naturally found on skin and in mouth, throat, and colon.
    • Inhibit the growth of harmful pathogens.
Continued First Line of Defense
  • Tears:
    • Contain lysozyme, an effective bactericidal enzyme; also found in other secretions (saliva, nasal, intestinal).
  • Sweat:
    • Contains salt, which inhibits bacterial growth.
  • Flushing Action of Urine:
    • Prevents establishment of bacteria.
  • Acidity of Vaginal Secretions:
    • Helps prevent infections by maintaining a low pH.

Second Line of Defense

  • Components:
    • Antimicrobial Substances:
    • Phagocytosis: Process by which cells ingest and digest pathogens.
    • Inflammation: The body's response to injury or infection, characterized by redness, swelling, heat, and pain.
    • Natural Killer (NK) Cells: Attack and destroy virus-infected or cancerous cells.
Antimicrobial Substances

  1. Interferons:

    • Definition: Proteins released from virus-infected cells that protect uninfected cells.
    • Function: Induce synthesis of antiviral proteins; interfere with viral replication.
    • Types: α, β, γ interferons.
    • Source: Dendritic cells, T cells, monocytes, fibroblasts, and epithelial cells.
    • Additional Function: Inhibiting tumor development.

  2. Complement Proteins:

    • A group of inactive proteins in plasma that, when activated, enhance immune reactions, including:
      • Cytolysis of Microbes: Killing microbes.
      • Promotion of Phagocytosis: Enhancing the ability to engulf pathogens.
      • Contribution to Inflammation.

  3. Transferrin:

    • An iron-binding protein that reduces available iron, limiting bacterial growth.
    • Sequesters iron into the liver and spleen during fever.

  4. Antimicrobial Proteins:

    • Short peptides with antimicrobial activity that kill microbes and attract immune cells. Examples include:
      • Dermicidins: From sweat glands.
      • Defensins & Cathelicidins: Produced by neutrophils, macrophages, and epithelium.
      • Thrombocidin: From platelets.
Phagocytosis
  • Major Phagocytes:
    • Neutrophils: Can ingest 5 – 20 bacteria, enter in response to chemotaxis.
    • Macrophages: Develop from monocytes; can engulf over 100 bacteria and also clear residual products.
  • Phagocytosis Process:
    • Stages:
    1. Chemotaxis: Attraction to pathogens via signaling substances.
    2. Adherence: Binding to pathogens.
    3. Ingestion: Engulfing pathogens.
    4. Digestion: Using enzymes to break down the microbe.
    5. Killing: Further destruction of the microorganism.
Factors Enhancing Phagocytosis
  • Presence of rough surface on pathogens, lack of a protective protein coat, adherence to antibodies & complement proteins (opsonization).
  • Diapedesis: The movement of phagocytes out of blood vessels into tissue.
  • Amoeboid Motion & Chemotaxis: Movement towards chemical signals from pathogens.

Chemotaxis

  • Definition: The movement of phagocytes (neutrophils and macrophages) toward chemical signals emitted from infected or damaged tissues.
  • Chemotactic Agents Include:
    • Bacterial Toxins: From pathogens.
    • Degenerative Products: From inflamed tissues.
    • Complement Components: Like C5a.
    • Polypeptides: From lymphocytes and mast cells.

The Immune Response

  • Acquired Immunity: Specific immunity developed after exposure:
    • B Cell (Humoral) Immunity: Produces antibodies, activates the complement system, neutralizes antigens. Major defense against bacterial infections.

- T Cell (Cell-Mediated) Immunity: Destroys infected cells; key defense against viruses and tumors.