BY 312 Lecture (3/27)

Overview of the Immune System

Innate Immunity

  • Phagocytes and Phagocytosis

    • Discussion on the role of phagocytes, particularly wandering and mixed macrophages, in innate immunity.

    • Phagocytosis involves several steps:

    1. Chemotaxis: Chemically stimulated movement of phagocytes toward damaged tissues, facilitated by chemicals produced by microbes.

    2. Adherence: Attachment of phagocytes to microbes or foreign materials.

    3. Ingestion: Phagocytes use pseudopods to engulf and internalize microbes, forming a phagosome.

    4. Digestion: Merging of the phagosome with lysosomes creates a phagolysosome, where microorganisms are broken down.

    5. Killing Phase: Remaining indigestible material is termed a residual body, which is then recycled.

  • Natural Killer Cells: Discussion on these cells' role in innate immunity, especially in relation to phagocytosis.

  • Endogenous Antimicrobials (AMPs): These antimicrobial proteins are produced by neutrophils and macrophages to assist in the immune response.

    • Defensins: A well-known type of AMP exhibiting broad-spectrum antimicrobial activity.

  • Complement System:

    • Described as a group of inactive proteins that, once activated, enhances immune reactions by attacking cell walls, attracting phagocytes, and stimulating inflammation.

  • Iron Binding Proteins: Inhibit bacterial growth by reducing available iron.

  • Interferons: Proteins released by virus-infected cells that activate immune responses to prevent viral replication.

    • Types of interferons discussed: alpha, beta, and gamma.

Phagocytosis Revisited

  • Detailed steps of phagocytosis re-emphasized, linking to previous discussions and emphasizing critical processes like oxidative bursts and the creation of residual bodies.

Fever and Inflammation

Fever

  • Defined as an abnormally high body temperature caused by resetting the hypothalamic thermostat.

    • Functions of fever include:

    • Speeding up body reactions.

    • Enhancing the effects of endogenous antimicrobials.

    • Mobilization of defenses and acceleration of tissue repair.

    • Inhibition of pathogens.

Inflammation

  • A generalized defensive response to tissue damage from various causes (infections, burns, cuts).

  • Common signs of inflammation:

    • Redness (increased blood flow)

    • Pain (chemical stimulation of pain receptors)

    • Heat (due to increased blood flow)

    • Swelling (fluid accumulation at the site)

Stages of Inflammation

  • Three basic stages of inflammation:

    1. Vasodilation: Increases blood flow and permeability.

    2. Emigration: Movement of phagocytes from blood vessels into interstitial spaces to site of damage.

    3. Tissue Repair: Involves removal of toxins and debris, and re-establishment of normal tissue function.

Additional Inflammatory Mediators

  • Mention of histamines, kinins, prostaglandins, leukotrienes, and complements as crucial players in the inflammatory response.

  • Role of kinins in chemotaxis.

  • Prostaglandins enhance other mediators.

Sensitization and Pain

  • Pain as a key signal for inflammation, helping to alert the body of injury.

  • Importance of pain in promoting protective behavior (avoiding further harm).

Types of Inflammation

  • Acute Inflammation: Rapid onset, lasts days to weeks, characterized by immediate response to tissue damage.

  • Chronic Inflammation: Slow, prolonged response lasting months or years, exemplified by conditions like rheumatoid arthritis and peptic ulcers.

    • Chronic inflammation can lead to continued pain and immobility due to sensitization of nerve endings.

Summary of Key Concepts

Immune Response

  • Review of components involved in innate immunity, including:

    • AMPs,

    • Natural killer cells,

    • Complement system,

    • Iron binding proteins, and interferons.

Transition to Adaptive Immunity

  • Introduction to adaptive immunity, defined as the body's ability to specifically respond to foreign antigens.

  • Key characteristics of adaptive immunity include:

    • Specificity: Ability to distinguish between self and non-self through antigens (MHC).

    • Memory: Previously encountered antigens result in quicker and more vigorous immune responses during future attacks.

  • Definition of antigens as foreign substances that trigger an immune response, clarifying that not all foreign materials are antigenic.

  • Explanation of epitopes as specific sites on antigens that initiate immune responses.

  • Closure with emphasis on the significance of learning about both adaptive and acquired immune responses in future classes, hinting at an upcoming discussion on vaccines.