IM

Immune System Overview

Immunity: An Overview

Introduction

  • The instructor admits immunity was a challenging subject for them due to its complexity and numerous chemical interactions.
  • The lecture aims to provide a core understanding of the immune system, but with less detail than some other courses.
  • Be cautious when studying this chapter in detail; it can quickly become deeply physiological.
  • The level of detail presented in the lecture should guide your study depth.

Definition of Immunity

  • Immunity, in the context of this course, refers broadly to anything involved in defense, not just specialized immune cells.
  • This includes physical barriers like the skin, which are considered part of the immune system because they help defend the body.

Key Terms

  • Pathogen: Anything that can cause disease or illness.
  • Antigen: Anything that triggers an immune response; typically foreign substances such as molecules on the surface of a bacterium.
  • Antibody: A specialized protein that carries out the immune response.
    • An antibody is part of the body's response, specifically a specialized protein that executes the immune response.

Antigen Example

  • If a bacterium has glycoproteins on its cell surface, any of these glycoproteins could act as an antigen.
  • Specialized cells recognize these antigens as foreign, triggering an immune response.

Division of the Immune System: Innate vs. Adaptive

Innate Defenses

  • Definition: Defenses we are born with; present at birth.
  • Example: Skin.
  • Innate defenses do not change significantly throughout life.
  • Characteristics:
    • Always present and ready to go.
    • Available rapidly; no preparation time needed.
    • No memory; the response is the same regardless of previous exposure.

Adaptive Defenses

  • Definition: Defenses that change and adjust over time.
  • Characteristics:
    • Slower responses; take time to prepare.
    • Specific to particular antigens.
    • Adaptive defenses against one bacteria do not protect against a different bacteria.
    • Learn and adapt from experience; possess memory.

Vaccination Example

  • Vaccinations teach the body to recognize and prepare for specific pathogens like the COVID virus.
  • They trigger the immune system without causing full disease, enabling a better and faster response upon actual infection.
  • The immune system may become so efficient that subsequent infections are asymptomatic.

Comparison of Innate and Adaptive Defenses

  • Innate: Born with, fast, general, no memory (e.g., skin).
  • Adaptive: Develops over time, slow, specific, has memory (e.g., vaccines).

Cells of the Immune System

  • Neutrophils and Macrophages: Part of innate immunity; recognize and engulf (phagocytize) any foreign material.
  • Lymphocytes: Part of adaptive immunity; have highly specialized receptors that bind to specific antigens.
  • Basophils and Mast Cells: Involved in the innate side of things, but they do not have phagocytic activity; they signal for help and damage.

Pathogens

  • Bacteria and viruses are different types of pathogens that can cause disease.
  • Bacteria are cells, while viruses are bits of genetic code with a protein coat.
  • Antibiotics are effective against bacteria but not viruses.

Focus of the Chapter: Immune Response

  • The immune response is the primary focus of the chapter.

Overview of the Immune System: Figure 24.1

  • Figure 24.1 is a crucial overview of the entire immune system.

First Line of Defense: Barriers

  • The first line of defense involves preventing pathogens from entering the body.
  • Barriers include:
    • Physical: Skin, hair.
    • Chemical: Antimicrobial enzymes in sebum and sweat, stomach acidity, vaginal acidity.
    • Mechanical: Urine flow, mucociliary escalator.

Innate Defenses: Internal

Phagocytosis

  • Generalized phagocytes (neutrophils, monocytes, macrophages) engulf and digest pathogens.

Natural Killer (NK) Cells

  • Related to lymphocytes but are generalists.
  • Recognize and target cancer cells, tumor cells, and viral-infected cells.

Inflammation

  • The body's normal response to tissue damage.
  • Triggers the healing process, despite unpleasant symptoms.
Basophils and Histamine
  • Basophils produce histamine, a crucial signaling molecule that triggers inflammation.
Symptoms of Inflammation
  • Heat and Redness: Result from increased blood flow (vasodilation) to the area.
  • Swelling (Edema): Caused by leaky capillaries and plasma proteins drawing fluid into the interstitium.
  • Pain: Nerve endings are compressed by swelling and chemically stimulated.
  • Loss of Function:
    • The fifth symptom of inflammation is loss of function.
    • Swelling and pain make it difficult to use the affected body part normally.
The Process of Inflammation
  • Tissue damage leads to the release of signaling chemicals (histamine, prostaglandins).
  • These chemicals cause vasodilation and increased permeability of local capillaries.
  • Increased blood flow brings heat and redness.
  • Increased permeability allows proteins into the interstitium, causing swelling.
  • Pressure and chemicals stimulate pain receptors, resulting in pain.

Anti-Inflammatory Drugs

  • Nonsteroidal anti-inflammatory drugs (NSAIDs) block the formation of signaling chemicals like prostaglandins, reducing inflammation.

Antimicrobial Proteins

  • Specialized proteins produced in response to pathogens.
Interferons
  • Defense against viruses.
  • Infected cells produce interferons, which interfere with viral replication in nearby cells.
  • Interferons bind to receptors on neighboring cells, activating their antiviral defenses.
Complement System
  • A series of proteins in the blood that, when activated, enhance body defenses.
Membrane Attack Complex (MAC)
  • A complex of complement proteins that creates a channel in the membrane of invading bacteria.
  • This channel allows ions and water to enter, causing the cell to swell and burst (lysis).

Summary of Innate Defenses

  • Innate defenses include surface barriers (skin, mucous membranes) and internal defenses (phagocytosis, NK cells, inflammation, antimicrobial proteins).
  • Antimicrobial proteins include interferons and the complement system.

Transition to Adaptive Defenses

  • The next lecture will cover adaptive defenses and specialized lymphocytes.