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.