Chapter 16: Innate Immunity - Part 2

Overview

• The immune system defends against infectious diseases and cancer.
• Innate Immune Response (nonspecific):
  • First Line of Defense: Barriers, washing processes, chemical factors, microbiota.
  • Second Line of Defense: Activates if microbes breach the first line.
• Adaptive Immune Response (specific): Targets specific microbes actively infecting the body.

Second Line of Defense

• Activated when microbes penetrate the first line.
• Involves white blood cells (leukocytes) and processes such as inflammation, fever, and antimicrobial substances (complement and interferon).

Leukocytes

• Granule Sites: Granules in cytoplasm (e.g., eosinophils, basophils, neutrophils).
• Agranule Sites: Few granules, includes lymphocytes and monocytes (immature macrophages).

Phagocytosis

• Stages: Chemotaxis, adherence, ingestion, digestion, ejection.
• Carried out by neutrophils and macrophages.
• Process similar to human eating behavior but on a cellular level.

Inflammation

• Response to tissue damage (with or without infection).
• Benefits: Confines microbes, destroys them, facilitates tissue repair.
• Signs: Redness (ruber), heat (calor), swelling (tumor), pain (doler).
• Process:
  1. Injury stimulates release of histamine from damaged cells and mast cells.
  2. Histamine causes vasodilation and increased permeability of blood vessels.
  3. Neutrophils and plasma leak out to fight infection.
  4. Pus formation and clotting aid in containing infection.

Fever

• Elevated body temperature as a response to infection.
• Benefits:
  • Inhibits microbe replication and nutrient uptake.
  • Stimulates leukocyte activity.
• Process: Macrophages ingest microbes, release IL-1, which stimulates the hypothalamus to raise body temperature.

Complement System

• Group of serum proteins in blood.
• Activated in a cascade manner through three pathways:
  • Classical Pathway: Antibodies bound to microbe activate complement proteins.
  • Alternative Pathway: Complement proteins bind directly to microbes.
  • Lectin Pathway: Lectin binds to microbes to activate complement proteins.
• Outcomes of Complement Activation:
  • Opsonization: Proteins coat microbes, aiding phagocytosis.
  • Trigger Inflammation: Stimulates release of histamine.
  • Membrane Attack Complex (MAC): Lysis of microbes by forming pores in their membrane.

Interferons

• Type of cytokine, antiviral function, part of nonspecific immune response.
• Function: Protects uninfected cells by stimulating them to produce antiviral proteins.
• Process: Infected cells release interferons, which signal neighboring cells to produce antiviral proteins.