Overview of the Immune Response

Introduction

• The immune response consists of multiple parts: nonspecific and specific responses.
• This overview summarizes the entire immune response.

Stages of Immune Response

1. Inflammation

• Primary Defenses: Skin, sebum, mucus, scabs, stomach acid.
• If Pathogens Enter: Inflammation is the first response.
  • Mast Cells Activation: Release histamines and cytokines.
  • Effects of Histamines: Vasodilation and increased permeability.
    • Symptoms: Localized heat, redness, swelling, pain.
  • Cytokines: Attract phagocytes.

2. Phagocytosis

• Types of Phagocytes: Neutrophils and macrophages.
  • Neutrophils: Lobed nucleus, squeeze through blood vessel gaps, perform phagocytosis quickly.
  • Macrophages: Larger round nucleus, stay in bloodstream, become antigen-presenting cells (APCs).
  • Both contain lysosomes with hydrolytic enzymes (lysozymes).

Phagocytosis Process

• Engulfment of Pathogen: Form vesicle called phagosome.
• Fusion with Lysosome: Forms phagolysosome.
• Digestion: Pathogen digested except for antigens.
• Antigen Presentation: Antigens combined with MHC and presented on cell surface.
• Role of Opsinins: Tag pathogens for easier recognition.

3. Cell-Mediated Response

• T Lymphocytes: Made in bone marrow, mature in thymus.
  • Types of T Cells: T-helper, T-killer, T-regulatory, T-memory.
  • Activation of T-helper cells: Recognize antigen-MHC complex using CD4 receptor, release interleukins.
• Interleukins: Signal other cells, trigger mitosis and specialization.
  • T-Killer Cells: Release perforin and hydrogen peroxide to kill infected cells.
  • T-Regulatory Cells: Suppress immune response to prevent autoimmunity.
  • T-Memory Cells: Responsible for immunological memory.

4. Humoral Response

• B Lymphocytes: Made and mature in bone marrow.
  • Clonal Selection: Selection of B cells with specific antibodies.
  • Clonal Expansion: Mitosis to produce B plasma cells and B memory cells.
• B Plasma Cells: Produce specific antibodies.
• B Memory Cells: Provide immunological memory.

Antibodies (Immunoglobulins)

• Structure: Y-shaped, heavy chains, light chains, variable regions, constant regions.
• Functions:
  • Agglutination: Clump pathogens for easier phagocytosis.
  • Opsinization: Tag pathogens.
  • Neutralization: Bind to toxins and neutralize them (antitoxins).

Ending Immune Response

• T-Regulatory Cells: Kill active white blood cells except memory cells to prevent overreaction (autoimmunity).
• Memory Cells: Stay in the bloodstream to respond faster upon re-exposure to the same pathogen.

Summary

• Initial Infection: Pathogens enter, inflammation occurs, phagocytosis begins.
• Antigen Presentation: Macrophages present antigens, trigger specific immune response.
• Specific Response: T and B cells activated, clonal selection and expansion, antibodies produced.
• Memory: Memory cells remain, providing faster response upon re-exposure.