lecture recording on 22 January 2025 at 18.45.25 PM

Overview of Immunity

• Immunity is essential for understanding concepts surrounding microbial genesis and polyclonality.

• Importance of optimal immunity: maintaining health and preventing illness.

Types of Immunity

Innate Immunity

• Innate (or nonspecific) immunity: provides general protection against pathogens.

• First line of defense: physical barriers including skin and mucous membranes.

• Examples:

  • Skin: A barrier; breaks in the skin increase infection risk.

  • Mucous membranes: Ciliated cells in the GI and respiratory tract aid expulsion of foreign particles.

  • Normal flora: Beneficial organisms that prevent pathogenic proliferation but can become pathogenic under certain circumstances.

Adaptive Immunity

• Adaptive (or acquired) immunity: specific response tailored to particular pathogens.

• Requires initial response from innate immunity for effectiveness.

• Involves lymphocytes:

  • B lymphocytes (B cells): Responsible for antibody production.

  • T lymphocytes (T cells): Assist in targeting specific pathogens.

    • Helper T cells (CD4): Activate B cells and cytotoxic T cells.

    • Cytotoxic T cells (CD8): Directly attack infected cells.

Immune Response Mechanism

Antigens

• Recognized as foreign substances in the body, provoking an immune response.

• Antigens are identified by cells and presented to immune cells for a targeted response.

Innate Immune Response

First Line of Defense

• Physical and chemical barriers:

  • Skin, tears, saliva, natural flora in the gut.

Second Line of Defense

• Comprised of nonspecific responses involving:

  • Neutrophils and macrophages mobilizing to site of infection.

  • Inflammation: key components include redness, swelling, heat, pain, and loss of function.

    • Increases blood flow and allows cells to reach the affected area.

• Cytokines: Signaling proteins that coordinate the inflammatory response and recruit more immune cells.

Phagocytosis

• Process by which immune cells, like macrophages and neutrophils, engulf and destroy pathogens.

• Involves four steps:

  • Margination: White blood cells adhere to blood vessel walls.

  • Transmigration: Cells exit the bloodstream and enter tissue.

  • Chemotaxis: Movement toward higher concentrations of signaling molecules.

  • Engulfment: Phagocytes internalize and digest the pathogen.

Adaptive Immune Response

Cellular Immunity

• T cells play a crucial role:

  • Helper T cells (CD4): Activate other immune cells and initiate antibody production by B cells.

  • Cytotoxic T cells (CD8): Target and kill infected or abnormal cells.

Humoral Immunity

• B cells transform into plasma cells that produce antibodies in response to specific antigens:

  • Antibodies: Proteins that bind to antigens, marking them for destruction and neutralization.

  • Subtypes:

    • IgG: Main type of antibody; involved in long-term immunity.

    • IgM: First antibody produced in response to infection.

    • IgA: Found in mucosal areas; provides protection at entry points of pathogens.

    • IgE: Associated with allergic reactions and responses to parasites.

Memory Cells

• B and T cells can become long-lasting memory cells after activation, providing quicker and more robust responses to subsequent exposures to the same antigen.

Importance of Homeostasis

• The immune system is constantly balancing between attacking pathogens and tolerating self-components.

• Disorders can result from a breakdown in these processes, leading to autoimmunity or hypersensitivity reactions.

Summary of Inflammation and Immune Interactions

• Complement System: Enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells.

• Mast Cells: Release histamine and other mediators during inflammation, contributing to allergic responses.

• Cardinal Signs of Inflammation: Redness, swelling, heat, pain, and loss of function signal an active immune response depending on the nature of the insult.