New Recording 67

Immune System Overview

Introduction

  • The immune system has three lines of defense:

    • First line

    • Second line

    • Third line

  • Recall from previous discussions about the immune system.

First Line of Defense: Physical Barriers

Skin as a Barrier

  • The skin is likened to a castle with a moat preventing invaders from entering.

  • Key components of the skin's defense:

    • Sebum:

    • Oil secreted by sebaceous glands.

    • Contains antimicrobial proteins that help protect against pathogens.

    • Sweat:

    • Contains toxins that help kill pathogens.

  • Structure of Skin:

    • Composed of stratified squamous epithelial cells.

    • Presence of five strata with the stratum granulosum being significant because:

      • Contains keratohyalin granules which produce keratin to provide strength and water resistance.

      • Contains laminated granules that produce a glycolipid creating tight junctions between cells preventing penetration.

  • Continuous defense:

    • Skin is always working to prevent pathogen entry, functioning as the first line of defense 24/7.

Mucous Membranes as a Barrier

  • Mucous membranes in different body areas provide additional defenses:

    • Locations: Respiratory system, digestive tract, eyes, etc.

    • Protective functions:

    • Trap and filter bacteria.

    • Warm and moisture incoming air.

    • Lacrimal fluid contains enzymes that destroy bacteria in the eyes.

    • Ceruminous glands in ears produce earwax that traps bacteria akin to mucus.

  • Natural expulsion: Mucus traps debris which can be removed through sneezing, coughing, or other means.

  • Approximately 90% of encounters with pathogenic agents are managed by the first line of defense.

Second Line of Defense: Immune Response Activation

Components of the Second Defense

  • Once a pathogen breaches the first line, the second line mobilizes:

    • Phagocytic Cells:

    • Engulf and destroy pathogens.

    • Natural Killer Cells:

    • Attack and destroy virus-infected cells and cancer cells.

    • Antimicrobial Proteins:

    • Enhancements to the immune response.

    • Inflammation:

    • Localized reaction to injury or infection, leading to redness, heat, swelling, and pain.

    • Fever:

    • Elevated body temperature to hinder microbial growth.

  • These components act quickly to respond to invading pathogens and reduce the risk of infection.

Third Line of Defense: Adaptive Immune Response

Characteristics of the Third Line

  • Adaptive immunity involves lymphocyte response and memory:

    • B cells and T cells.

    • Slow to activate initially, but facilitate a stronger and quicker response upon subsequent exposures.

B Cells and Antibody Production

  • Humoral Immunity:

    • B cells produce antibodies that circulate in blood plasma to neutralize pathogens.

    • Mechanism of action involves targeting foreign invaders to reduce their effectiveness or eliminate them from the body.

T Cells and Cellular Immunity

  • Cellular Immunity:

    • T cells attack infected cells directly and release chemicals to enhance the immune response.

    • Types of T cells:

    • Cytotoxic T cells: Directly kill infected cells.

    • Helper T cells: Assist in activating B cells and other T cells.

Memory Cells

  • Following infection, some B and T cells differentiate into memory cells which persist in the body for faster response in subsequent infections.

    • Memory Cell Functionality: Rapid response upon re-exposure to the same pathogen.

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Immune System Activation

Selective Activation of Lymphocytes

  • T cells undergo selection to ensure they do not attack self-molecules:

    • Positive Selection: T cells must recognize self-MHC proteins.

    • Negative Selection: T cells that bind too strongly to self-antigens are eliminated.

  • Result is a pool of mature and educated lymphocytes ready to respond to foreign antigens.

Antigen Presentation

  • Antigen-Presenting Cells (APCs):

    • Dendritic cells, macrophages, and certain B cells help activate T cells by presenting processed antigens on their surface, enhancing the immune response.

Cytokines and Inflammation

  • Cytokines:

    • Signaling molecules released in response to infection, enhancing the overall immune response.

  • The immune system can be classified into two main categories: innate immunity and adaptive immunity.

Innate Immunity

  • Innate Immunity: Present at birth; provides the first line of defense against pathogens.

    • Non-specific responses against a wide range of pathogens.

    • Includes physical barriers (like skin), phagocytic cells, and antimicrobial proteins.

Adaptive Immunity

  • Adaptive Immunity: Develops over time as the body encounters different pathogens.

    • Specific Responses: Targeted responses against specific pathogens that the immune system has previously encountered.

    • Involves the creation of memory cells, which express faster and stronger responses after re-exposure.

Vaccination

  • Vaccines are designed to stimulate the adaptive immune response, causing the body to produce memory cells against specific pathogens without causing disease.

Autoimmunity

  • Occurs when the immune system mistakenly attacks the body's own cells, leading to autoimmune diseases (e.g., lupus, rheumatoid arthritis).

Immunodeficiency

  • Situations where the immune system's ability to fight infections is compromised, which can be genetic (like SCID) or acquired (like HIV).

Gut Microbiome

  • The gut microbiome plays a critical role in regulating the immune system and its responses; a healthy microbiome can enhance immune function.

Environmental Influences

  • Factors such as stress, diet, sleep, and physical activity can impact immune function, either strengthening or weakening the immune response.

  • Overall, understanding the immune system involves recognizing its complexity and the interplay of various factors that influence its effectiveness in protecting against diseases.