IM 2

Innate Immunity

  • Definition of Innate Immunity
    • Innate immunity is the first line of defense in the immune system, reacting to pathogens and damage.

Inflammatory Response

  • Initiation of Inflammatory Response

    • Initiated when immune cells recognize pathogens or damaged cells.
    • Neutrophil Function
    • Neutrophils have surface receptors that can recognize pathogens.
    • Pathogen-Associated Molecular Patterns (PAMPs)
    • Definition: PAMPs are integral proteins on pathogen surfaces, recognized by the immune system.
    • Damage-Associated Molecular Patterns (DAMPs)
    • Definition: DAMPs are substances released from damaged cells.

  • Functions of Inflammatory Response

    • Reduces spread of pathogens.
    • Destroys invading pathogens with phagocytes (neutrophils, macrophages, dendritic cells, and natural killer cells).
    • Increases local blood flow.
    • Enhances clotting mechanisms (Details to be discussed in the cardiovascular system section).
    • Removes pathogens and damaged tissues through processes like phagocytosis by macrophages.
    • Participates in healing response post-tissue damage.

Mechanism of Innate Immune Response

  • Pathogen Entry

    • Pathogens breach the epithelial barrier of the skin, replicating and activating the complement system.

  • Complement System

    • Functions by creating membrane attack complexes or opsonization, enhancing phagocytosis.
    • Membrane Attack Complexes: Lyse bacteria, leading to their destruction.
    • Opsonization: Coating pathogens to enhance phagocyte recognition.

  • Phagocytosis Process

    • A macrophage phagocytoses, processes the pathogen, and releases cytotoxic molecules:
    • Cytokines and Chemokines:
      • Act as chemical messengers for local inflammatory response and recruitment of additional inflammatory cells.
    • Calls in additional leukocytes, including neutrophils and granulocytes, which themselves produce more cytokines to amplify the inflammatory response.

  • Response Duration

    • The innate immune response continues until the pathogen is completely eradicated.

Symptoms and Signs of Inflammation

  • Local Factors of Inflammation

    • Increases in blood flow and vascular permeability.
    • Increased metabolic activity leading to localized increased temperature.
    • Release of pyrogens that can induce fever.
    • Release of bradykinins that sensitize nerve receptors, contributing to pain.

  • Four Classic Signs of Inflammation

    • Rubor (Redness)
    • Result of increased blood flow in the affected area.
    • Calor (Heat)
    • Caused by increased metabolic activity.
    • Tumor (Swelling)
    • Due to increased blood flow and accumulation of interstitial fluid.
    • Dolor (Pain)
    • Resulting from nerve sensitization due to bradykinin release.

  • Real-World Examples of Inflammation

    • Conditions like boils and localized abscesses demonstrate signs of innate immune response.

Adaptive Immunity

  • Adaptive Immunity Overview
    • Activated if innate immune response fails to resolve an infection.
    • Characterized by a targeted, inducible response against specific pathogens.

Key Components of Adaptive Immune Response

  • Antigen Presenting Cells (APCs)

    • Include macrophages and dendritic cells.
    • Interact with naive lymphocytes (those unexposed to the pathogen).

  • B Lymphocytes

    • Have antigen receptors recognizing specific pathogens.
    • Upon interaction with a specific pathogen, they can transform into:
    • Plasma Cells
      • Produce specific antibodies against the recognized pathogen.
      • Antibodies circulate in plasma and facilitate infection combat in various ways:
      • Surround a pathogen, blocking its cell binding sites.
      • Perform opsonization to enhance phagocytosis.
      • Cause agglutination, clumping pathogens to prevent cell invasion.
    • Memory B Cells
      • Ensure rapid and enhanced antibody response upon future exposures to the same pathogen.

  • T Lymphocytes

    • Activated through interactions with naive T cells in the presence of antigen presented by APCs.
    • Can differentiate into:
    • Cytotoxic T Cells (T Killer Cells)
      • Destroy infected cells.
    • T Helper Cells
      • Activate macrophages to enhance their pathogen destruction ability.
      • Help activate B cells for further antibody production.
      • Recruit various granulocytes to enhance the immune response.
    • Memory T Cells
      • Facilitate rapid response to previously encountered pathogens and interact with macrophages, B cells, or dendritic cells to initiate quicker responses.

Immune Response Dynamics

  • Primary vs. Secondary Immune Responses

    • Primary Immune Response
    • Occurs upon first exposure to a pathogen with a gradual build-up of antibody levels over several days.
    • Typically takes about one week for antibodies to appear in sufficient quantity.
    • Secondary Immune Response
    • Triggered by subsequent exposures to the same pathogen, leading to a faster and more robust antibody response, typically occurring within three days.
    • Memory B cells and T cells enable this quick response.

  • Graphical Representation of Immune Responses

    • Y-axis: Antibody Levels
    • X-axis: Time
    • Characterizes antibody level increase and subsequent decreases over time following both primary and secondary exposures to pathogens.