KS

Animal defence part 1

Immunology Concepts

Learning Outcomes

  • The discussion will cover concepts related to immunology and the immune system.

Immune System

  • The immune system defends the body against microorganisms.
  • Pathogen: Any microorganism that can cause harm or disease.
  • The immune system differentiates between self and non-self (harmful) microorganisms.

Phases of Immune Response

  1. Recognition Phase:
    • Discrimination between self and non-self.
  2. Activation Phase:
    • Immune cells mobilize and interact with the pathogen.
  3. Effector Phase:
    • Immune cells perform specific actions to remove the pathogen.

Types of Defenses

  1. Non-Specific Defense (Innate Immunity)
    • Acts quickly and is not specific to the pathogen.
    • First line of defense.
    • Recognizes a potential non-self pathogen and attempts to tackle it quickly.
  2. Specific Defense (Adaptive Immunity)
    • Highly specific to the pathogen.
    • Takes longer to activate but is long-lasting.
    • Innate immunity informs adaptive immunity to produce specific weapons (antibodies).
    • Adaptive immunity remembers the pathogen for future encounters.

Coordinated Immune System Components

  • Lymphoid Tissues:
    • Tissues involved in the production of immune cells.
    • Examples: Thymus, bone marrow, spleen, lymph nodes.
  • Blood Plasma:
    • Contains ions, small molecules, and proteins.
    • Contains red and white blood cells, and platelets.
  • White Blood Cells (Leukocytes):
    • Key cells of the immune system found in the blood and lymphatic system.
  • Lymphatic System:
    • A parallel system to the bloodstream for white blood cell circulation and maturation.
    • Composed mostly of lymphocytes.
  • Thoracic Duct:
    • The point of exchange between the circulatory and lymphatic systems.

Cell Generation

  • Red and white blood cells originate from multipotent stem cells in the bone marrow.
  • Multipotent Hematopoietic Cell Differentiation:
    • Differentiates into myeloid progenitor cells and lymphoid progenitor cells.
  • Myeloid Progenitor Cells
    • Generate red blood cells, platelets, and some white blood cells (leukocytes).
    • Can further differentiate into granulocytes: basophils, eosinophils, neutrophils, mast cells, macrophages, and dendritic cells.
    • Macrophages are phagocytic cells.
  • Lymphoid Progenitor Cells
    • Generate lymphocytes: B lymphocytes, T lymphocytes, and natural killer cells.

Cell Functions

  • Phagocytes:
    • Cells that engulf and digest pathogens.
    • Generally larger than lymphocytes.
  • Lymphocytes:
    • Do not perform phagocytosis.
    • Include B cells, T cells, and natural killer cells.
    • Produce antibodies (B lymphocytes).
    • Adaptive Cell's instructions to recognize pathogen are called antigens.

Antigen Presentation

  • Major Histocompatibility Complex (MHC):
    • Complexes on cell surfaces that present antigens to immune cells.
    • MHC Class I: Found on all nucleated cells.
      • Red blood cells are an exception as they do not have a nucleus and, therefore, lack MHC Class I.
    • MHC Class II: Primarily found on immune cells.
  • T Cells:
    • Lymphocytes with receptors that recognize antigens presented by MHC complexes.

Signaling Molecules (Cytokines)

  • Promote recruitment and activation of immune cells.

Non-Specific Defenses (Innate Immunity)

Physical and Chemical Barriers

  • Prevent pathogen invasion.
  • Skin: A major physical barrier.
  • Flora: Creates an unfavorable environment for exogenous pathogens.
  • Tears, Nasal Mucus, Saliva: Contain enzymes that destroy pathogens.
  • Mucus Membranes: Contain protective agents.

Complement System

  • A system that complements the action of the immune system.
  • Activated with innate immunity to target pathogens.
  • Forms pores on pathogen surfaces, causing lysis.

Interferons

  • Signaling molecules produced by infected cells.
  • Increase resistance to pathogens in surrounding cells.

Phagocytes (Macrophages)

  • Actively seek pathogens.
  • Recognize viruses, bacteria, and pathogen fragments.
  • Engulf and destroy pathogens.

Natural Killer Cells

  • Lymphocytes of the innate immunity.
  • Recognize and destroy virus-infected and tumor cells.

Inflammation Process

  • Indicates immune system activation.
  • Recruits immune cells to the site of infection.
  • Mast Cells: Release substances upon encountering pathogens, triggering an immune response.

Cytokines and Chemokines

  • Tumor Necrosis Factor: Kills target cells and activates immune system.
  • Prostaglandins: Weaken blood vessel membranes, allowing immune cell movement into tissues.
  • Histamine: Causes itching and allergic reactions.

Symptoms of Inflammation

  • Redness
  • Heat
  • Pain
  • Blood vessel dilation and increased permeability.
  • Activation of complement and involvement of phagocytic cells.

Macrophage Function

  • Engulf pathogens and produce cytokines.
  • Cytokines recruit other cells and signal the brain, causing fever.

Fever

  • Increases the rate of lymphocyte and phagocyte production and activity.
  • Creates an unfavorable environment for pathogen growth.

Over-Inflammation

  • May indicate immune system dysfunction.
  • Results from allergies or autoimmune diseases.
  • Sepsis: Uncontrolled inflammation spreading through the bloodstream.

Pathogen Recognition

  • Pathogens have specific molecules on their surface.
  • Leukocytes (e.g., macrophages) have Toll-Like Receptors (TLRs) that recognize these molecules.
  • TLRs are a family of receptors that recognize non-self structures.

Toll-Like Receptors (TLRs)

  • Recognize sugars, DNA fragments, and other structures on pathogens.
  • CD14 Protein: Produced by macrophages; binds to TLRs and enhances their activation.
  • TLR activation leads to signaling pathways involving NFKB transcriptional factor.
  • NFKB Transcriptional Factor: Activates genes involved in the macrophage response, such as digestion and cytokine release.

Adaptive Immunity

  • Triggered by pathogens or toxins.
  • Passive Immunization: Transferring antibodies from a person affected by a specfic pathogen. Provide temporary immunization.

Key Factors of Specific Immunity

  1. Specificity: Ability to produce specific weapons against pathogens.
  2. Self/Non-Self Discrimination: Ability to differentiate between self and non-self.
  3. Diversity: Ability to produce specific weapons for different pathogens.
  4. Immunological Memory: Ability to remember pathogens and quickly produce antibodies upon re-exposure.

Lymphocyte Specificity

  • Lymphocytes recognize specific information (antigens) from pathogens using receptors.
  • Antigen Presentation: MHC complexes present antigens to lymphocytes.

Antigen Types

  • Antigens are peptides (amino acid chains).
  • Length varies depending on the antigen and MHC complex.
  • Lymphocytes recognize antigens presented by MHC I or MHC II complexes.

Self vs. Non-Self Recognition

  • Lymphocytes are screened during production for their ability to recognize self antigens.
  • Tolerance: Lymphocytes do not interact with self antigens due to this screening process.
  • Lymphocytes attack non-self structures (pathogens) that are unusual to the body.

Diversity of Immune System

  • The immune system responds to different pathogens by activating specific lymphocytes.
  • The immune system can differentiate among billions of potential pathogens.

Immunological Memory

  • Upon encountering a pathogen, lymphocytes (B cells) remember it.
  • Upon re-exposure, specific antibodies are produced quickly.

Types of Immune Responses

  1. Humoral Immune Response:
    • Involves B cells and antibody production.
  2. Cellular Immune Response:
    • Involves cytotoxic T cells.
  • Both responses work simultaneously.
  • Key Event: Antigen presentation to T and B lymphocytes.
  • T Helper Lymphocytes: Instruct B cells to produce antibodies and stimulate T cytotoxic cells.

T Helper Cell Function

  • Stimulate T cytotoxic cells to recognize and destroy infected cells.
  • Stimulate B cells to produce antibodies.
  • Antibodies bind to antigens on infected cells or free antigens (e.g., toxins, pathogen fragments).

T Cell Activation

  • Infected cells present antigens through MHC complexes.
  • T cell receptors recognize the antigen and become activated.
  • Activated T cells proliferate and kill infected cells (cytotoxic T cells).

Receptor Diversity

  • Receptors on lymphocytes are diverse due to gene reorganization.
  • Two genes encode lymphocyte receptors (not one gene, one protein).

Antibody and Cell Generation

  • Antigen is recognized by receptors on B lymphocytes.
  • B lymphocytes clone themselves, creating more cells with the same receptor.
  • T helper cells instruct these cells to become plasma cells (releasing antibodies) or memory cells.

Primary vs. Secondary Immune Response

  • Primary Immune Response: Initial contact with antigen; lymphocyte proliferation and memory cell creation.
  • Secondary Immune Response: Re-exposure to the same antigen; memory cells proliferate into plasma cells, producing antibodies.

Active Immunity

  • Immune system develops a specific response through memory cells.
  • Provides long-lasting protection.

Vaccination

  • Instructs the immune system to produce antibodies.
  • Involves presenting an inactive or attenuated pathogen to the immune system.
  • Uses recombinant DNA technology.
  • Stimulates the immune system without causing disease.

Tolerance

  • Mechanism to prevent immune cells from recognizing self antigens.
  • Involves screening lymphocyte receptors during production.
  • Clonal Selection: Lymphocytes that recognize self antigens are eliminated.