DN

Microbiology Unit VI & Chapter 18 & 19 Notes

Adaptive Specific Host Defenses

  • Adaptive immunity attributes:
    • Specificity: targets specific antigens.
    • Memory: remembers past encounters for a stronger response upon re-exposure.
    • Clonality: generates clones of lymphocytes specific to an antigen.
    • Self-recognition: ability to distinguish between self and non-self.
  • Humoral vs. Cellular Immunity:
    • Humoral: Involves antibodies produced by B cells that target extracellular pathogens.
    • Cellular: Involves T cells that target intracellular pathogens or abnormal cells.
  • Definitions:
    • Antigen: A substance that triggers an immune response.
    • Epitope: The specific part of an antigen that an antibody or T cell receptor binds to.
    • Hapten: A small molecule that can elicit an immune response only when attached to a carrier protein.
  • Good Antigen Characteristics:
    • High molecular weight.
    • Structural complexity.
    • Foreignness.
    • Accessibility.
  • Antibody Structure:
    • Composed of two heavy chains and two light chains.
    • Variable regions at the tips of the chains determine specificity.
    • Constant regions determine the antibody class.
  • Immunoglobulin Classes:
    • IgG: Most abundant, crosses the placenta, provides long-term immunity.
    • IgM: First antibody produced during an infection, good at complement activation.
    • IgA: Found in mucosal secretions, provides localized immunity.
    • IgE: Involved in allergic reactions and parasitic infections.
    • IgD: Function not fully understood, found on B cells.
  • Antibody Functions:
    • Opsonization: Enhances phagocytosis.
    • Neutralization: Blocks pathogens from infecting cells.
    • Complement activation: Triggers the complement cascade to destroy pathogens.
    • Agglutination: Clumps pathogens together for easier clearance.
    • Antibody-dependent cell-mediated cytotoxicity (ADCC): Targets infected cells for destruction by natural killer cells.
  • MHC Role in Immunity:
    • MHC molecules present antigens to T cells.
    • MHC I: Found on all nucleated cells, presents intracellular antigens to cytotoxic T cells.
    • MHC II: Found on antigen-presenting cells (APCs), presents extracellular antigens to helper T cells.
  • Antigen Presenting Cells (APCs):
    • APCs engulf and process antigens, then present them to T cells.
    • Examples: dendritic cells, macrophages, B cells.
  • Lymphocyte Development & Function:
    • B cells develop in the bone marrow and produce antibodies.
    • T cells develop in the thymus and mediate cellular immunity.
    • Both undergo selection processes to ensure self-tolerance.
  • Central Tolerance/Self-Tolerance:
    • Elimination of self-reactive lymphocytes during development to prevent autoimmunity.
  • T Lymphocyte Types:
    • Cytotoxic T cells: Kill infected or abnormal cells.
    • Helper T cells: Activate B cells and other immune cells.
    • Regulatory T cells: Suppress the immune response to prevent excessive inflammation and autoimmunity.
  • Cluster of Differentiation (CD) Molecules:
    • Surface proteins on immune cells that help distinguish cell types and mediate interactions.
  • Roles in Specific Immunity:
    • Plasma cells: Produce antibodies.
    • Memory cells: Provide long-term immunity.
    • Helper T cells: Coordinate immune responses.
    • Cytotoxic T cells: Kill infected cells.
    • Regulatory T cells: suppress immune responses.
    • Antigen presenting cells: Present antigens to T cells.
    • Perforin: creates pores in target cell membranes.
    • Granzymes: induce apoptosis in target cells.
    • Natural killer cells: kill infected or cancerous cells.
    • MHC I and II molecules: present antigens to T cells
    • TCR’s: T cell receptors on T cells.
    • BCR’s: B cell receptors on B cells.
  • Naïve vs. Effector vs. Memory Cells:
    • Naïve cells: Have not yet encountered their specific antigen.
    • Effector cells: Actively involved in an immune response.
    • Memory cells: Long-lived cells that provide immunological memory.
  • TH1 vs. TH2 Cells:
    • T_H1: Activate macrophages and cytotoxic T cells, promote cell-mediated immunity.
    • T_H2: Activate B cells and promote humoral immunity.
  • T-Cell Independent vs. Dependent Activation of B Cells:
    • T-cell independent: B cell activation without T cell help, usually involves repetitive antigens.
    • T-cell dependent: B cell activation requires T cell help, results in stronger and longer-lasting immunity.
  • Primary vs. Secondary Antibody Response:
    • Primary: Slower and weaker response upon initial exposure to an antigen.
    • Secondary: Faster and stronger response upon subsequent exposure due to memory cells.
  • States of Immunity:
    • Active: Immunity acquired through exposure to an antigen, either naturally or artificially (vaccination).
      • Example: Infection (natural), vaccination (artificial).
    • Passive: Immunity acquired through transfer of antibodies, either naturally or artificially (antibody injection).
      • Example: Maternal antibodies (natural), antibody injection (artificial).
    • Natural: Acquired through natural processes, such as infection or maternal antibodies.
    • Artificial: Acquired through medical intervention, such as vaccination or antibody injection.
  • Herd Immunity:
    • Protection of a population from infection due to a high percentage of individuals being immune.
  • Antigen Preparations for Vaccines:
    • Live attenuated vaccines.
    • Inactivated vaccines.
    • Subunit vaccines.
    • Toxoid vaccines.
    • Conjugate vaccines.

Diseases of the Immune System

  • Hypersensitivity Reactions:
    • Malfunction of the immune system leading to excessive or inappropriate immune responses.
  • Types of Hypersensitivity Reactions:
    • Type I (Immediate): IgE-mediated, involves mast cell degranulation and histamine release.
      • Example: Allergies.
    • Type II (Cytotoxic): Antibody-mediated destruction of cells.
      • Example: Blood transfusion reactions.
    • Type III (Immune Complex): Immune complex deposition leading to inflammation.
      • Example: Serum sickness.
    • Type IV (Delayed-Type): T cell-mediated, delayed response.
      • Example: Contact dermatitis.
  • ABO Blood Group System and Rh Factor:
    • Importance in blood transfusions and pregnancies to prevent immune reactions.
    • ABO: Antibodies against A or B antigens.
    • Rh: Antibodies against Rh factor (D antigen).
  • Sensitization:
    • Initial exposure to an antigen that leads to an immune response upon subsequent exposure.
  • Histamine:
    • Role in allergic responses, causes vasodilation, increased vascular permeability, and bronchoconstriction.
  • Allergen:
    • A substance that causes an allergic reaction.
    • Categories: Inhalants, foods, injectables, contactants.
  • Hypersensitivity Diagnosis:
    • Skin prick tests.
    • Blood tests.
  • Hypersensitivity Treatment:
    • Avoidance.
    • Antihistamines.
    • Corticosteroids.
    • Epinephrine.
    • Immunotherapy.
  • Autoimmune Disease:
    • Malfunction of the immune system leading to attack on self-antigens.
  • Organ-Specific vs. Systemic Autoimmune Disease:
    • Organ-specific: targets a single organ.
      • Example: Type 1 diabetes.
    • Systemic: affects multiple organs.
      • Example: Lupus.
  • Immune System in Organ Transplantation and Rejection:
    • Immune system recognizes transplanted organs as foreign and attacks them.
    • Prevention: Immunosuppressant drugs.
  • Immunodeficiency:
    • Malfunction of the immune system leading to increased susceptibility to infection.
  • Primary vs. Secondary Immunodeficiency:
    • Primary: Genetic defects.
      • Example: SCID.
    • Secondary: Acquired due to infection, malnutrition, or other factors.
      • Example: AIDS.