immunology

• Immune system


  A remarkable network of organs, cells, and proteins that work together to protect our bodies from harmful invaders
• Innate Immune System


  • First line of defense
  • Provides generalized protection against a wide range of pathogens without prior exposure
  • Components include: physical barriers, phagocytes, natural killer cells, complement system, inflammation
• Innate system


  Acts swiftly but lacks specificity
• Acquired Immune System


  • More sophisticated and specific
  • Adapts to recognize and respond to specific pathogens
  • Components include: B cells, T cells, antigens, memory cells
• Adaptive system


  Takes longer to activate but provides long-lasting immunity
• Self vs. Non-Self Recognition


  • Immune system distinguishes between self molecules (our own cells) and non-self molecules (pathogens)
  • Failure to recognize self can lead to autoimmune diseases
  • Major Histocompatibility Complex (MHC) molecules play a crucial role in this recognition
• Lymphatic System


  • Includes lymph nodes, spleen, tonsils, and thymus
  • Lymph nodes filter lymph and trap pathogens
  • Spleen removes old red blood cells and detects infections
  • Thymus matures T cells
• Neuroimmune System


  • Represents the connection between the nervous and immune systems
  • Neurons release neurotransmitters that influence immune responses
  • Stress, emotions, and circadian rhythms impact immune function
  • Includes hormonal signals and cytokines that participate in signaling between the immune and nervous systems
  • Key cellular components are glial cells, including astrocytes, microglia, and oligodendrocytes
• Specific Immune Response (Adaptive Immunity)

  • Highly specific for individual microbial pathogens
  • Antigens are molecules found on the surface of pathogens and are unique to each pathogen
  • Lymphocytes (B cells and T cells) play a crucial role
  • B cells produce specific antibodies to a particular pathogen
  • T cells assist B cells (helper T cells) and directly kill infected cells (killer T cells)
  • Humoral Immunity is mediated by B cells producing specific antibodies
  • Cell-Mediated Immunity involves cytotoxic T cells that induce the lysis of infected cells
• Chemical Defenses


  • Inflammatory response: increases blood flow, blood vessels expand, and white blood cells invade to engulf and destroy bacteria
  • Fever: immune system may raise body temperature to slow or stop pathogen growth and speed up the immune response
• Triggers of innate immune response

  • PAMPs (pathogen-associated molecular patterns)
  • DAMPs (danger-associated molecular patterns)
  • Pattern-recognition receptors: Toll-like receptors, NOD-like receptors, RIG-I-like receptors, Absent in Melanoma 2
• Antigen


  Molecules that react with antibodies or T cells
• Immunogen


  Antigens that can initiate an immune response
• Antibody


  Immunoglobulin molecule in the blood and body fluids which binds specifically to an antigen
• Classes of Immunoglobulins


  • IgA
  • IgD
  • IgE
  • IgG
  • IgM
• Normal function of the immune system

  • To identify and eliminate harmful microorganisms and harmful substances
  • By distinguishing 'self' from 'non-self' proteins
  • By identifying 'danger' signals (e.g. from inflammation)
  • The immune system must strike a balance between clearing the pathogen and causing collateral damage to the host - "immunopathology"
• How the immune system can cause disease

  • Immune deficiency - persistent or fatal infections
  • Allergy
  • Autoimmune disease
  • Transplant rejection
• How an antibody kills a virus

  1. Binds to virus and prevents attachment to cell

  2. Opsonization: virus-Ab complex is phagocytosed by macrophages

  3. Complement-mediated lysis of enveloped viruses

  4. Antibody-dependent cell-mediated cytotoxicity (ADCC), mediated by natural killer (NK)-like cells
• How the immune response clears a pathogen

  1. Cytotoxic T lymphocytes (CTLs) kill infected cells

  2. Antibodies bind to pathogens: the complex is destroyed or ingested by cells
• How a T cell meets its antigen


  Antigens are taken up by specialized antigen-presenting cells and transported from the tissues into secondary lymphoid organs, where they meet T cells
• What happens when the antigen is removed

  • Most lymphocytes that have proliferated recently will die after fulfilling their function
  • Some survive as memory cells
• Vaccines


  Provide acquired immunity by exposing the immune system to harmless forms of pathogens, allowing it to develop specific defenses
• Nonspecific defenses act as the first line of protection, while specific immune responses are the third line of defense and are triggered by antigens