102 Innate (Non-specific) Immunity and Developing 4 Types of Adaptive (Specific) Immunity

Two Types of Immunity

It is often said that humans are protected by two types of immunity: innate and adaptive immunity.  Innate immunity provides non-specific protection against pathogens and other harmful environmental agents.  The term innate immunity is derived from the Latin word in which means into, and natus which means be born, so together meaning ‘to be born with’.  Adaptive immunity is categorized as the immune response that develops in response to a specific non-self antigen most often belonging to a harmful pathogen.

Innate (Non-specific) Immunity: This type of immunity is genetically determined and includes several physical and chemical barriers.  The physical barriers are the skin, which acts as a suit of armor; hair, which provides a physical barrier; and mucus and cerumen, which are sticky substances that trap pathogens. Mechanical barriers include cilia, peristalsis, and the rapid flow of urine through the urethra.  Chemical barriers involve the low pH of the stomach, the antimicrobial properties of bile, lysozymes and IgA antibodies in tears and saliva, and antimicrobial dermcidin in sebum and sweat.

The components of innate immunity are diverse.  Natural killer cells (NK cells) kill foreign and cancerous cells using perforin and granulysin, which create portals in targeted cells, causing water to leak in, and the cell to swell and burst due to osmotic lysis, a process called cytolysis.  Powerful phagocytes, such as neutrophils, fixed and free macrophages, monocytes, dendritic cells, microglia, and eosinophils, phagocytose pathogens, infected cells, and debris.  The complement system involves complement proteins that help destroy pathogens by creating membrane attack complexes (MACs), working as opsonins to assist phagocytes, and inducing mast cell and basophil degranulation.  Neutrophil toxins, such as reactive oxygen species (ROS), provide defense against bacteria, while eosinophil toxins target helminths (parasitic worms).  Inflammation, in response to infection or tissue damage, is stimulated by the release of pro-inflammatory cytokines like histamine and prostaglandin from mast cells and basophils, facilitating white blood cell (WBC) activity and healing.  Pyrogens cause fever, aiding the immune response by speeding up WBC activity and slowing down microbial growth.  Cytokines, including interferons, lymphokines, interleukins, and chemokines, act as chemical messages that allow WBCs to coordinate their defense.

Adaptive (Specific) Immunity:  This type of immunity is triggered by specific non-self antigens on pathogens and involves the activation of T and B lymphocytes and the production of antibodies.  The development of specific immunity occurs in one of four ways:

1. Naturally Acquired Active Immunity:  This occurs through exposure to a real pathogen or antigen. The individual may or may not show signs of infection, depending on the severity of the infection and the body’s ability to clear it. Active immunity involves the activation of T and B lymphocytes and the production of memory T and B cells.
2. Artificially Induced Active Immunity:  This is achieved through vaccination, where an administered antigen or a weakened or killed pathogen triggers the activation of T and B lymphocytes and the production of memory T and B cells.
3. Naturally Acquired Passive Immunity:  This involves the transfer of antibodies from mother to baby through the placenta or breastfeeding.
4. Artificially Induced Passive Immunity:  This is the medical administration of antibodies, such as in the treatment of Ebola virus or rabies virus, where plasma containing antibodies from survivors is donated and used to treat individuals that are infected.

Note that passive immunity is shorter-lived that active immunity, as memory T and B cells are not created.  Passive immunity lasts only as long as the introduced antibodies are active.  Antibodies, are recycled as are other proteins in the body.  The half-life of human IgG antibodies is approximately 3 weeks.  That being said, newly developed therapeutic antibodies are being designed to last longer (months instead of weeks).

Summary:

• Two Types of Immunity:
  • Adaptive/Specific Immunity
  • Innate/Non-specific Immunity

Innate/Non-specific Immunity:

• • Genetically determined
  • Includes physical barriers:
    • Skin (suit of armor)
    • Hair (physical barrier)
    • Mucus and cerumen (sticky, traps pathogens)
  • Mechanical barriers (cilia, peristalsis, rapid flow of urine through the urethra)
  • Chemical barriers (low pH of stomach, anti-microbial properties of bile, lysozymes and IgA antibodies in tears and saliva, antimicobial dermicidin in sebum and sweat)
  • Components:
    • Natural killer cells (kill foreign cells and cancerous cells) using perforin and granulysin to create portals in targeted cells, water leaks in, cell swells and bursts due to osmotic lysis (cytolysis)
    • Powerful phagocytes (e.g., neutrophils, fixed and free macrophages, monocytes, dendritic cells, microglia, eosinophils) that phagocytose pathogens, infected cells and debris.
    • Complement system – complement proteins that help to destroy pathogens by create MACs (membrane attack complexes), work as opsonins to assist phagocytes, and induce mast cell and basophil degranulation
    • Neturophil toxins (e.g., ROS) that provide defense against bacteria
    • Eosinophil toxins that provide defense against helminths (parastic worms)
    • Inflammation (in response to infection or tissue damage) stimulated by pro-inflammatory cytokines (e.g., histamine, prostaglandin) release or degranulation from mast cells and basophils
    • Inflammation facilitates WBC activity and healing
    • Pyrogens (cause fever, aiding immune response as increased temperature speeds up WBC activity and can slow down microbial growth)
    • Cytokines (e.g., Interferons, Lymphokines, Interleukins, Chemokines) – chemical messeages that allow WBCs to coordinate defense

Adaptive/Specific Immunity:

• • Triggered by specific non-self antigens on pathogens
  • Involves activation of T and B lymphocytes and production of antibodies
• Development of Specific Immunity occurs in one of four ways:
  • Active Immunity:
    • 1. Naturally Acquired Active Immunity:
      • Exposure to real pathogen/antigen -may or may not show signs of infections (asymptomatic or symptomatic) depending on the severity of the infection and ability of the body to clear the infection
      • Active immunity invovles the activation of T and B lymphocytes and production of memory T and B cells
    • 2. Artificially Induced Active Immunity:
      • Vaccination (administered antigen, weakened or killed pathogen)Active immunity invovles the activation of T and B lymphocytes and production of memory T and B cells
  • Passive Immunity:
    • 3. Naturally Acquired Passive Immunity:
      • Transfer of antibodies from mother to baby (placenta, breastfeeding)
    • 4. Artificially Induced Passive Immunity:
      • Medical administration of antibodies (e.g., Ebola virus, rabies)
      • Plasma containing antibodies from survivors is used to treat others