IMMUNE SYSTEMS

• Immune system


  A complex network of different cellular actions and signals, allowing an organism to defend itself against a pathogen
• Immune system


  • It transmits information by chemical signals, or through the migration of cells
  • It recognizes and protects the organism against pathogens, whereby foreign structures and molecules get recognized and an appropriate immune response is produced
• Autoimmune diseases


  Condition arising from an abnormal immune response to a functioning body part
• Immunodeficiency


  When the immune system is less active than normal, resulting in recurring and life-threatening infections
• Immunology


  A branch of biology that covers the study of immune systems in all organisms
• Innate immune system


  Inherited, nonspecific defense mechanisms that come into play immediately after a pathogen is recognized
• Adaptive immune system


  Antigen-specific immune responses, more complex than the innate one, includes a "memory process"
• Plant immune system


  • Plants are protected from infection by a "skin," a waxy cuticular layer atop the cell wall
  • Consequent regulation of a network of inducible defenses can halt pathogen proliferation and signal distal plant organs to become nonspecifically primed against further infection
• Plant-pathogen interaction


  1. PRR (Pattern Recognition Receptor) on plant cell surface recognizes PAMP/MAMP (Pathogen Associated Molecular Pattern or Microbe Associated Molecular Pattern) on pathogen, triggering PTI (Pattern/PAMP Triggered Immunity)

  2. R-Gene (Resistance protein) is activated when pathogen effector molecules get inside the cell, triggering ETI (Effector Triggered Immunity)
• Systemic Acquired Response (SAR)

  Broad-ranging resistance that lasts for a period of days, triggered by signals like salicylic acid and jasmonic acid
• Lines of defense in animal immunity

  • Surface barriers that prevent entry of pathogens
  • Non-specific phagocytes and other internal mechanisms of innate immunity
  • Specific lymphocytes that produce antibodies of adaptive immunity
• Salicylic acid


  The active ingredient in aspirin
• SAR (systemic acquired resistance)


  Allows the plant to respond more quickly if it is attacked again
• SAR is not the same as the human immune response where antibodies (proteins) that recognize specific antigens (foreign proteins) persist in the body
• SAR is neither as specific nor long lasting as the human immune response
• Gene-for-gene response in plant defense

  1. Cascade of events triggered

  2. Leads to local cell death (HR response)

  3. Leads to longer-term resistance in the rest of the plant (SAR)
• Three basic lines of defense in the animal immune system

  • Surface barriers that prevent the entry of pathogens
  • Non-specific phagocytes and other internal mechanisms that comprise innate immunity
  • Specific lymphocytes that produce antibodies as part of the adaptive immune response
• Antigens


  Proteins on the surface of invading bacteria or on virus-infected cells
• Self-antigens


  Antigens unique to an individual's own cells
• Nonself-antigens


  Antigens on invading germs that do not originate in the body
• The immune system is designed to identify cells with nonself-antigens as harmful and respond appropriately
• Most immune cells release cytokines (messengers) to help them communicate with other immune cells and control the response to any threats
• Immune response to a normal invader

  1. Immune cells in the injured tissue respond and call other immune cells to gather at the site

  2. Immune cells release cytokines to call other immune cells to help defend the body

  3. Natural killer cells begin to destroy the invaders with a general attack

  4. Dendritic cells engulf the invaders and their nonself-antigens, mature into antigen-presenting cells (APCs)

  5. APCs expose the invading cells to B and T cells so they can recognize the invaders

  6. B cells produce antibodies to help identify and stop the invading bacteria

  7. T cells are designed to find abnormal fragments of viruses inside normal cells

  8. APCs communicate with and activate the naïve T cells by connecting to them through protein molecules on their surfaces

  9. T cell must receive both Signal 1 (MHC-antigen connection) and Signal 2 (co-stimulatory signal) to be fully activated

  10. Fully activated effector T cells multiply to expand the number of T cells equipped to defeat the threat

  11. Some T cells transform into regulatory T cells to slow and shut down the immune response once the threat is gone

  12. Some T cells become memory T cells that can stay alive for months or years to fight off the same invading cells again
• Memory is the basis of immune protection against disease in general and explains why we don't become infected with some diseases, such as measles or chicken pox, more than once