Biology: Immune System

• Immune system


  Cells, tissues, and molecules that mediate resistance to infections
• Immunology


  Study of structure and function of immune system
• Immunity


  Resistance of a host to pathogens and their toxic effects
• Immune response


  Collective and coordinated response to the introduction of foreign substances in an individual mediated by the cells and molecules of the immune system
• Role of the immune system

  • Defense against microbes
  • Defense against the growth of tumor cells
  • Kills the growth of tumor cells
  • Homeostasis
  • Destruction of abnormal or dead cells (e.g. dead red or white blood cells, antigen-antibody complex)
• Immune system organs

  • Tonsils and adenoids
  • Thymus
  • Lymph nodes
  • Spleen
  • Payer's patches
  • Appendix
  • Lymphatic vessels
  • Bone marrow
• Immune system cells


  • Lymphocytes (White Blood Cells)
  • T-lymphocytes
  • B-Lymphocytes, plasma cells
  • Natural killer lymphocytes
  • Monocytes, Macrophage
• Immune system molecules

  • Antibodies
• Types of immunity

  • Innate (non-adaptive)
  • Acquired (adaptive)
• Innate immunity

  • First line of immune response
  • Relies on mechanisms that exist before infection
  • Rapid response: within minutes of infection
  • Not specific
  • Has no memory - same response after repeated exposure
• Innate immunity mechanisms

  • Mechanical barriers / surface secretion (skin, acidic pH in stomach, mucus)
  • Cellular defense mechanisms
• Adaptive (Acquired) immunity


  • Second line of response (if innate fails)
  • Relies on mechanisms that adapt after infection
  • Handled by T- and B- lymphocytes
  • One cell determines one antigenic determinant
  • Based upon resistance acquired during life
  • Responds more slowly, over few days
  • Is specific
  • Has memory - repeated exposure leads to faster, stronger response
• Adaptive immunity types

  • Active
  • Passive
• Active immunity


  • Natural (clinical, sub-clinical infection)
  • Artificial (Vaccination: Live, killed, purified antigen)
• Passive immunity


  • Natural (via breast milk, placenta)
  • Artificial (immune serum, immune cells)
• Adaptive immunity mechanisms

  • Cell-mediated immune response (CMIR) (T-lymphocytes - recognizes antigen, eliminate intracellular microbes that survive within phagocytes or other infected cells)
  • Humoral immune response (HIR) (B-lymphocytes - recognize specific antigens, produces antibodies, eliminate extra-cellular microbes and their toxins)
• Failures of immune response

  • Hypersensitivity reactions
  • Immunodeficiency
• Hypersensitivity

  Overreaction to infectious agents
• Allergy

  Overreaction to environmental substances
• Autoimmunity

  Overreaction to self
• Immunodeficiency types


  • Congenital (primary) (genetic abnormality)
  • Acquired (secondary) (results from infections, nutritional deficiencies or treatments (AIDS, chronic leukemia))