The immune system

• Immune system

  The body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells
• Immunity


  The body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells
• Pathogen


  Infectious agents that cause damage
• Types of pathogens


  • Fungi
  • Protocista
  • Multicellular parasites
  • Viruses
  • Bacteria
• Virulence


  The disease producing power of a pathogen
• Antigen


  Molecules from a pathogen or foreign organism that provoke a specific immune response

  
• Immune system responses vary and depend on the pathogen

  
• Cells


  Cyte- cell, Leuko-white, Macro-big, Phago-eat, Poly-many, Morph-change shape
• Molecules/soluble factors


  Antibodies, Cytokines, Complement, Inflammatory mediators i.e. Histamine
• Immune system is the protection and repair mechanism of our body

  
• Exterior defences


  • Non-specific defence mechanisms
• Exterior defences


  1. The skin and mucous lining block entry of viruses and bacteria

  2. Cells of the mucous membrane produce mucus - traps microbes

  3. Mucous secretions, saliva, tears, and cilia: washing actions - bar microbes

  4. Acidity of the stomach destroys microbes in food and water

  5. Lysozymes digest the cell wall of bacteria

  6. Tissue fluids contain antimicrobial agents
• Hematopoietic stem cells


  Cells that most immune cells derive from
• Immune cells


  • Neutrophil
  • Eosinophil
  • Basophil
  • Lymphocyte
  • Monocyte
  • Platelet

  
• CD markers and receptors


  Characteristic surface molecules that identify immune cell types

  
• Soluble mediators


  Cytokines, Chemokines, Antibodies, Complement, Other inflammatory mediators: Histamine, PG etc

  
• Cytokines


  Immunomodulating agents- signalling molecules in cellular communication
• Leukocytes (WBCs)


  The only blood components that are complete cells, protect the body from infectious microorganisms

  
• Types of leukocytes


  • Granulocytes: Neutrophils, Eosinophils, Basophils
  • Agranulocytes: Monocytes, Lymphocytes

  
• Leukocytosis


  WBC count over 11,000/mm3, normal response to bacterial or viral invasion

  
• Leukopenia


  A decrease in WBC count below 4,800/mm3
• Leukemia


  A cancer of WBC
• Granulocytes


  • Contain cytoplasmic granules that stain specifically, have lobed nuclei, are all phagocytic cells

  
• Neutrophils


  The most numerous of the leukocytes in blood (60% of WBCs), functions include phagocytosis of bacteria and release of antimicrobial chemicals

  
• Neutrophils


  • Patrol tissues as they squeeze out of the capillaries, constitute a defense against invasion by microorganisms, especially bacteria, granules are lysosomes

  
• Basophils


  The least numerous of the leukocytes in blood (0.5-1% of all WBCs), granules contain heparin and histamine and capable of generating leukotrienes, functions include secreting histamine and heparin

  
• Eosinophils


  They account for 1–4% of WBCs, granules contain major basic protein and a variety of hydrolytic enzymes, functions include phagocytosis of antigen-antibody complexes, allergens, and release of enzymes to weaken or destroy parasites such as worms
• Monocytes


  They account for 3–7% of leukocytes, the largest white cells (14~20 μm)

  
• Macrophages


  Tissue associated (found in the organs, not the blood), made in bone marrow as monocytes, long lived, mostly associated with chronic inflammation, functions include phagocytosis of bacteria and initiation of immune responses by displaying antigens to lymphocytes

  
• Dendritic cells (DCs)


  Professional antigen-presenting cells, have processes called dendrites, present in tissues in contact with the external environment where they sample their environment, function is to initiate adaptive immune responses by detecting and capturing intruders, processing antigen material and presenting it to T cells
• Lymphocytes


  Account for 20-25% or more of WBCs, have large, dark-purple, circular nuclei with a thin rim of blue cytoplasm, functions include initiating the adaptive response, producing antibodies, recognising foreign molecules, killing/attacking infected cells, secretion of signalling molecules, and regulation of both innate and adaptive immune cells

  
• Types of lymphocytes


  • T cells
  • B cells
  • NK cells
  • Innate Lymphoid cells

  
• 1. Lymphocytes


  Mature in the thymus and then circulate in the blood and lymph, have T cell receptors (TCR) that recognize and react to a specific antigen combined with MHC proteins, can form T-helper cells, cytotoxic T cells, and memory T cells after activation

  
• 1. Lymphocytes


  Mature in bone marrow then concentrate in lymph nodes and spleen, and circulate in the blood and lymph, produce antibodies, have 10 million different B-lymphocytes each making a different antibody, have antibody receptors or B cell receptors (BCR) embedded in the plasma membrane

  
• Natural Killer (NK) cells

  Larger lymphocytes capable of recognizing cells that do not express "self" proteins or contain foreign/abnormal markers, release cytotoxic granules containing perforin and granzymes to lyse target cells

  
• Innate Lymphoid Cells (ILCs)

  Most recently discovered family of innate immune cells, lymphocytes that do not express antigen receptors like T cells and B cells, primarily tissue resident cells particularly abundant at mucosal surfaces, act as "first responders"

  
• ILC Subsets


  • ILC1
  • ILC2
  • ILC3
  • NK cells
  • LTi cells
• Innate immune system


  First line of defence, involves non-specific generalised responses including Complement & phagocytosis

  
• Adaptive immune system


  Adapts as the pathogens adapt, involves T cells, B cells and antibodies

  
• Innate immune responses are the SAME on each encounter with the antigen