Bio AOS1 U4

• Antigens


  Molecules that elicit an immune response

  
• Antigens


  • Play crucial role in immunity
  • Can be recognised by T lymphocytes or by antibodies produced by B lymphocytes
  • Importance = recognise potentially harmful pathogens and mount an immune response against them

  
• Antibodies and antigens


  Work as a lock and key
• Structure of antigens


  • Protein-based (composed of one/more polypeptide chains)
  • Carbohydrates
  • Lipids
  • Nucleic acids
• Types of antigens


  • Self-antigens (present on the surface of your own cells, e.g. red blood cells)
  • Non self-antigens (foreign, e.g. bacteria)

  
• Allergens


  Antigens that cause allergic reactions
• Allergens


  Provoke hypersensitivity to a harmful substance
• Responding to antigens


  • B lymphocyte recognition (membrane-bound antibodies, secreted antibodies)
  • T lymphocyte recognition (receptors on T lymphocytes, no secreted antibodies)

  
• Self-tolerance


  Inability to respond to self-antigens
• Autoimmune diseases


  Absence of self-tolerance
• MHC markers


  • MHC-I (present on all nucleated cells, presents antigens from virus infected cells, cancer cells, cytotoxic T cells)
  • MHC-II (only found in certain immune cells, presents antigens from phagocytosed and foreign cells)

  
• Pathogens


  Agents that cause disease
• Types of pathogens


  • Primary pathogens (can cause disease at any time)
  • Opportunistic pathogens (only cause disease on weakened host defence)
• Cellular pathogens


  • Extracellular (does not require a host cell to reproduce)
  • Intracellular (requires host cell to reproduce)
• Bacterial pathogens


  Some can live and reproduce only on the external surfaces of human cells or in body fluids, others can live and reproduce either inside or outside the cells of their host, some can only survive and reproduce within host cells

  
• Bacterial toxins


  • Exotoxins (secreted toxins)
  • Endotoxins (parts of outer membrane that are released when cell dies)
• Fungi


  • Unicellular eukaryotic cell
  • Reproduce by budding
  • Spreads by releasing spores
  • Invade the host with thread-like hyphae
  • Secrete digestive enzymes that break down host tissues and then absorb them
• Types of fungal infections

  • Subcutaneous (direct implantation of spores into skin via a puncture wound)
  • Cutaneous (fungi break down keratin protein in hair, skin, nails)
  • Systemic (occurs inside the body, usually starting from lungs)
• Viruses


  • Nucleic acid core (RNA or DNA)
  • Capsid (protein coat)
  • Envelope (lipid bilayer)
  • Unable to function outside of host cell
  • Antibiotic treatment is ineffective against virus
• Replication of viruses

  1. Virus attaches to specific host cell

  2. Virus injects nucleic acid material into host cell

  3. Uses host organelles and energy to transcribe more viral genes -> destroying host cell

  4. Viral particles bud off the cell and infect other cells
• viruses

  • Contains RNA instead of DNA
  • Contain enzyme reverse transcriptase (RNA TO DNA)
• Prions


  • Composed of only protein (abnormal folding to make infectious)
  • Seeks and Converts normal proteins into prions
  • Causes brain disease through making nerve cells burst
• Transmission of prions


  • Infection -> consumption of infected meat, exposed to contaminated surgical instruments
  • Hereditary -> autosomal dominant trait
• Adaptative immune response is unable to identify and respond to prions due to their similar normal proteins
• Differences between bacteria and viruses

  • Bacteria are cellular pathogens with cell membrane and ribosomes, viruses are non-cellular pathogens with protein coat and DNA/RNA
• Innate (non-specific) immunity


  Individuals are born with it, same response to every pathogen, no immunological memory, quicker

  
• Adaptive (specific) immunity


  Antigen-specific immune response, different response for each pathogen, immunological memory is acquired, takes longer

  
• Cell-mediated and humoral responses

  • Cell-mediated immunity (immune response mediated by immune cells, kill)
  • Humoral immunity (immune response mediated by soluble molecules, disable)

  
• Cells of the immune system


  • All are white blood cells, derived from stem cells in the bone marrow, include B lymphocytes and T lymphocytes

  
• Lines of defence


  • First line (non-specific, physical, chemical and microbiological barriers)
  • Second line (non-specific, immune cells and soluble proteins, inflammation)
  • Third line (specific, actions of T cells and B cells, antibodies)
• First line of defence

  • Non-specific, defence against pathogens, provide barriers of the innate immune system, physical, chemical and microbiological barriers, e.g. intact skin and mucous membrane

  
• Second line of defence

  • Non-specific, provided by immune cells and soluble proteins of the innate immune system, attack pathogens that do gain entry to the body, inflammation

  
• Third line of defence

  • Specific, provided by the immune cells of the adaptive immune system, various actions of T cells and B cells, antibodies tailored specifically to attack each invading pathogen

  
• Chemical barriers in animals


  Secretion of substances (chemicals or enzymes) that are present to kill pathogens
• Chemical barriers in animals

  • Secreted fatty and lactic acids contain lysosomes that break down pathogens
  • Secreted stomach acid and digestive enzymes kill pathogens during digestion
  • Fluids containing surfactant that coat pathogens to make it easier for macrophages to kill
• Chemical barriers in plants


  Secretion of substances (chemicals or enzymes) that are present to kill pathogens
• Chemical barriers in plants

  • Saponin in wheat disrupt cell membranes of fungi
  • Caffeine in coffee, tea, cocoa plants is toxic to insects and fungi
  • Tannins in tea and grapes are toxic to insects
  • Citronella in lemongrass repels insects
  • Defensins in barley and wheat are toxic to microbes
  • Chitinases in barley, tomato, banana disrupt cell membranes of fungi
• Microbacterial barriers in animals

  Presence of flora (non-pathogenic bacteria) create a physical barrier against pathogens
• Microbacterial barriers in animals

  • Flora is found on skin, mouth, nose, throat, gastrointestinal tract
  • Prevents growth and colonisation of other bacteria
  • Flora outcompetes pathogen for resources and space
  • Flora produces chemicals that reduce pH of microenvironment

  
• Innate immune response


  Non-specific, rapid, present in all animals, fixed responses, do not lead to immunological memory