imune

• Responding to antigens

  Physical, chemical and microbiota barriers as preventative mechanisms of pathogenic infection in animals and plants<|>Innate immune response including the steps in an inflammatory response and the characteristics and roles of macrophages, neutrophils, dendritic cells, eosinophils, natural killer cells, mast cells, complement proteins and interferons<|>Initiation of an immune response, including antigen presentation, the distinction between self antigens and non-self antigens, cellular and non-cellular pathogens and allergens
• Disease

  Any condition which impairs or has the potential to impair the functioning of an organism or part of an organism
• Types of disease

  • Infectious
  • Non-infectious
• Pathogen

  A disease causing organism/agent
• Types of pathogens

  • Cellular (living)
  • Non-cellular (non-living)
• Viroids have only been found in plants
• Bacteria

  Prokaryotic, not all are pathogenic, only a tiny percentage, classified on their shape, organisation, capsule, mobility, oxygen use, nutrition requirements and response to the Gram stain
• Bacterial toxins

  Exotoxins are secreted into the surrounding environment by bacteria<|>Endotoxins are internal components of a bacteria that become toxic when the bacterial cell is destroyed
• Bacterial diseases

  • Diphtheria - pseudomembrane and exotoxin
  • Cholera - uncontrollable diarrhoea leading to H2O loss, Vibrio cholerae
  • Pertussis - Bordetella pertussis
  • Tetanus - uncontrollable muscle spasms and death, Clostridium tetani
• Fungi

  Eukaryotic, important decomposers, not all are pathogenic, can be classified as multicellular or unicellular, cell wall composed of chitin
• Protozoa

  Unicellular, eukaryotic, usually motile, not all are pathogenic, heterotrophs that absorb nutrients from their host
• Parasites

  Eukaryotic and multicellular, organisms that grow and feed on an organism to the detriment of the host's survival, can be endoparasites (live inside host) or ectoparasites (live outside host)
• Pathogens

  • Numerous offspring
  • Hermaphroditism (don't need to search for a mate)
  • Suckers, hooks, claws (to attach and stay)
  • Piercing mouthparts (esp. vectors)
  • Life cycles involve more than 1 host
  • Vector transmission - long distances
  • Toxin/poison defence against host
• Virus

  Non-cellular (no cytoplasm or cell organelles), classified as non-living, require a host cell to replicate, all are pathogens, very small, each is usually highly specific to the host cell or organism it can infect, contain either DNA or RNA as their nucleic acid
• Generalised structure of viruses

  Genetic material (DNA or RNA)<|>Capsid (protein coat)<|>Some have an additional lipid membrane called an envelope<|>Some viruses which infect bacterial cells (bacteriophages) also have a tail
• Life cycle of viruses - infection of E. coli

  1. Attachment

  2. Penetration

  3. Uncoating

  4. Replication

  5. Assembly

  6. Release
• Life cycle of viruses - infection of animal cell

  1. Attachment

  2. Penetration

  3. Uncoating

  4. Replication

  5. Assembly

  6. Release
• Antibiotics do not work on viruses
• The only way to remove a virus is to kill the host cell
• Anti-viral drugs have been designed for some infections, however it is difficult to inhibit viral reproduction without interfering with the host cell metabolism
• Plant viruses

  Usually cause symptoms of stunting, dwarfing or discolouration in infected plants, spread from plant to plant via vectors such as insects, most contain RNA
• Viroids

  Smallest known infectious particles, very short pieces of naked RNA, currently only plant pathogens
• Prions

  Proteinaceous infectious particles only, non-living, protein pathogens that do not possess any genetic material (DNA or RNA), capable of replication and of causing infection, can be produced by mutations in genes coding for the normal cell protein or may enter the body in infected food
• Prions

  • Can cause normally folded proteins to refold into the abnormal form and hence propagate within a host body
  • Aggregate together to form amyloid fibres that cause holes to form in the brain (spongiform encephalopathy)
  • Have a higher beta-sheet content, making them more resistant to denaturation and difficult to treat
  • Generally very resistant to high temperatures, strong enzymes and UV light - making it very difficult to combat the infection
• Prions are believed to be responsible for Mad cow disease (BSE)
• Antibiotics

  Work by inhibiting bacterial cellular processes, such as prevention of cell wall being made, blocking bacterial ribosomes (so they can't make proteins), causing the breakage of bacterial DNA during replication (so they can't reproduce)
• Antivirals

  Need to target specific components of the virus that are as different to human proteins as possible (reduce side effects) and common across many viral strains
• First line of defence (barrier)

  Non-specific and has no memory, prevents the entry of pathogens in the first place
• Surface barriers in animals

  Intact skin protects external structures, contains biochemical defence agents, releases acidic secretions<|>Mucous membranes protect internal structures, contain biochemical defence agents such as lysozymes, may be ciliated to aid in the removal of pathogens
• Surface barriers in plants

  Mechanical barriers include waxy cuticle, epidermal cells, thorns/spines/prickles, cork layers, apoptosis<|>Chemical barriers include saponins, defensins, resins, tannins, gum, oils, irritants
• Surface Barriers - Plants

  Plants resist disease by producing chemicals that have antimicrobial properties
• Saponins

  A group of inactive compounds stored in vacuoles that may damage the cell membrane of pathogens when released
• Defensins

  Proteins which block the growth of pathogens and are typically released from germinating seeds
• Chemical Barriers

  Plants may additionally secrete a range of other anti-bacterial or anti-fungal agents, including resins and tannins<|>Some plants may secrete gum around infected areas, essentially sealing the area off (like a scab)<|>Some trees will produce oils that repel certain insect pests (and associated vector-borne diseases)<|>Some plants produce chemicals that are skin irritants (e.g. poison ivy or stinging nettles)
• Second Line of Defence

  Cellular (carried out by cells) and part of the innate immune response<|>Non-specific - the response is the same for all pathogens<|>No memory (non-adaptive) - produces the same response every time
• Circulatory System

  All blood cells (erythrocytes, leukocytes and platelets) are produced by multipotent stem cells in the bone marrow (via haematopoiesis)<|>White blood cells, (leukocytes), are transported to the sites of infection through the circulatory system
• Lymphatic System

  Is a secondary transport system that serves to protect and maintain the internal fluid environment by producing and filtering lymph<|>It is an open system<|>Lymph is a clear fluid that contains white blood cells (NO RED!) and arises from the drainage of fluid from the bloodstream and surrounding tissue<|>The fluid is filtered at points called lymph nodes - where pathogens are removed - before returning to the circulatory system<|>Lymph vessels contain valves to prevent the back flow of fluid<|>Major lymphatic organs include the spleen, thymus, tonsils and adenoids
• Inflammation

  A non-specific response to tissue damage caused by injury or infection<|>Characterised by pain, redness, heat, and swelling
• The Process of Inflammation

  1. Blood clot forms

  2. Chemicals released by damaged cells (e.g. histamines and prostaglandins) attract phagocytes to the infection

  3. Blood vessels increase in diameter and permeability in the area of damage. This increases blood flow to the area and allows defensive substances to leak into tissue spaces

  4. Phagocytes reach the damaged area within one hour of injury. They squeeze between cells of blood vessel walls to enter the region and destroy invading microbes

  5. An abscess starts to form after a few days. This collection of dead phagocytes, damaged tissue and various body fluids is called pus
• Mast Cells

  Twins of the basophils, except they are not a blood cells<|>Release granules of histamine to assist the action of immune cells and are responsible for allergy symptoms<|>Found in the lungs, skin, and linings of the nose and intestinal tract - these are the connective tissues