Disease & Immunity



  • Communicable disease are caused by pathogens and can be transmitted from one person to another. They are infectious.
  • Pathogenscan be transmitted directly or indirectly
  • Bacteria are prokaryotes that can usually damage cells directly or release toxins
  • Protoctists are unicellular eukaryotic organisms, which can produce sexually or asexually
  • Fungi are eukaryotic organisms which cannot photosynthesis therefore are parasites
  • Viruses are acellular, non-living particles, they can only replicate inside living host cells where they hijack the host machinery to replicate and then burst the cell to be released
  • Autoimmune diseases occur when the immune system mistakenly attacks its own antigens
    • In arthritis, antibodies attack membranes around the joints
    • In lupus antibodies attack proteins in the nucleus of cells
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Disease examples (Virus and Fungi)

  • HIV/AIDs
    • Virus
      • Attacks immune cells
  • Influenza
    • Virus
      • Attack mucous membrane in the respiratory system
  • Tobacco mosaic virus
    • Virus
      • Moult and discolour leaves on tobacco and tomato plants
  • Ringworm
    • Fungi
      • Causes a rash in cattle
  • Athletes foot
    • Fungi 
      • Causes a rash on the foot of humans
  • Black Sigatoka
    • Fungi
      • Causes leaf spots in banana plants
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Disease examples (Protoctista and Bacteria)

  • Blight
    • Protoctista
      • Affects potato tubers and tomato and potato leaves
  • Malaria
    • Protoctista
      • Bllod parasite Plasmodium spread by mosquitos
  • Tuberculosis
    • Bacteria
      • Kills cells and tissues, mainly in the lungs
  • Bacterial Meningtis
    • Bacteria
      • Causes swelling of the meninges damaging the brain and nerves
  • Ring Rot
    • Bacteria
      • Decays vascular tissue in tomato and potato plants
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Cell-mediated Immunity

  • Antigens from the pathogen is displayed on the cell surface of body cells or phagocytes after phagocytosis
    • Antigen Presenting Cells (APC)
  • T cells with the correct specific receptor bind with the antigen and are activated
  • They divide by mitosis (clonal expansion) and differentiate into T helper, cytotoxic and memory cells
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Primary & Secondary Response

  • The primary immune response is when a pathogen infects the body for the first time the initial immune response is slow
  • They secondary immune response is a more rapid and vigourous response caused by a second or subsequent infection by the same pathogens. This is due to the presence of memory cells

                                      Image result for primary and secondary immune response

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Components of the Immune System

  • Antigens are any part of an organism/substance which is recognised as foreign by the immune and goes on to trigger an immune response
  • Phagocytes
    • Macrophages
    • Neutrophils
      • Engulf and digests pathogens by fusions of the phagosomes with lysosomes
  • T cells
    • T helper cells
      • Stimulate B cells to divide an secrete antibodies
    • Cytotoxic T cells
      • Kill abnormal cells and infected body cells via perforin
    • T memory cell
      • Remain in the blood for years and provide long term protection
  • B cells
    • Plasma cells
      • Secrete antibodies
    • B memory cells
      • Remain in the blood for years and provide long term protection
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Components of the Immune System continued...

  • Antibodies are a protein produced by lymphocytes in response to the presence of the corresponding antigen
  • Antibodies agglutinate pathogens by forming antigen-antibody complexes, leading to phagocytosis & neutralise toxins 

                                          Image result for antibody

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  • Human primary defences include
    • Skin acting as a barrier
    • Blood clotting and Skin repair
    • Mucous membranes
    • Coughing and sneezing
    • Inflammation
  • Plant passive defences include:
    • Cellulose barrier
    • Lignin
    • Waxy cuticle
    • Bark
    • Callose blocking flow in sieve tubes
  • Plant defences include
    • Deposit callose
    • Close stomata
    • Add cellulose
    • Induce cell necrosis
    • Increase the number of oxidative bursts
    • Produce chemical defences
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Defences continued...

  • Phenois
    • Antibiotic and antifungal proteins. One example is the tannins present in tree bark
  • Alkaloids
    • Compounds containing nitrogen are bitter to stop herbivores feeding on them and affect enzyme action
  • Defensins
    • These cysteine-rich, defensive proteins have anti-microbial activity. They appear to affect the functioning of ion transport channels in the plasma membrane
  • Hydrolytic enzymes
    • Present in the spaces between cells, they can have a variety of effects. Chitinases break down the chitin in fingal cell wall, glucanases hydrolyse the glycosidic bonds in glucans, and lysosomes destroy bacterial cell walls
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Humoral Immunity

  • The humoral response is the best at fighting pathogens which are free in the bodily fluids
  • Free antigen binds to a complementary B cell receptor, activating the B cells (Clonal selection)
  • The pathogen is endocytosed, and the antigen presented on the plasma membrane
  • T helper cell binds to the presented antigen and stimulates the B cell to divide by mitosis (Clonal Expansion)
  • The B cell differentiates to plasma and memory cells
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Vaccination & Medicines

  • Vaccination is the introduction into the body of a vaccine containing disease antigens, by injection or mouth, in order to induce artificial immunity
  • Vaccines work by injecting weakened/dead pathogens into the body to stimulate an immune response, to form memory cells against the specific antigen, which destroy the pathogen quickly upon the infection
  • Herd immunity is when the vaccination of a significant proportion of the population provides protection for individuals who have not developed immunity
  • Pathogens may mutate so their antigens change suddenly (antigenic variability). So the vaccine is now ineffective to the new antigens
  • Ethical considerations: side effects, financial cost, right to choose, animal testing of vaccines, human trials
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Vaccination & Medicines- Different types of immuni

  • Active immunity occurs when specific antibodies are produced by the individual's own immune system
  • Passive immunity occurs when a specific antibodies are introduced to the individual from an outside source
  • Natural Active
    • Direct contact with pathogen
  • Natural Passive
    • Antibodies through breastmilk
  • Artificial Active
    • Vaccination
  • Artificial Passive
    • Injection of antibodies
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Vaccination & Medicines- medicines

  • Antibiotics prevemt the growth of bacteria. They are effective because they show specificity in killing bacteria without harming human cells. However, overuse has led to the spread of resistance in bacteria e.g. MRSA. 
    • To reduce spread prescription of antibiotics is controlled, patients must finish their course and prevent spread by control measures
  • New medicines can be discovered form plant compounds using DNA sequencing to screen plants and organisms for potential medical compounds. DNA sequencing can also be used to develop a specific drug suited to persons genome
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