Immunology

• Immunology concerns the immune system and how it protects the body. It studies an organisms response to invasion by foreign microbes and their products.
• Even though we have approximately 1013 cells in our bodies, we have many more of other organisms living in or on the body. They include microbes such as fungi, protoctista and bacterial species.
• Many of these organisms cause disease in a parasitic relationship, such as by secreting toxins.
• Many though contribute to our health and defend us against disease in a symbiotic or mutualistic relationship. For example, Escherichia coli in the large intestine synthesises vitamin K, which is absorbed by the body.
• Pathogen


  An organism that causes damage to its host.
• Infectious


  A disease that may be passed or transmitted from one individual to another.
• Carrier


  A person who shows no symptoms when infected by a disease organism but can pass the disease to another individual.
• Disease reservoir


  Where a pathogen is normally found; this may be in humans or another animal and may be a source of infection.
• Endemic


  A disease which is always present at low levels in an area.
• Epidemic


  Where there is a significant increase in the usual number of cases of a disease often associated with rapid disease spread.
• Pandemic


  An epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.
• Vaccine


  Uses non-pathogenic forms, products or antigens of micro-organisms to stimulate an immune response which confers protection against subsequent infection through memory cells.
• Antibiotics


  Substances produced by microorganisms which affect the growth of bacteria.
• Antibiotic resistance


  Where a microorganism which should be affected by an antibiotic is no longer susceptible to it.
• Vector


  A living organism which transfers a disease from one individual to another.
• Toxin


  A chemical produced by a microorganism which causes damage to its host.
• Antigenic types


  Organisms with the same or very similar antigens on the surface. Such types are sub groups or strains of a microbial species which may be used to trace infections. They are usually identified by using antibodies from serum.
• Antigen


  A molecule that causes the immune system to produce antibodies against it. These may be individual molecules or those on the surface of cells.
• Antibody


  A protein produced by immune cells (B cells) which binds to a specific antigen
• Q1. How might E.coli benefit from humans?
• Important diseases you need to know about


  • Cholera
  • Tuberculosis
  • Smallpox
  • Influenza
  • Malaria
• Cholera


  • Toxins affect the human gut lining causing a watery diarrhoea, severe dehydration and frequently death.
  • Humans act as reservoirs or carriers and can contaminate water supplies with the pathogen.
  • Treatment of waste water, good hygiene and provision of clean drinking water.
  • Antibiotic treatment is possible but oral rehydration is the main method of treatment
• Tuberculosis


  • Most commonly affects lung and neck lymph nodes.
  • Symptoms include coughing, chest pain and coughing up blood.
  • It can be spread rapidly in overcrowded conditions and is transmitted in airborne droplets through coughing and sneezing of infected individuals in close proximity.
  • BCG vaccination programme for children.
  • A long course of antibiotics.
• Smallpox


  • Small blood vessels of the skin, mouth, throat and lungs causing a rash and blisters.
  • 30 to 60% fatality rate.
  • Airborne droplets of infected individuals in close proximity.
  • Now extinct due to immunisation programmes. This was possible due to low rates of antigenic variation/mutation. In addition, there was no animal reservoir and people were keen to be immunised because of the devastating effects of the disease.
• Influenza


  • Upper respiratory tract, causing a sore throat, coughing and fever.
  • Airborne droplets through coughing and sneezing of infected individuals in close proximity.
  • Quarantine and hygiene but difficult to control. Annual vaccination programmes, but due to new types this is not always effective.
  • Antibiotics are ineffective against influenza and are only used to treat the symptoms of secondary bacterial infection.
• Malaria


  • Liver cells and red blood cells, causing them to burst when more parasites are produced.
  • Symptoms include severe bouts of fever and flu-like illness, headache, muscle aches, and tiredness. Nausea, vomiting, and diarrhoea may also occur.
  • By a vector - a female mosquito from the genus Anopheles when feeding on blood.
  • Knowledge of life cycles. Nets, clothing & repellent. Vaccines difficult to develop. Drug treatment to reduce the chances of infection.

  
• Q1. Why are male mosquitos not vectors of the Plasmodium parasite?

  
• Plasmodium life cycle


  1. Plasmodium travels to, and then invades liver cells, where they mature.

  2. The infected mosquito takes a blood meal and the plasmodium parasite enters the blood stream.

  3. If a female mosquito were then to feed on the blood of an infected individual the Plasmodium parasites infect the mosquito, which act as a vector to pass the disease onto another host.

  4. Liver cells rupture and release plasmodium parasites. They then invade red blood cells and multiply asexually. Red blood cells then also rupture, releasing more plasmodium, which invade other red blood cells. The rupture of red blood cells results in severe fever.

  
• Q1. Why do you think vaccines have proved difficult to develop?
• Lytic cycle


  Viruses immediately reproduce using the host's metabolism to copy their nucleic acid and synthesise new coat protein (capsid). Once new viral particles (virions) have been assembled in the host cell cytoplasm, they will leave the host cell (so they can then infect new cells) in one of two ways: Lysis of the host cell e.g. common cold virus or Budding from the host cell surface (where the virus becomes enclosed by part of the host cell membrane) e.g. influenza virus
• Lysogenic cycle


  Following penetration of the host cell and shedding of the capsid, the viral nucleic acid is integrated into the host cell genome and may remain there for many cell generations with no clinical effect. The virus then enter the lytic cycle at some time later, which is when symptoms are produced e.g. Herpes simplex virus, HIV virus.

  
• Virus pathogenicity

  • Cell lysis: when viruses escape from cells to infect other cells / organisms (shedding)
  • Production of toxic substances
  • Cell transformation: viral DNA can integrate into the host chromosome. If the DNA inserts into a proto-oncogene or tumour suppressor gene it can result in the cell undergoing rapid and uncontrolled cell-division i.e. becoming cancerous.
  • Immune suppression
• Antibiotics


  A substance produced by a fungus which diminishes the population growth of bacteria
• Bacteriostatic


  Prevent the population growth of bacteria
• Bactericidal


  Kill bacteria
• Bacterial cell wall structure

  • Contains peptidoglycan consisting of molecules of polysaccharide cross-linked by amino acid side chains. This provides strength and prevents osmotic lysis.
  • In some bacteria this cell wall is surrounded by an outer layer of lipopolysaccharides.
  • The Gram stain reaction highlights cells with this additional layer (Gram negative) and they retain a counter stain and appear pink/red.
  • The presence of this extra layer provides Gram negative bacteria with protection from some antibacterial agents such as lysozyme and Penicillin.
• Tetracycline


  A broad-spectrum, bacteriostatic antibiotic that affects protein synthesis, a metabolic process common to all bacteria, and therefore is effective against a broader range of bacteria, including Gram +ve and some Gram –ve species. It acts as a competitive inhibitor preventing codon-anticodon complexes forming at the second anticodon-binding site on the 30S subunit of bacterial ribosomes and prevents the binding of a tRNA molecule to its complementary codon.
• Q. What effect would this have?
• Penicillin


  A narrow-spectrum, bacteriostatic antibiotic that affects the formation of cross-linkages in the peptidoglycan cell wall during growth and division of bacterial cells. It does this by binding to and inhibiting the enzyme (transpeptidase) responsible for the formation of these cross-linkages. Penicillin binds irreversibly to transpeptidase and it is not complementary to the active site of this enzyme. The enzyme's function is permanently altered.
• Using information from the text, explain what type of inhibitor penicillin is.