Immunology

• What's a pathogen?

  An organism that causes disease in its host
• What is an endemic?


  A disease which is always present in at low levels in an area.
• What is an epidemic?

  A significant increase in the usual number of cases of a disease associated with a rapid disease increase
• What is a pandemic?

  An epidemic crossing international boarders and infecting a large number of people.
• What is a disease?

  The body acting as a host to another living organism.
• How does E.coli benefit from humans?

  • Gains nutrients
  • Gains protection
  • Provided with optimum pH and temperature
• Cholera

  • Pathogen = vibrio cholerae (gram negative bacterium)
  • Site of infection = human gut lining
  • Symptoms = Diarrhoea, severe dehydration and death
  • Mode of transmission = drinking contaminated water that have been contaminated by humans reservoirs
  • Prevention and control = treatment of waste water, good hygiene, provision of clean water and vaccines
  • Treatment = antibiotic treatment and oral rehydration
• Tuberculosis

  • Pathogen = mycobacterium tuberculosis (bacterium)
  • Site of infection =lungs and lymph Nodes
  • Symptoms = coughing, chest pain and coughing up blood
  • Mode of transmission = airborne droplets through coughing and sneezing of infected individuals in close proximity
  • Prevention and control = BCG vaccination programme for children
  • Treatment =long course of antibiotics
• Small pox

  • Pathogen = virola major (virus)
  • Site of infection = small blood vessels pf skin, mouth, throat, lungs
  • Symptoms = rash and blisters with 30% to 60% fatality rate
  • Mode of transmission = airborne droplets of infected individuals in close proximity
  • Prevention and control = extinct due to immunisation programmes that were possible due to the low antigenic mutation rate with no animal reservoir
• Influenza

  • Pathogen = 3 subgroups such as H1N1 (virus)
  • Site of infection = upper respiratory tract
  • Symptoms = sore throat, coughing and fever
  • Mode of transmission = airborne droplets through coughing and sneezing of infected individuals in close proximity
  • Prevention and control = quarantine, hygiene and annual vaccination programmes which are not always effective due to the new types
  • Treatment = rest, warmth, fluids and painkillers
• Malaria

  • Pathogen = plasmodium (protoctista)
  • Site of infection = liver and red blood cells which burst when more parasites are produced
  • Symptoms = severe fever, headache, muscle aches and nausea
  • Mode of transmission = female anopheles mosquito feeding on blood as a vector
  • Prevention and control = nets, clothing, repellents and drug treatments to reduce chances of infection since vaccines are difficult to develop
  • Treatment = drugs that affect plasmodium outside cells but are limited sucess and have side effects
• Why are male mosquitos not vectors of malaria?

  They feed on nectar and not blood.
• Describe the malaria life cycle

  1. Infected Mosquito takes a blood meal and plasmodium parasite enters human bloodstream
  2. Plasmodium travels and invades liver cells where it matures
  3. Liver cells rupture and release parasites which reach blood cells and multiply asexually
  4. Red cells burst releasing more parasites causing more blood cells to burst causing a fever
  5. Female mosquito feeds on the blood of infected human and the plasmodium infects mosquito making it a vector
• What are some ways to respond mosquito behaviour to prevent malaria?

  • Sleep under nets = mosquitos feed at night
  • Nets treated with pyrethroid insecticide = kills mosquitos
  • Spray walls with insecticide = kills mosquitos since they rest on walls after feeding
  • Drain/cover stagnant water = removes the female mosquito access to egg laying sites
  • Film of oil on water = prevents larvae piercing surface to obtain oxygen
• What are some biological control methods to prevent malaria?

  • Fish introduced into water = fish will eat aquatic larvae
  • Infecting mosquitoes with bacterium = bacterial infection blocks plasmodium development
  • Male mosquito determined with X rays = no offsprings can be produced
• Why have malaria vaccines been difficult to produce?

  Plasmodium parasite has a higher mutation rate with many antigenic types
• Why are virsues describes as being inert?

  They're particles with no metabolic pathways.
• Describe the lytic cell

  1. Viruses reproduce using the host cells metabolism to copy their nucleic acids and synthesise an new capsid
  2. Once the new viral particles (virons)have been assembled in the cytoplasm, they will leave the cell to infect other cells by:

  • Lysis of the host cell (common cold)
  • Budding from the host cells surface (influenza)
• Describe the lysogenic cycle

  1. Virus penetrates host cell and synthesise a new capsid
  2. The viral nucleic acids integrates itself into the host cells genome and may remain there for generation with no clinical effect
  3. Virus enters lytic cycle which produces symptoms
• How can Viruses be pathogenic ?

  • Cell Lysis when Viruses escape host cell
  • Production of toxic substance
  • Cell transformation when viral DNA integrates into host chromosomes. If the DNA inserts itself into a proto-oncogene or tumour suppressor gene is can result in uncontrolled cell division (cancer)
  • Immune suppression
• What is an antibiotic?

  A substance produced by fungus which diminishes the population growth of bacteria
• What are the two types of antibiotics?

  • Bacteriostatic = prevents the population growth of bacteria
  • Bactericidal = kills bacteria
• Why do antibiotics not cause any harm to patients?

  They only act on bacteria but not eukaryotic cells or viruses.
• What are broad spectrum antibiotics?

  Acts against a wide range if infections as it targets both gram positive and gram negative bacterial group.
• What are narrow spectrum antibiotics?

  Act against a selected group of infections as they target either gram positive or gram negative but not both.
• What is the structure if bacterial cell walls?

  • Peptidoglycan walls consisting of polysaccharide molecules cross linked by amino acid chains
  • Gram negative bacteria have a thin layer of peptidoglycan and an additional layer of lipopolysccharides which retain a pink counter stain in the gram stain reaction
• What is the function of of peptidoglycan?

  Provides strength and prevents osmotic lysis.
• What is the function of the extra layer of lipopolysccharides?

  Protection from some antibacterial agents such as lysozyme.
• How does tetracycline act against bacterial infections?

  • Inhibits protein synthesis in both gram negative and positive bacteria
  • It blocks the second tRNA binding site in the large subunit of the ribosome which prevents the tRNAs antibodies from binding to its complementary codon, stopping translation
• How does pencillin act against bacterial infections?

  • Affects the formation of cross links in the peptidoglycan cell wall during grown and division of bacterial cells
  • Binds irreversibly to transpeptidase even though it isn't complimentary to the active site which permanently alters the enzymes function
• Why are gram positive bacteria more susceptible to pencillin?

  Due to their thick peptidoglycan cell wall.
• How do bacteria become antibiotic resistant?

  1. Bacteria divides under optimum condition and have a high mutation rate which gives them an advantage in the presence of antibiotics
  2. Plasmids containing the antibiotic resistance allele can be transfered across bacterium via conjugation
• How does the overuse of antibiotics results in resistance?

  Resistant bacteria only have a selective advantage when the antibiotic is present so overuse of these antibiotics increases the frequency of the resistence allele.
• What are some examples of bacteria that are resistent to antibiotics?

  • Leprosy
  • Gonorrhea
  • MRSA
  • tuberculosis
  • Clostridium difficile
• What are the non specific immune responses?

  • Ciliated mucus membranes = mucus traps microorganisms and cilia wafts them up and out of trachea
  • Blood clotting = prevents entry of pathogens into broken capillaries
  • Localised inflammation
  • Skin = tough barrier
  • Skin flora = bacteria and fungi offer competition for pathogenic bacteria as they do not wash off as easily
  • Tear ducts and saliva = lysozyme hydrolyses peptidoglycan walls of bacteria
  • Stomach acid = kills bacteria
• Describe the process of the humourless repsonse

  1. B lymphocytes originate from stem cells in the bone marrow and mature in the spleen and lymph Nodes
  2. Millions of B cells circulate in the blood and lymph, having specific receptor on its surface which binds to one type of antigen
  3. When a foreign antigen enters the specific B cells bind to the foreign antigen
  4. This activates the B cells to divide by clonal expansion to form:
  5. Memory B cells = remain dormant in the blood until the same antigen is encountered in the future
  6. B Plasma cells = secret antibodies specific to antigen
• What is the structure of an antibody?

  • Y shaped globular protein
  • quaternary structure as they are made of four polypeptide chains
  • Has two antigen binding sites
  • peptide bonds between amino acids
  • hydrogen bonds, disulphide bridges and ionic bonds between r groups
• What is the function of antibodies?

  To bind to specific antigen to from an antigen antibody complex where they render the antigen inactive by agglutination which allows phagocytes to locate and engulf the Pathogen.

  Antibodies can also bind to toxins and undergo agglutination of toxins to render then inactive
• What is agglutination?

  The clumping together of bacteria.
• Label the structure of the antigen

  1. Variable region
  2. Constant region
  3. Heavy chain
  4. Light chain
  5. Disulpuide bridges