Immunology and Infectious Disease: Week 1 Study Guide

Immunology and infectious disease week 1 SAQ study guide questions 1. Discuss the ways in which the complement system can be triggered (3 marks) Answer: The complement system is used to enhance the functions of phagocytic cells and antibodies. The complement system can be activated in three different ways: - Classical pathway: antigen and antibody interaction Alternate pathway: complement proteins binding to microbial surface antigens. Mannose-binding lectin pathway: plasma lectin binding to microbial antigens 2. What are happens once the complement system is triggered? (3 marks) Answer: • • • Formation of membrane attach complexes: create wholes within the bacteria and its cell wall causing it to lysis. Opsonisation: coat bacterial surfaces to enhance the ability to phagocytosis cells to phagocytose them Inflammatory cytokine release to attract immune cells to the target location (site where the microbes are located at) 3. Explain the primary and secondary lymphoid organs (3 marks) Answer: • • Primary lymphoid organs are where immune cells arise from and mature. These are: Red bone marrow: in there the process of haematopoiesis takes place making immature T and B cells. In the red bone marrow, B cell maturation takes place. Thyroid: these is where T-cell maturation takes place Secondary lymphoid organs: this is where antigen presentation and fighting takes place. These organs include lymph nodes, liver, spleen, and lymphoid tissue. It is in these places where immune cells such as macrophages, CD8+ cells, B plasma cells etc. fight off foreign and harmful microorganisms, such as bacteria. 4. Explain how bacteria can cause fever. (3 marks) Answer: • • • • • • Macrophage digests bacteria via endocytosis forming a phagosome. Phagosome fuses with lysosome forming a phagolysosome. Bacterial lysis takes places leading to the release of endotoxins. Endotoxins triggers the release of the cytokines IL-1 and tissue necrosis factor alpha (TNFalpha) These cytokines will go to the brain to the hypothalamus stimulating the release of prostaglandins. This will lead to resting the body’s thermostat to a higher one leading to fever. 5. Discuss the role of interferons and their mechanism of action (4 marks) Answer: Interferons are enzymes made in response to a viral infection. They are cell specific but not viral specific. Their role is disturbing viral replication. When a cell encounters a virus, it synthesises interferons (INF). INF cannot act on that cell or any other infected cell. Rather, they go and bind to healthy uninfected cells and stimulate the production of antiviral proteins. Moreover, it will increase the synthesis of MHC molecules which enhance susceptibility to natural killer cells and cytotoxic cells. When those uninfected cells are infected by the virus, since those cells now have antiviral proteins, these proteins will work to disturb viral replication of the cell. 6. Dr. Aisha is seeing a 10-year-old patient – Anna. Who has a fever. Upon further investigations it is found that Anna is infected with streptococcus pyogenes a. Explain at the cellular level how this pathogen causes fever and what is the significance of fever in this case (4 marks) b. Describe the mechanism of action of streptococcus pyogenes. (3 marks) c. Explain how the immune system will react to this pathogen, given that this is the first time the body has an infection from it. (6 marks) Answer: a. Macrophages will take in the bacteria via endocytosis forming a phagosome within the macrophage. The phagosome will fuse with the lysosome forming a phagolysosome. This will lead to intercellular destruction and lysis of the bacteria. This will cause the bacteria to release endotoxin. In response to the endotoxins, the cytokines IL-1 and tissue necrosis factor alpha will be released. These will travel through the blood stream, into the brain into the hypothalamus, rest the body’s thermostat to a higher temperature, thus causing fever as a result. b. On its’ Streptococcus pyogenes has protein M. Protein M allows it to attach to host cell (note: attachment to the cell not entry into the inside of the cell). Following, this will trigger the release of hyaluronidase, which is a form of toxin. It will destroy hyaluronic acid, thus destroying the tight linkages between blood vessels and connective tissue. This will allow the bacteria to pass through, and lead to local inflammation. c. To be done later 7. Compare and contrast positive and negative gram bacteria (4 marks) Answer: • • Positive gram only features. Stains blue Only has an inner membrane. Thick peptidoglycan layer Has lipoteichoic acid Negative gram only features. • - Stains pink/red Has both inner and outer membranes Has polysaccharides More likely than positive gram to have pilots. Periplasmic space present (separates inner and outer membranes) Both negative and positive Cell wall Capsule Flagella 8. List and describe the FOUR subtypes of acute inflammation (4 marks) Answer: • • • • 9. Serous: exudate of poor cell fluid Suppurative: mixture of living and non-living (dead) neutrophils with products of tissue digestion to form puss. Fibrous: large vascular leaks -> fibrinogen leaks out -> forms fibrin -> becomes fibrous Ulcerative: local defect at surface or excavation at the surface of the tissue or organ Compare and contrast the outcomes of acute and chronic inflammation (4 marks) Answer: • - Acute: In severe cases death (sad) Chronic inflammation Complete resolution where vascular and cellular inflammatory events are restored, function returns as usual. So, things return as perfect as before. - Partial resolution: there is a scar due to healing with fibrosis, however, function may not be as before. • Chronic - Death if severe - Fibrosis (fibrotic tissue) where a part of the organ or the whole organ may just stop functioning (organ/tissue become inactive) - Chronic disability: patient dies with disease BUT NOT from disease. - Persists, spreads all over body and become fatal. 10. Explain the differences between the three types of UV. Answer: • • - UVA Highest wavelength Lowest energy levels Penetrate though windows and clouds. Damage deeper than UVB Most common type used in tanning beds. UVB Lower wavelength than UVA but higher than UVC Higher energy level than UVA but lower than UVC • - Cannot penetrate through windows and clouds. Direct damage to DNA UVC Lowest wavelength Highest energy levels Penetrated by ozone layer thus cannot reach most parts of earth, as where the ozone hole is it can pass though. Most dangerous