Phase 1 - Week 2 (Immunology, Bacteria/Viruses) Flashcards
What is the basic function of cytotoxic T cells?
Kill infected cells by apoptosis
How do bacteria cause infection in humans?
Once bacteria enter a new host they multiply (if conditions are favourable) and many produce toxins which cause the development of disease symptoms. Many disease symptoms are cause by the host’s immune response to the bacteria.
What determines the rate at which bacteria grow and divide?
The nutritional status of their environment
How is viral messenger RNA synthesised in RNA viruses?
Must use their own polymerase which may be carried in the nucleocapsid
Empirical therapy
- Best educated guess therapy based on clinical/epidemiological acumen
- Used when therapy cannot wait for culture - more severe infection (e.g. sepsis, meningitis)
- Need to cover all likely causes
- Broad spectrum - impact on colonisation + resistance may be greater
Memory T cells
Can survive for years and allow for rapid response to pathogen if detected in second immune exposure
Describe the steps in replication of a virus
- Synthesis of viral messenger RNA (direct or via host machinery)
- Synthesis of viral protein for new capsids
- Synthesis of viral nucleic acid
Why are viruses still a medical problem?
Large population diversity + fast evolution - can exchange genetic material and mutate rapidly.
Bacteriostatic antibiotics
Suppress growth but does not directly sterilise infected site. Requires additional factors to clear bacteria - immune mediated killing.
Describe the phagocytes involved with the 2nd line defences of the Innate immune response
Monocytes which mature into macrophages/neutrophils
Describe the action of antibodies
- Secreted into circulation/mucosal surfaces
- Neutralise/eliminate microbes
- Neutralisation - prevent pathogens from entering or damaging cells by binding to them
- Opsonisation - coat pathogen to target it for removal by phagocytosis
- Complement activation - cascade of protein production that either opsonise protein for phagocytosis or lyse it directly by forming a membrane attack complex (MAC)
Why are bacterial infections harmful/difficult to treat?
Bacteria have short lifespans and produce large numbers of offspring so can quickly adapt to changing conditions. They can evolve to adapt to new hosts or become resistant to treatments and medicines such as antibiotics.
Describe factors which contribute to the inflammatory response
- Vasodilation - mediators e.g. prostaglandins, capillary widening causes increased blood flow resulting in redness + heat, allows movement of WBCs to injured area
- Increased vascular permeability - mediators e.g. histamine, allows leaking of fluid containing WBCs out of blood vessel to site of injury
- Attraction of WBCs (chemotaxis) - mediators e.g. Leukotriene B
- Systemic response - fever, proliferation of WBCs
List the methods of transfer of genetic material
- Transformation - genetic material taken into bacterium through membrane
- Transduction - uses a bacteriophage
- Conjugation - pilli connect bacteria allowing for plasmid transfer
Neutrophils
- Abundant in blood
- Phagocytise pathogens in acute inflammation
- Contain lysosomes to digest the microbe
- Release soluble mediators
- Short lived
- Contain bacteriostatic and toxic factors
How is viral mRNA translated?
In host cytoplasm using ribosomes to synthesise viral proteins
Gram negative
The peptidoglycan layer is thin and is overlaid by an outer membrane, anchored to lipoprotein molecules in the peptidoglycan. When a gram stain is applied the thin layer will not hold the stain in the cell so it is not stained purple - another stain is applied which stains it pink.
Dendritic cells
Antigen-presenting cells which have MHC class II proteins. They mature from monocytes in the blood.
Explain how microbiological barriers contribute to the 1st line defences of the Innate immune system
Normal flora of the gut/skin prevent pathogens from dividing
Bactericidal antibiotics
Acheive sterilisation of the infected site by directly killing bacteria. Lysis of bacteria can lead to release of toxins and inflammatory material.
Explain how dendritic cells link the innate and adaptive immune system
Antigens from pathogens must be in/on MHC proteins to be recognised by T cells, so dendritic cells take in and present the pathogens and are transported to the lymph nodes via lymph drained from the infected tissue, where they activate specific T cells. Their movement is stimulated by chemokines.
Describe the target effects of an antibiotic
- Highly toxic to bacteria causing infection
- Penetrate body area affected by infection
- Limit release of toxins from bacteria
- Convenient administration
Explain how chemical barriers contribute to the 1st line defences of the Innate immune system
- Acid secretions in the stomach
- Lysozyme enzyme in tears/saliva
- Low pH of skin due to sweat secreted by eccrine glands
Pilli
More rigid that flagella - function in attachment either to other bacteria or to host cells
Prophylactic therapy
- Preventing therapy before it begins
- Healthy people exposed to surgery/injury/infected material
- Immunocompromised - HIV, transplantation, splenectomy
Describe the methods by which viral particles can be released following assembly
- Budding through cell membrane - will acquire envelope
- Released following cell death
- Released following cell lysis
What is the basic function of B lymphocytes?
Mature into plasma cells which produce antibodies
Describe antibiotic resistance mechanisms
- Mutation of target site
- Inactivating enzymes
- Limit access - reduced permeability, increased efflux
Genes mediating resistance can often by easily trasnsferred
Describe how retroviruses synthesise new viral DNA
- Virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome
- DNA is incorporated into the host cell genome by an integrase enzyme
- The host cell then transcribes + translates the viral DNA, producing the components required for new viral particles
Guided therapy
- Identify cause of infection and select agent based on sensitivity testing
- Used for mild infections that do not need to be immediately treated/to rationalise therapy in patients already on therapy
- Narrow spectrum - achieve clinical cure with little impact on colonisation + resistance
How to bacteria obtain nutrients?
Mainly by taking up small molecules across the cell wall
How is viral messenger RNA synthesised in DNA viruses?
mRNA is formed using the host’s RNA polymerase to transcribe directly from the viral DNA
Explain the mechanism of action of Cytotoxic (CD8) T cells
- Recognise antigens on infected cells
- Induce death of cells - bind, induce cell death (apoptosis) by punching holes in cell membrane using perforin
- Prevent pathogen (e.g. virus) from spreading - sacrifice infected cells