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27 Cards in this Set
- Front
- Back
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How can a pathogen evade or suppress complement?
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1)Polysaccharide Capsules can result in complement failing to activate as it cannot bind 2)Acceleration of breakdown 3)Block MAC function - capsules allow physical barrier to membrane of pathogen |
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How can 'acceleration of breakdown' in Influenza, S.pyogenes & N.gonorrhoea prevent complement?
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-H.influenza: C5a peptidase breaksdown C5a component - S.pyogenes: M protein binds c4b binding protein - N. gonorrhoeae- immobilised factor H, favours C3b breakdown |
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How can pathogens avoid cytokines? |
1) Inhibiting cytokine production, e.g. Hep B inhibits IFN alpha production 2) Inhibiting cytokine receptor expression, e.g. Trypanosoma cruzi downregulates IL-2receptor expression. 3) producing a (soluble) protein that binds to cytokines and renders the cytokines useless. |
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Whatare 3 functions of the bacterial polysaccharide capsule? |
· Prevent phagocytosis · Stop complement binding Prevent PRR binding |
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How does legionella pneumophila avoid phagocytosis?
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allowsphagocytosis but once it is in the phagosome, it forms a protein channel and injects many effector proteins into the cell.Effects include blocking of phagosome-lysosome fusion and inhibition of innatedefences. |
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How does staphylococcus aureus avoid phagocytosis? |
has a protein called protein A – it is an Fc receptor.Instead of the Fc region binding to the macrophage, it binds to the bacteria,which means they become functionally impaired. Herpes simplex has an Fcreceptor (as part of their genome) and the same thing occurs |
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Outline 3 ways of avoiding adaptive immunity. |
1) Concealment.This involves staying in an area of the body that is immunologicallyprivileged. 2) Antigenic variation. Microorganismscan express a different variantsurface glycoprotein VSG,which means the antibody cannot bind (as it is specific). Antigenic drift or antigenic shift 3) Immunosuppressione.g. HIV, suppresses T cell immunity. |
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What is antigen drift and what is antigenic shift? |
Antigenic drift = accumulation of mutations within genes that code for antigens
Antigenic shift= 2 or more different strains of a virus combine to form a new subtype with a mixture of the surface antigens of the orignal strains |
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How does influenza avoid the adaptive immune system? |
Mutates its surface antigens and/or recombines parts of its genome with other viruses. It avoids the adaptive immune system through antigenic change which occurs by point mutation & by reassortment |
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How can viruses carry out active suppression of antigen presentation? |
Viruses can produce proteins thatprevent the presentation of the antigenfragments in APCs. Strategies include making proteins for:· -Blocking TAP, preventing transport ofviral peptides into the ER - Binding to MHC class I, keeping it inthe ER. Manyviruses target MHC class I expression (at different stages of the endogenouspathway). |
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Describe the 3 forms of fungi and give examples of some species in thecategories.
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· Yeasts. These are single-celled, budding organisms, e.g. Candida albicans orCryptococcus neoformans. · Moulds. These are organisms with branching hyphae, e.g. Aspergillus fumigatusor Trichophyton rubrum. · Some species are capable of displaying bothmorphologies in response to environmental triggers and are, therefore, termed dimorphicfungi e.g. Histoplasma capsulatum or Penicillium marneffei. |
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What is the main sterol in fungi cell membranes?
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Ergosterol |
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Describe the cell wall structure of fungi
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a cell wall with sugar chains that are crosslinked. It consists ofseveral types of polysaccharides (glucans, mannans), proteins and chitin (a tough polymer that providesstrength). Some fungi have melaninin the cell wall. |
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Do fungi have capsules? |
Some fungi have polysaccharide capsules, e.g. Cryptococcus neoformans
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What is a fungal spore? |
= basic reproductive structure of fungi |
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What is a hypha? |
Growth of fungal spore
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What is a mycelium? |
The collection of interwoven hyphae is known as a mycelium. |
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What happens in candida infections?
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- overgrowth of colonising flora - epithelial barrier is being disturbed- moist & warm - breakdown in natural integrity of the epithelial barrier Causes "thrush" is an opportunisitic fungal infection |
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What is parasitism?
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Activity of an organism that spends any portion of its life in direct contact with a host species at the expense of the host Paraistes are eukaryotes |
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What are the 3 main groups of parasites?
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Protozoa- intra& extracellular, can exist in all body compartements Helminths- multicellular, highly organised, complex life cycles Ectoparasites - external to the body, e.g. insects, arachnids |
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How is trichomonas vaginalis (parasite) transmitted? |
Sexually transmitted through mucosal surfaces which are not very hostile, directness of contact means it does not need cyst formation |
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How are parasites transmitted? |
1) Contamination of environment/behavioural changes in the host. Associated with resistance cyst or ova which can survive in the environment 2) Consumption of resistant stages with food, e.g. tissue cyst f toxoplasma 3) Direct invasion e.g. schistosomes & hookworms |
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Describe the giardia lamblia parasites |
- Many are zoonotic (parasites of animals which are transmitted to humans) - Temperate parasite which is primarily found in beavers in north america - zoonosis - Tranmission via water supplies & faecal oral route - Cyst has a tough outer surface which protects the parasite that is triggered to burst in the pH of the stomach |
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Describe trichomonas vaginalis (parasite)
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- Causes inflammation & damage leading to secondary bacterial infections in the vagina - Has membrane containing nucleus, cytoplasm & flagella - Once it is taken away from mucosal surfaces & put in water, it bursts |
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Describe toxoplasma (close relative of malaria)
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- Obligate intracellular parasite - Acute-flu like phase - Latent or quiescent phase- form large tissue cysts within the brain where it is latent in quiescent stage of its life cycle, with lipid stores, until the host is immunosuppressed at which point it ruptures |
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What are the mechanisms of pathogenesis for parasites? |
-Disruption of normal physiological function, e.g. giardia causes uptake & metabolism of bile which induces malabsorption - Invasion of host tissue - Toxoplasma & Leishmania invasion of macrophages - physical presence - induction of immune responses. e.g. leishmania lesions associated with protective immune response. Toxoplasma encephalitis associated with cyst reactivation |
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What are ectoparasites? |
- e.g. flees, ticks, head lice etc. |
