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Medical Microbiology (Subject) / Evasion of immune system (Lesson)
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- General methods Infection of non-phagocytotic cells (penetration of barriers, protection from immune system) production of spreading factors (invasion into deeper tissue, killing of host cells)
- Internalization strategies(Yersinia) 1. invasion alpha1-beta5-integrins 2. actin polymerization beneath bacterium 3. bacterial uptake by invagination of host cell membrane
- Internalization strategies (Salmonella typhi) 1.Injection of enzymes into host cell (Dephosphorilation of phosphotyrosine) 2.Rearrangement of cytoskeleton 3.ruffle formation (uptake of bacterium) 4.multiplikation inside phagosome (no proton pumps)
- Intracellular motility (Listeria monocytogenes) 1. internalin binds to E-cadherin (uptake of Bacterium) 2.Lysis of phagosome (lysteriolysin O) 3.Act A protein induces actin polymerization 4. enters neighbouring cells via propellation
- Spreading factors Hyaluronidase (Hyaluronic acid in connective tissue) Streptokinase (plasminogen into plasmin, dissolves blood clots) collagenase (breaks down collagen)
- Capsule prevents phagocytosis sialic or hyaluronic acid prevent antibody formation
- hydrophibic cell wall Mycolic acid 50% of cell wall protection against cationic proteins,lysosome,oxygen radicals
- Coating S.pyogenes (binds fibrinogen on M protein) S.aureus (binds collagen on Cna protein) effect: no antibodies can bind
- Enzymes vs antibodies IgA protease of Neisseria gonorrhoeae (cuts antibody) C5a peptidase of S.pyogenes (co factor) Protein A of S aureus binds antibodies wrong way (Fc side)
- Antigenic Variation changing of gene expression by homologous recombination synthesis of alternative surface proteins with similar function (adhesion) but different antigenicity
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- Surviving phagocytosis inhibition of fusion with lysosome inhibition of acidification of phagosome escape from phagosome