microbial evasion stratergies

• importance of immune system:

  • pathogen defence - detection and elimination of pathogens to prevent infection
  • cancer surveillance - recognition and elimination of abnormal cells
  • tissue repair - repair and healing of sites of damage
  • memeory for future protection: immunological memory helps for faster and more effective response upon subsequent exposure of the same pathogen
• key evasion stratergies:

  • antigenic shift (shift and drift)
  • intracellular survival
  • escape from a phagocytosis
  • biofilm phagocytosis
  • immunosuppression
  • molecular mimicry
• antigenic variation is the ability to alter surface antigens over tome preventing the immune system from developing long-lasting defences
• immune system relies on recognition of specific antigens in order to mount a targetted immune response against pathogens
• antigenic variation is a survival stratergy to alllow microbes evade the immune system and be able to persist for longer periods of time
• mechanisms of antigenic variation:

  • gene rearrangement
  • hypermutation
  • recombination
• gene rearrangement is when the possession of multiple genes coding for surface proteins can be rearranged to produce different antigenic variants
• hyermutation is rapid mutation in specific regions of microbial genome leading to generation of diverse antigenic forms
• recombination is the exchange of genetic material between different strains or species resulting in new antigenic combinations
• intracellular survival is the ability of microorganisms to exist and multiply within the host cell which includes immune cells without being eliminated
• intracellular survival allows microbes to exploit the host cells resources for replication and potentially establish chronic infection
• muechanisms of intracellular survival:

  • invasion of host cells
  • escape from phagosomes
  • avoidance of immune recognition
  • replication within host cells
• invasion of host cells can involve specialised adhesins with host cell receptors which controls the entry of pathogens into the host cell
• escape from phagosomes allows pathogen to avoid destruction by the host cells lysosomal enzymes
• avoidance of immune recognition can involve inhibiting presentation of antigen in cell surface which interferes with the host cells signalling pathways or modulate the expression of surface antigens
• replication within the host cell in order to exploit host cells mechanisms to replicate more microbial particles with some pathogens even causing the formation of specialised structures within the cell in order ti form a protected environment for replication
• forms of escape from phagocytosis:

  • inhibition of phagosome formation
  • survivial within phagocytes
  • escape from phagosomes
  • antiphagocytic factors
• inhibition of phagosome formation is doen by interfering with the signaling pathways involved so these pathogens can avoid being internalised by phagocytes
• cetain pathogens have evolved to have function that allow them to survive after being internalised by the phagocyte by persisting again microbial activities such as changes in pH, digestion by enzymes which allows them to persist
• membrane disruption/manipulation of the memebrane can allow pathogens to evade phagocytes
• antiphagocytic factors is when pathogens may produce molecules which inhibit the pagocytic activity of immune cells which can include capsules making it harder for the pathogen to be engulfed or other surface proteins that itnerfere with recognition and binding of pathogen by phagocytes
• pathogens can imitate host cells which makes it harder for the immune system to recognise and produce an effective response
• mimicry includes:

  • molecular mimicry
  • immunomodulation
• molecular mimicry is when pathogens produce molecules that structurally resembles host molecules
• immunomodulation is when pathogens may produce molecules which interfere with the hosts immune signaling pathways or cytokines which influences the immune response