Microbial Immune Evasion Mechanisms Flashcards
What are adhesions, toxins and capsules?
- Adhesions – allows adherence to the surface of the body
- Toxins – cause tissue damage
- Capsules - block the attack of the immune response
What are the 4 properties of the host?
- Natural barriers
- Defensive properties
- Complement
- Immune response
What are the 3 virulence factors?
- Promote colonisation and adhesion to establish infection
- Evade host defences
- Promote tissue damage
What aspects of immunity have pathogens evolved to overcome or avoid?
• Natural defences – mucosal layers, skin
• Innate immunity such as the complement system and macrophages
• Adaptive immunity – antigen specific and memory
o Antibodies
o T-cells – CD4 and cytotoxique T-cells
What do pathogens do to the complement system?
Failure to trigger binding of complement proteins
Disrupt regulation block/ expel MAC
Roles of complement?
- induces inflammatory response
- promotes chemotaxis
- phagocytosis by opsonisation
- Increase vascular permeability
- mast cell degranulation
- lysis of cell membranes
Give 3 intracellular pathogens
- e.g. Mycobacterium tuberculosis
- Listeria
- Salmonella
hidden from serum killing, complement, antibodies
How do pathogens prevent the recruitment and activity of phagocytes and macrophages?
- kill cell - leucocidins - Staphs
- prevent opsonization - protein A (binds Fc portion of IgG) – Staphs
- block contact - capsules -meningococcus, Hib
How can intracellular pathogens enter macrophages
- promote own uptake (safe)- CR3; mannose lectin receptors
- prepares cell for invasion- Shigella – injects a protein to prevent activation of macrophages
- -ve P-L fusion- M. tuberculosis – inhibits phagolysosome fusion and acidification of endosome.
- escape P-L to cytoplasm - Listeria
- resist oxidative killing- produce catalases/peroxidases
Ways in which pathogens can avoid phagocytes
- Resists digestion and reactive oxygen species in phagolysosomes by producing enzymes such as Pods and catalase.
- Escape into the cytoplasm e.g Listeria
- Inhibit phagolysosome fusion maintains early endosome and blocks acidification e.g mycobacteria
- Control antigen presentation – stops cytotoxic t-cell or Po activation
- Directs phagocytosis via specific receptors
- Actin rearrangement so no engulfment
- Type 3 secretions system so it prepares the cell
Describe the production of Fc receptors by microbes
Microbes binds the Fc receptor so the antibody binds the wrong way round e.g Staphs, Streps, Herpes, VZV, CMV
How do intracellular pathogens and viruses conceal themselves?
Concealment of antigen
• hide inside cells
• privileged sites
• block MHC antigen presentation - Herpes -ve TAP protein
• - surface uptake of host molecules e.g. CMV and beta2microglobulin
Immunosuppression - e.g. decrease MHC, decrease receptors, apoptosis, cytokine switch IgA proteases
Antigenic variation
Persistence/latency/reactivation
Describe the mechanism of Streptococcus pneumoniae
On image
What can VIRUSES DO TO EVADE THE IMMUNE SYSTEM?
- Latency - VZV, herpes simplex
- antigenic presentation by binding to TAP - inhibits peptide transfer to MHC - Herpes simplex
- MCH expression - Cytomegalovirus (CMV)
- Mutation of epitopes B cells - neutralisation escape T cells - CD8+ escape mutants of HIV
Define Antigenic Diversity/ polymorphisms
genetically stable and alternative forms of antigens in a population of microbes
e.g. serotypes of Strep.pneumoniae
