C4 Flashcards
Strategy that pathogen use to survive & reproduce
- Surviving colonisations
- Defending against complement
- Avoiding phagocytosis
- Survival inside phagocytes
- Immune evasion
- Resistance to antibiotics
How pathogen survive colonisation
- Must multiply to colonise host
- Must compete with normal flora for nutrients & space
- IgA Abs against adhesion inhibit attachment of pathogens to mucosal surface & prevent subsequent infection
Strategy to survive colonisation
- Rapid turnover of pili
- Antigenic variation
- IgA protease that cleave antibody molecule
- Produce siderophore
Delivery of effector molecules to host cells
- Deliver certain molecules directly to host cell
- Eg: damage the cell, loss of microvilli, uptake bacterial cell
Explain complement
- Heat labile component of normal plasma that enhance opsonisation of bacteria & allow antibody kill bacteria
- Activity said to complement the antibacterial activity of antibody
Role of complement system
- Made up large number of distinct plasma protein that react with one another to opsonise pathogens
- Number of complement protein are over 30
Mechanism to avoid killing by complement proteins
- Lysis of foreign cell by complement membrane attack complex (MAC)
- Opsonisation
- Inflammation
Gram positive or Gram negative susceptible to MAC
Gram negative
Define serum resistant
Gram negative bacteria that avoid killing by complement protein
Some pathogen carry surface components such as
- Sialic acid that capture complement regulatory protein that cause inactivation of C3b alternate pathways of complement
- N. gonorrhoea
Mechanism to avoid phagocytosis
- Prevent encounters with phagocytes (macrophages & neutrophils)
- Avoiding recognition & attachment
- Fc receptor
Explain preventing encounter with phagocytes
- Avoid detection
- Killing phagocytic cell
- Include C5a peptidase to degrade C5a
- membrane damaging toxin
What structure that are use to avoid recognition & attachment
- Capsule: interfere alternative pathways of complement activation
- M protein: similar functions of capsule
Explain Fc receptor
- Protein found on surface of S.aureus (protein A) & S.pyogenes (Protein G)
- Stop opsonisation by antibody
Mechanism use to survive inside phagocytes
- Escape from phagosome
- Preventing phago-lysosome fusion
- Surviving within the phagolysosome
Mechanism of avoiding antibodies
- IgA protease: cleave IgA
- Antigenic variation: changes surface antigen
- Mimicking host molecules: cover themselves with molecule resembles normal molecules
Explain the mechanism of avoiding antiviral effects of interferons (immune evasion)
- Encode certain protein that shut down translation in host
- Alter enzymatic activities in cell
Explain the regulations of host cell death by virus (immune evasion)
- Kill the host cell after production large no of viral copies in order to spread to other cells
- Control immune surveillance to avoid premature death of their host
- Replicate rapidly induce apoptosis or programmed cell death of host to limit inflammatory response
Mechanism of immune evasion
- Produce dsRNA intermediate to induce apoptosis
- Inhibit process of apoptosis by controlling p53 - associated with tumor development
- Block antigen presentation by MHC class I
- Cell not display MHC killed by natural killer cell
Explain about antibodies & viruses (immune evasion)
- Directly transfer from one cell to its neighbours (Mareck disease virus)
- Remain intracellular by forcing all cellular neighbour to join commune called syncytium (HIV)
- Use antibody to enhance ability to infect cell (antibody mediated enhancement infection)
- Outpace body capacity by producing virus specific Abs by shifting antigen (psudospecies)
Virus damages to the host (immune evasion)
- Lysis of cell
- Damage due to inflammatory response & destruction by virus & cytotoxic T cell
- Activation of apoptosis in host
Explain immune evasion in fungi
- Cause lung diseases & granulomatous damage to lung
- Produce mycotoxins (A. flavus)
- Spores &fungal element cause hypersensitivity
- Dermatophytes cause superficial infection of hair, skin, nails
Explain immune evasion in eukaryotic parasites
- Live in intestinal tract or enter body via antrophod
- Use variety mechanism to avoid antibody
- Hide within cell (RBC) - not present antigen
Example of immune evasion by eukaryotic parasites
- P.vivax attach to Duffy blood group antigen
- Leishmania survive & multiply in macrophages
- African trypansome avoid antibody by routinely varying surface antigen
