MIEM Flashcards
What do virulence factors promote?
→Colonisation and adhesion
→To establish infection
→Promote Tissue Damage
→Growth, Transmission e.g. toxins
What aspect of immunity have pathogens evolved to overcome or avoid?
→Natural defences - mucosal layers, skin,
→Innate immunity
→Adaptive Immunity
How do microbes evade the complement system through negative binding?
→coating with non-fixing IgA instead of IgG
→Capsule blocks C3b binding
→Capsule prevents C3b receptor access
→sIgA proteases
How do microbes evade the complement system through disruption of regulation?
→Factor H sequestration
→Factor H regulates complement
How do microbes evade the complement system through expelling MAC?
→C5a proteases , blebbing
How do microbes evade phagocytosis?
→kill cell - leucocidins
→prevent opsonisation
→protein A (binds Fc portion of IgG) - blocks ability of antibody to bind to Fc receptors
→capsules have PAMPs not recognized by phagocyte
How do intracellular pathogens evade killing?
→Promote own uptake (safe) - CR3; mannose lectin receptors
→Prevents reactive species- produce catalases/peroxidases
→Inhibit Phagosome-lysosome fusion
→ Escape Phagosome-lysosome to cytoplasm
→Dysregulation of apoptosis
Mechanisms that enable life inside macrophages
→Directs phagocytosis via CR3 – no reactive species
→Actin rearrangement - +ve engulfment
→Type 3 secretion systems – prepares cell- phagocytosed in a safe way
→Resists digestion and ROIs in PLs - SOD, catalase
→Escape into cytoplasm from lysosome
e.g. Listeria
→Inhibits PL fusion maintains early endosome
→ Blocks acidification e.g. mycobacteria
→Controls antigen presentation
Stops CTLs or P activation
What is protein A?
→mimics of Fc receptor which sequester antibodies in the wrong way
→Access to surface antigen by specific antibody blocked
What are the ways the microbe evade adaptive immunity?
→Concealment of antigen
→Immunosuppression
→Antigenic variation
→Persistence/latency/reactivation
What type of bacteria is Streptococcus?
→Gram positive
→Commensal of upper respiratory tract
What is the mechanism of Strep?
→Have capsules to avoid detection
What conditions does Strep cause?
→Pneumonia;
→Otitis media;
→meningitis
Describe pathogenic mechanisms of Strep
→aerosol →Colonisation of nasopharynx (adhesins; receptor NAc-hex-gal ) →Inhalation into lungs →By-passes defences: surfactants, pneumolysin →Reaches lung
What happens when Strep reaches the lungs?
→Escapes phagocytosis (capsules) →Inflammation -Lung damage (teichoic acids; pneumolysin) →Damage to endothelial cells (inflammation; pneumolysin)
How many serotypes of Strep?
→more than 80
→due to capsules
How do surfactants prevent bacteria evasion?
→prevent bacteria from reaching epithelial lining of the lung
→Facilitate expelling of bacteria through mucus
How do viruses evade adaptive immune reponse?
→Latency
→reduce antigenic presentation
→reduce MHC presentation
→Mutation of epitopes
How do viruses reduce antigenic presentation?
→by binding to TAP - inhibits peptide transfer to MHC
Example of virus which reduces MHC expression
→Cytomegalovirus (CMV)
How do mutations of epitopes help viruses evade adaptive respnse?
→B cells - neutralisation escape
→T cells - CD8+ escape mutants of HIV
What is phase variation?
→ON/OFF of an antigen at low frequency
→occurs - during course of infection in an individual host
→ during spread of microbe through a community
What can structures on viruses undergo to allow for persistence and infection?
→Phase variation
→Antigenic variation e.g. pilins (or both phase and antigenic)
What type of virus is influenza?
→RNA virus with envelope
Compare HA and NA on influenza
→HA=binding to the host receptor protein,
→NA gene= a receptor destroying enzyme, is involved in release of the virus from the host cell
How many types of HA?
→18
→Segmented –ve ssRNA genome
How many types of NA?
→11
→8 segments, at least 10 genes
What is antigenic drift?
→mutation + selection
→Changes and mutations along with poor RNA polymerase without proofreading means more changes in HA and NA
→epidemics
What is antigenic shift?
→gene reassortment
→When two diff viruses coexist in host they can exchange and recombine gene segments making new strains of virus
→pandemics
