BMS3021 Lecture Notes - Lecture 20: Pyroptosis, Spasticity, Cytokine Storm
30 May 2018
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Week 8. Intracellular pathogens (Shigella),
Extracellular pathogens (Clostridium) and, Viral
pathogens
INTRACELLULAR PATHOGENS (SHIGELLA OR BACILLARY DYSENTERY)
Bacillary dysentery or Shigellosis
• Host response gives almost all the disease symptoms
• Adaptive immune system does not play a role in this disease
• Very prevalent disease, mainly in developing countries and children under 5 years
• One of the most lethal diseases, more than malaria
• Transmitted through faecal-oral route by personal contact, food and water (40% secondary
attack rate within households) – high transmission rate
• Bacterial factors and host response combine to produce severe diarrhoea, fever and, stomach
cramps 1-2 days after infection
• Illness usually resolves in 5-7 days
• Symptoms:
o Fever
o Violent abdominal cramps
o Rectal urgencies
o Bloody and mucopurulent stools (blood and puss)
• Self-limiting (15% case fatality in toxigenic strains) – has to be treated
• Supportive therapy and ciprofloxacin at first line treatment
• No vaccine available and multidrug resistance is appearing
- almost all are becoming resistant
• Shigella:
o Gram negative anaerobic, non-motile, enteric bacteria
o Not part of the commensal flora
o Infective dose = 100-1000 bacteria
o Intracellular pathogen
o S.dyseteriae 1 produces Shiga toxin (epidemic strains)
o 214kb virulence plasmid – AI includes genes for type III secretion system (TTSS or T3SS) –
structurally related to flagella
o Virulence functions triggered by temperature shift, low pH, low PO2 and high osmolarity
o Encodes protein into eukaryote cell through IpaB/IpaC pore in T3SS (needle like structure
that can inject protein effectors from bacterium into host)
o Induction of micropinocytosis
o Escape into cytoplasm
find more resources at oneclass.com
find more resources at oneclass.com
o Multiplication and actin based motility/invasion – uses host actin to propel itself across cell
membranes and invade neighbours
o Signalling through PAMP receptors (PRR)
• “higella’s ad host’s otriutio to pathogeesis:
“higella’s otriutio
Hosts contribution
o Mucous layer penetration (has no adhesins
but direct contact through T3SS – do’t
know how)
o Low efficiency binding to epithelial cells but
transcytosis through M cells (specialised
phagocytic cells that can transport material
through transcytosis)
o Metabolic adaptation to the extra- and
intracellular environments
o Induction of host inflammatory response
o Invasion plus inflammatory (plus toxin
production) leads to tissue destruction ->
mucosal abscesses and ulcers
o Production of pro-inflammatory cytokines
o Recruitment and activation of neutrophils
-kills friends and foes
o Massive inflammatory response
o Epithelial destruction by neutrophils
-facilitates further bacterial invasion
o Activation of reflexes for intestinal emptying
and vomiting
o Mucous layer penetration (has no adhesions but direct contact through T3SS – do’t ko
how)
o Low efficiency binding to epithelial cells but transcytosis through M cells (specialised
phagocytic cells that can transport material through transcytosis)
o Metabolic adaptation to the extra- and intracellular environments
o Induction of host inflammatory response
o Invasion plus inflammatory (plus toxin production) leads to tissue destruction -> mucosal
abscesses and ulcers
• Infection process:
o T3SS is triggered by environmental signals
o Injected effectors induce cellular uptake of bacteria and subversion of transcytosis in M
cells
o T3SS effectors lyse vacuolar membrane
o Actin based motility takes cells to intercellular junctions for spread
o T3SS effectors stabilise epithelia cells for a while – so it does’t die too soo efore it
can reproduce
o Accumulation of PAMPs and cell death induce immune cell activation
1. Needs to get through mucus layer
2. Contact M cells and binds through T3SS
3. T3SS injected and reorganise cytoskeleton of M cell -> gobble of bacterium -> in vesicel
and trancytosed to the basal lateral side of M cell where macrophage/DC is waiting (has
receptors that allows more efficient entering then spreads laterally) -> senses no longer
in M cell ad breaks open into cytosol
find more resources at oneclass.com
find more resources at oneclass.com
• Virulence factors:
IpaB
o Most important
o At the tip of T3SS
o Engagement of basolateral receptors
o Membrane pore formation
o Macrophage pyroptosis (inflammatory lysis)
o Invasion plasmid antigen - > involved in injection and breaking of vesicles
IcsA (VirG)
o Hijack machinery
o Localisation at the old cell pole
o Recruitment of N-WASP (nucleation of actin polymerisation) – synthesis of actin
-> attracts attention of whole cell but masked by IcsB
o Intra-intercellular spread
o Essential for hijacking and movement
o Concentrated at one pole of the cell
o Encoded by virulence plasmid
IcsB
o Protection from autophagy
o Delete this gene = no infection
VirA
o Concentrated on new pole
o Degradation of microtubules
o Able to remodel microtubules to signal for entry into neighbouring cells
• Actin based motility leaves a passage – actin is polymerised at one end of the pole (old pole) to
propel the bacteria forward
• Actin also triggers a host response:
o Triggers for autophagy – septin cages are assembled around bacteria to prevent cell to
cell spread
o TNF-a greatly stimulates it
o Bacterium has to be quick to move
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Almost all are becoming resistant: shigella, gram negative anaerobic, non-motile, enteric bacteria, not part of the commensal flora. Induction of micropinocytosis: escape into cytoplasm, multiplication and actin based motility/invasion uses host actin to propel itself across cell membranes and invade neighbours, signalling through pamp receptors (prr, higella"s a(cid:374)d host"s (cid:272)o(cid:374)tri(cid:271)utio(cid:374) to pathoge(cid:374)esis: Higella"s (cid:272)o(cid:374)tri(cid:271)utio(cid:374: mucous layer penetration (has no adhesins but direct contact through t3ss do(cid:374)"t know how, low efficiency binding to epithelial cells but transcytosis through m cells (specialised phagocytic cells that can transport material through transcytosis) Hosts contribution: production of pro-inflammatory cytokines, recruitment and activation of neutrophils. Kills friends and foes: massive inflammatory response, epithelial destruction by neutrophils. Facilitates further bacterial invasion: activation of reflexes for intestinal emptying, metabolic adaptation to the extra- and and vomiting intracellular environments. Invasion plus inflammatory (plus toxin production) leads to tissue destruction -> mucosal abscesses and ulcers. Infection process: t3ss is triggered by environmental signals.
