Endotoxins

Question 1

what part of the gram negative bacteria is the endotoxin

Answer 1

the lipopolysaccharide (LPS)

Question 2

what are the 3 main components of LPS and what do they consist off

Answer 2

LIPID A.
–Phosphorylated glucosamines attached to long chain fatty acids. No. and type of fatty acid vary by species.
–Hydrophobic
POLYSACCHARIDE CORE
–Ketodeoxyoctanoic acid (KDO) and heptose.
–Relatively constant between species.
–Hydrophilic
O- SIDE CHAIN
–Repeat units of tri, tetra or pentasaccharide sugars.
–Highly variable between species
–Hydrophilic

Question 3

what are the characteristics of endotoxins(7 points )

Answer 3

• Endotoxin is lipopolysaccharide (LPS)
• Lipid A is the active component. — not immunogenic.
• O antigen is highly immunogenic and immune specific.
• Found only in gram negative bacteria.
• Heat stable
• Not converted to toxoids.
• Major initiator of the sepsis pathway.

Question 4

what is sepsis

Answer 4

Life threatening organ dysfunction caused by

a dysregulated host response to infection.

Question 5

sepsis is primarily driven by which immune response and what cells dot hey consist of

Answer 5

Sepsis primarily driven by the innate immune system response. 
• macrophages, 
• monocytes, 
• granulocytes, 
• natural killer cells 
• dendritic cells.

Question 6

what do the cells from innate immunity detect in sepsis and how is the detection mediated and what is the effect

Answer 6

These cells detect
• pathogen associated molecular patterns (PAMP’s) such as endotoxin,
• damage associated molecular patterns (DAMP’s) from
damaged host cells.

This detection mediated via
• cell membrane receptors toll-like receptors (TLR) and
C-type lectin receptors.
• cytosol receptors - NOD-Iike receptors, RIG-I-Iike receptors.

Effect
• Production of pro- inflammatory cytokines TNFa, IL-I,
IL-6
• via inflammasomes to produce IL-I) and IL-18 that cause rapid programmed cell death

Question 7

what is the process of detection of endotoxin by innate immunity

Answer 7

the lipid A part is detected by the protein MD2 which then complexes with TLR-4. this induces dimerization and trigger downstream signalling which leads to production of pro-inflammatory cytokines e.g. TNF-alpha

Question 8

7 effects of pro-inflammatory cytokines

Answer 8

1. Increase number, lifespan and activation state of innate immune cells.
2. Increase adhesion molecule and chemokine expression by endothelial cells.
3. Increase acute phase protein such as complement, fibrinogen and CRP.
4. Cause fever.
5. Causes neutrophils to release extra-cellular traps (NETS) made of DNA and antimicrobial proteins that forms a scaffold for platelet activation.
6. Cause release of microparticles by activated platelets
7. Increase tissue factor expression by blood monocytes

5+6+7 formation of a thrombus (immunothrombosis)—microbes trapped within this. which attracts and activate further leucocytes.

Question 9

what does the dysregulation in sepsis do

Answer 9

–Production of reactive oxygen species (ROS) —
Hydroxyl and nitric oxide — damages cellular
proteins, DNA and lipids and impairs
mitochondria.
–Complement activation (esp. C5a) — increase ROS,
granulocyte enzyme release, endothelial permeability and tissue factor expression.
–Widespread immunothrombosis leading to disseminated intravascular coagulation (DIC) with
impaired microvasculature function and organ
dysfunction.
–Mitochondrial damage leads to decreased
intracellular ATP and cells enter state of
hibernation — exacerbates organ dysfunction.

Question 10

how is sepsis resolved

Answer 10

–Anti-inflammatory IL- 10 produced early in process which Supresses production IL-6 and y-interferon and
Stimulates production of soluble TNF receptor and IL-I receptor antagonist
–Autophagy of PAMP’s and DAMP’s — removal
–Damaged cells — undergo apoptosis and engulfment by macrophages.

Question 11

Meningococcal Sepsis

Answer 11

• Caused by Neisseria meningitidis
• Gram negative diplococcus
• Serotypes W135
• Serotype A associated with large outbreaks in Sahel
region of Africa — Meningitis belt.
• Serotype B,C and W135 found in UK — declined since
introduction of MenC and now MenB vaccine.
• Can cause disease ranging from meningitis to life
threatening meningococcal sepsis.

Question 12

what 2 things make meningococcus so effective insepsis

Answer 12

• O-antigen is very short

- produce membrane blebs which protrusions of membrane which are secreted