Lecture 13 - Life Cycle Of Sporozoites Flashcards
Where are sporozoites present?
They are present on mosquito salivary glands
Where to the sporozoites travel?
They travel to the liver and invade hepatocytes by binding to HS proteoglycans
What do sporozoites become?
Exocrythrocytic and multiply and burst from liver cells and go into the blood as merozoites
What happens when sporozoites enter the blood?
They mature, divide and rupture the cell and infect new erythrocytes
What are the symptoms of malaria?
The loss of RBCs as they are destroying RBCs
What type of cycle is the erythrocytes symptoms of malaria?
It is an asexual cycle
What do some merozoites differentiate into?
Gametocytes which enter the gut of the mosquito and fertilisation occurs producing a zygote
What does the zygote differentiate into?
An ookinete and crosses the midgut wall and sits extracellularly between the basal lamina and the midgut
What does the ookinete differentiate into?
Into a Oocyst and sporozoites develop inside it
Where do the sporozoites mature?
They mature and invade the hemocoel of the mosquito and then travel to the salivary glands
What happens when the sporozoites travel to the salivary glands?
The mosquito bites a new host and the cycle repeats
How do sporozoites bind when they reach the liver?
They bind via circumsprozoite protein (CSP) which is positively charged to Heparan sulphate proteoglycan on the hepatocyte cell surface
The liver heparan sulphate (HS) is ….
Highly sulphated - more than other cells
What is the interaction between CSP on HS with liver cell surface?
It is a charged:charged interaction
How do the sporozoites identify the liver HS?
Because it is highly sulphated
What are the different forms of HS?
Unsulphated form - GlcNac-1-4 iduronic acid and an over sulphated form - GlcNS6S-14IdoA2S-1-4 (which has 3 sulphates)
What of HS do the mosquitos recognise the most?
The over sulphated form
What is the other function of the liver?
To remove the glycoprotein reminence - circlulating glycoprotein complexes that are present in the blood
What binds to HS proteoglycan to take up the glycoprotein remanents?
ApoE binds to HS proteoglycan via its highly sulphated surface
What competes with ApoE?
CSP competes for the same binding site hijacking the system, if you have lots of remanents being taken up by the liver (ApoE) then the uptake of the parasite (CSP) will be low
What does the mosquito do when the mosquito lands on you?
It spits and makes a hole, they have an anticoagulant so the blood doesn’t clot when they suck it up
What is present in mosquitos?
Syndecan is presnet
What does CSP bind to?
It binds to salivary glands not other cells
How could you extract GAGs from the PGs of the mosquitoes?
By SDS which leads to beta elimination - chop the GAG of the protein core
What would you use to get a better analysis?
Chop up HS to look for the trisulphated bit - use heparin lyase
What was found in peak 6 - the trisulphated entity?
No difference between the whole mosquito, salivary glands m midgut and ovary
What does surface plasmon resonance allow?
It allows for measurements of interactions
What is the comparison between HS and CSP with porcine liver HS?
The binding of HS and CSP has a slow association and slow dissociation, in porcine it is very rapid, comes to a plateau and then dissociates slowly
What do plasmodium sporozoites use to target their organs in human and mosquito?
They used HS proteoglycans
What is the most abundant transcripts in mosquito salivary glands?
Syndecan
What was found that the mosquito contains?
Trisulphated disaccharide that binds to ApoE on liver cells
Why does the sporozoite bind to liver cells if there is the same amount of trisulphate in the midgut?
When looking at the levels of chondroitin sulphates there was a much lower level in the gut than in the salivary glands. Binding in the salivary glands may require both GAGs (HS and Cs), CPS has been showed to bind to Cs
What will future studies show?
SPR with HS on specific organs instead of the whole fly
What is a receptor essential for erythrocyte invasion by plasmodium?
Basigin
What is the major infective agent in malaria?
Plasmodium falciparum (Pf)
What does the merozoite have on its surface?
PfRh5 which has been shown to be essential for parasite growth so it is a good candidate as a ligand for a receptor on red blood cells
What does soluble Basigin do?
Reduces the invasion efficiency of CSP
Basigin =
An OK blood group antigen
What happens if you don’t express highly level of Basigin?
You have a better chance of avoiding the problems of malaria
What is Basigin also known as?
CD147
What id needed for binding?
Ig domains 1 and 2 not carbohydrates
What is a new treatment for malaria?
Naturalising antibodies instead of injections
What is a problem with neutralising antibodies?
They don’t last long in circulation so you have to modify them to increase their life time circulation
