Lecture 5 Flashcards
What are some examples of human immune defences?
Lysozymes in tears
What is the difference between innate and adaptive immunity?
Innate recognises generic molecules while adaptive is molecule specific
What does PAMP stand for?
Pathogen Associated Molecular Patterns
What is one way pathogens have reacted to the immune response to PAMPs?
Glycosylate or other chemical modifications to PAMP
What do some innate cells do involving PAMPs?
Constantly survey for them - non specific ‘sledge hammer’ approach
Which cells are involved in adaptive immunity?
T cells and B cells
What are four ways bacteria evade host defences?
Hide
modify or block defences
molecular mimicry
phase/antigenic variation
What is a huge barrier for pathogens to get through in the stomach?
Acidity - pH 2
What bacteria has evolved to survive the stomach and how?
Helicobacter pylori
Adjusts pH of microenvironment by hydrolysis of urea to ammonia using urease (activated by low pH)
What other bacteria use urease and why?
Proteus mirabilis and Klebsiella sp use as a nitrogen source - pH
What can the pH change caused by bacteria cause?
kidney stones
What is one role of the capsule?
Protects from phagocytosis by macrophages
What did Wangdi et al discover about S. Typhi?
Misguides the macrophage with chemical sensing so it can’t even see the bacteria
How do human neutrophils recognise self?
sialic acid
What bacterias changes themselves to avoid neutrophils and how? (2 bacteria)
Streptococci sialylates its capsule
Haemophilus influenzae sialylates LPS
What is antigenic variation?
Having variants of protein with different antigenicity
What is the advantage of antigenic variation?
When a surface protein is common the immune system gets better at detecting it - a change prevents this
What is phase variation?
Reversible change in LEVEL of expression of a protein
How is phase variation mostly done?
Either ON or OFF
Can be high-medium-low
How did Van der Woude show heterogeneous expression?
Induced virE gene in A. tumefaciens and showed at intermediate levels of inducer it is differentially expressed in the population
What is heterogeneous expression?
The difference between bacteria not attributed to anything (not phase variation and non heritable)
Give an example of what can cause heterogeneous expression
Number of RNA polymerases in cytoplasm
How does heterogeneous expression affect phase variation?
A very small number of cells will display the opposite phenotype
Which molecules do phase and antigenic variation affect?
flagella
outer membrane proteins
LPS
fimbriae
How does the mutation rate for the 2 variations compare to the normal mutation rate?
Much higher and reversible
What molecular mechanisms are involves in phase variation?
Site specific recombination
Short sequence repeats
DNA methylation state change
What molecular mechanisms and involved in Antigenic variation?
Site specific recombination
gene conversion
Why does relapsing fever relapse weekly?
Antigenic variation of surface lipoproteins of Borrelia hermsii
How does Borrelia hermsii perform antigenic variation?
Has expression plasmids and storage plasmids (with out promoters) that are recombined to create lots of different ‘coats’
How do short sequence repeats change length?
Mismatch repair system messes up because with repeats it is difficult to detect - creates loops and so shorter strands
What are some ways to change protein expression for phase variation?
Prevent activator from reaching polymerase
changing coding sequence to sequester protein
How does Vibrio cholerae use phase variation?
Changes gene affecting O antigen (LPS)
What gene does Vibrio cholerae change and what does that do?
manA
increases phage resistance but reduces colonisation of intestine
What does Neisseria change on it’s surface and what does it use to do this?
Type IV pilus
Phase and antigenic
How does Neisseria perform antigenic variation?
Uses gene conversion that is RecA dependent to move the expression locus
What genes are recombined to change the pilus?
pilS and pilE
How many different sequecnes can be made for a pilus?
2^11
How many genes do they think are controlled by phase variation in Neisseria?
33
Why does Neisseria have so many changeable elements?
In preparation for an antibody or pressure they haven’t encountered before
What other site specific recombination can be involved in phase variation?
Recombinase inverts gene using ‘inverted repeat left/right’
What does E.coli change by phase variation?
Type 1 fimbriae
What genes are involved in the PV of E.coli’s fimbriae?
2 site specific tyrosine recombinases: fimB and fimE
What is the difference between fimB and fimE?
FimE promotes lots of change to OFF while FimB is equal ratio.
So what controls the phenotype of fim?
Relative amount of recombinases
What are some examples of things that regulate the Fims?
LRP, sialic acid, temp, RcsB - biofilm master regulator
What did locking the Fim in OFF show?
It could not colonise and so fimbrium is a virulence factor
What did locking Fim in ON show?
There was no difference between it and WT showing there was no advantage to having it on all the time (phase variation is not a virulence factor)
What is DNA methylation also known as?
Epigenetic regulation
Why is it tough to find DNA methylation by genomics?
Methylation not shown in sequence
What bacteria use DNA methylation?
E.coli
Salmonella
What enzyme do bacteria use to methylate DNA and what does it do?
Dam (deoxyadenosine methylase)
methylates adenine in GATC sequences
Features of Dam
Processive - both hemi and unmethylated dna is substrate
always present: 100-300 molecules per cell
What is the difference between methylation in humans and E.coli?
Reversible in humans
E.coli reverse by degrading DNA and synthesising new unmethylated strands
How does the cell stop Dam from methylating?
Regulatory protein blocks it from binding
What does the Pap operon show?
You can have a stochastic switch but also have regulatory inputs on it as well
What does the Pap operon look like?
A promoter next to papB and onwards to genes, then a divergent promoter for papI on the other side sharing regulation.
2 regulation sites GATC-I AND GATC-II
How is Lrp involved?
Binds to both regulation sites.
When bound to I is a promoter.
When bound to II is a repressor.
What else do PapB and PapI do?
PapI assists Lrp binding to GATC-I
PapB assists papI expression
What other regulator is involved in the pap operon?
cAMP-Cap only binds and activates transcription when glucose is not present
What cross regulation can PapB perform?
Can block foc (F1C)
Can block Type 1 fimbriae (fim)
Inhibit flhD (flagellar motility (stick or swim))
Why does PapB inhibit so many things?
Very specific for adhering to kidney cells so must get rid of everything else
What do all fimbriae down regulate?
Motility
