C6- Cryptococcus Virulence Flashcards
Where can you find it (saprophytic)
Avian habitats in cities
Soil
Trees eg eucalytpus
How do they usually reproduce (not dimorphic yeast)
through yeast budding
What mating type are 95% of haploid yeast (clones through asexual budding just fine )
Mat alpha
Can they undergo sexual
Yes but don’t need to, some African populations of cn are mat-a so can sexually reproduce for filament abs basidium formation
Give 3 sources of infection
Eucalyptus trees, bird excrement, environmental amoeba (can engulf them)
Where can it access to after dislodging from alveoli in Immunocompromised where spores can proliferate and escape macrophage killing
Skin, eyes, bones and cns mainly and trapped in capillaries of body
What’s the diff between mat alpha and a which suggests mat locus is important for infection but don’t know why
Alpha is more virulent in mouse models
and preferentially penetrates cns bbb
Also If you look at exp of mat locus when macrophage engulfs, more exp jn mat alpha
Why and where is it a problem (although present everywhere)
In sub saharan Africa and south east Asia where there is no access to retroviral drugs for hiv
How many does it kill in sub Africa alone each year
1/2 million
Is it the most common cause of fungal meningitis
Yes
Can it be transmitted human to human
No have to inhale environmental spores
Where is the new gatti strain mixed with local killing healthy (c gatti is not opportunist can cause disease in healthy)
Vancouver island since 2002
What is the theory of evolution from amoeba in which suggested they contact cn commonly - suggested reason they have evolved these ‘virulence factors’
Acts as a phagocyte with enzymes to degrade it too in a vacuole
So potentially evolved mechanisms for our macrophage escape too
PLUS FEMEMBER THE MAC IN IMMUNOCOMPROMISED MAY NOT BE CAPABLE EG DUE TO LACK OF CD4 mediated activation via ifny
When is mat alpha induced
Inside macrophage
- Metal related metabolism
Virulence factors
Which enzyme requires dinickel and what does it do
Urease
Acts to convert urea to ammonia for n source and ph change (alkaline)
Why are bird nests good for ammonia
They have a lot of Uric acid
How does nh3 gas ammonia convert to soluble nh4 form which changes ph
Acquires proton from environment
Which other pathogen uses urease ph change for advantage
H pylori
Where does our high conc body urea come from
Liver production
Explain how ph can affect macrophage activation
Conversion from T1 type which uses l-arginine to produce NO via nos
Into tissue healing type which produces l-ornithine and urea instead of NO
Osterholzer 2009 study - urease and non protective DC and macrophages in lung
Escape mediated
When infected with ure1 wt mice showed a t2 response. What was this
T2 cytokines like il4 and il13 which are immunosuppressive
Pulmonary eosinophils
Arginase conversion of l-arginine
Which enzyme is upreg in t2 response in mice wt and imbalance seen with lower nos2
Arginase (l-arginine to l-ornithine/urea)
Ko of ure1 impacted/reduced immature pulmonary dc. What marker was thsi
Low cd80/b7
How do ph from urease also affect the cns potentially
Normally they are trapped in the capillary bed but gain access to cross bbb
From mouse urease mutants. They cannot access the brain
Hypothesised it causes tj disruption in capillary wall cells and allows penetration
- Iron metabolism
What mechanism do we use in inflammation with infection/chronic diseases to starve fungi from iron and explain anemia in eg cancers
Hepcidin exp through il6 in liver
Ub and proteasomal deg of fpn and blocks absorption in enterocytes
What special fe efflux pump on phagosome starves then even more
Nramp1
Which 3 things do cn with high affinity (low fe needed) to import iron as an adaptation - need these to survive under iron starvation because they are high affinity
Fre1 reductases converting it to fe2
Then fet3 oxidase converting it back and pairs with ftr1 iron transporter
Why is cu toxic (2 reasons)
High in Irving Williams series- high affinity can displace eg iron
Also a redox metal which can react with h202 from resp and form hydroxyl radicals causing dna damage
Give 2 enzyme examples of displacement killing then
Fumarases and aconitases in tca cycle
(Both have 4fe-s)
What has the macrophage adapted to pump cu into the phafolysosome
When phagosome forms, Atp7a which has cu from atox1 chaperone relocates from tgn to the phagolysosome and pumps cu in
What 2 cys rich proteins cu has high affinity for do cn have to cope with cu toxicity - cannot displace metals
Shown through mutant experiments important
Mt1/2
Which tf when bound to cu induced exp of mt1/2
Cuf1 (represses ctr1 exp under these conditions too to stop import)
Capsule
What is the capsule made of and when is it induced
Glucoronoxylomannan
Induced by low fe, serum and co2 (physiological co2)
What happens within macrophage
Induced capsule and also is shed for its escape
Interferes with phagocytosis
Is gxm common in aids
Yes
How does gxm link to complement
Potent activator of the alternative pathway
It gets opsonised and depletes c3b opsonin in aids patients and isn’t destroyed by macrophages from opsonisation
Which complication seen with crypto meningitis is seen due to the viscous polysach capsule
High intracranial pressure
Sue to lymphatic drainage disrupted
Why is melanin important for 2 reasons
Antioxidant
Scavenges free radicals (block macrophage killing)
And also for uv protection
It is produced by laccase, what does this use
Brain dipholic compounds like dopamine or epinephrine (explains why induced in cns)
4- titan cell formation
What are Titan cells (many characteristics)
Large cells of 100microm in diameter
Prevents phagocytosis due to size
Resistant to many stresses in lungs
Polyploid (64 copies of genome)
Rapidly produce many daughter cells
The mechanism is not understood
Which acute treatment taken for 2 weeks to get rid of cn in csf
AmpB
What % of hiv srill die with ampB treatment due to meningitis
43%
What combination therapy given before it gets to brain
AmpB, flucytosine together
Or triple therapy with fluconazole too
To clear sufficiently before maintenance phase
What maintenance drug used for 8 weeks to fully clear cn
Fluconazole (400g) then reduced after 8 weeks to 200g
What 2 type of pseudohyphal forms are there
Linked yeast cells
Hyphae with constrictions
What is it suggested in environment is importance of pseudohyphae
Nutrient and amoeba resistance
What’s the difference between mating and fruiting
‘Mating is formation of dikaryon then basidium (Or monokaryon)
Fruiting is producing monokaryon with same mat locus type eg alpha x alpha (homothallic mating) - endonuclease activation for spore mat locus recombination
Which strain of cryptococcus found to selffilament through unisexual fruiting
D (very uncommon to do this but can provide a survival advantage)
Why does fruiting explain why alpha is more common
More alpha x alpha mating
What happens at basidium stage
Meiosis and 4 products form 4 basidospore chains on top of basidium
Give some conditions when hyphal growth/ mating is preferred
Below 37c, darkness, N starvation
What in mouse models was found 37c is required for
Required for systemic infection (yeast is more virulent than filamented)
What did pseudohyphal injection into mouse cns do
Failed to kill them and eventually the fungi depleted showing yeast from is more virulent
Why is prophylactic fluconazole given
High csf penetration
What is intracranial pressure increase associated with in meningitis
Visual/hearing loss and strong headaches
What wbc count in csf extremely low in hiv allows persistence
20 cells/microlitre
Is there evidence yeast can stay dormant eg in lung granulomas and infect years later?
Yes
