Immunity to fungal infection

Question 1

What are the different types of fungi?

Answer 1

Chytridiomycota- water adaptive fungi, don’t cause human infection.
Zygomycota (mucomycota)- bread molds, can cause devastating infections in diabetics.
Basidiomycota- mushrooms, not usually pathogenic in humans.
Ascomycota- most of the fungi encountered in clinical practice, e.g. Candida, Aspergillus.

Question 2

What is Aspergillus fumigatus?

Answer 2

Major mold pathogen, causes pulmonary and disseminated infections.
2000-3000 deaths per annum in the UK.
Spores- clonidia.
Can lead to aspergilloma in leukaemia patients.

Question 3

What is Cryptococcus neoformans?

Answer 3

Spores.
Major pathogen in HIV patients, causing ~500,000 cases of cryptococcal meningitis associated with HIV patients per annum globally.
Basidiomycota- not macroscopic fungal fruiting bodies, microscopic organism.
Cryptococcomas (lethal, enhancing masses) in the brain can be seen on MRI, cause 40% mortality with meningitis.

Question 4

What happens in Candida endophthalmitis?

Answer 4

Occlusion of retinal arteries associated with fungal candida colonies growing into retinal space, causing blindness if not treated.

Question 5

Give an overview of cellular immunity to fungal infection.

Answer 5

More broadly similar to bacteria than to viruses.
Most fungi encountered at mucosal surfaces.
At mucosal surfaces, macrophages and neutrophils play a crucial role.
Dendritic cells take up fungi and present antigens to T cells in regional lymph nodes, leading to adaptive T cell responses e.g. Th1, Th2, TReg, Th17 etc. depending on clinical situation and factors relating to fungus.
Opsonisation by pentraxin 3 and mannose-binding lectin.
Antibodies and complement also important.
Phagocytes are a critical first line of defence.
NK cells provide early interferon-gamma.
A failure of innate immunity leads to adaptive responses.
Antibodies important for e.g. cryptococcus.

Question 6

Describe the processes of fungal morphogenesis, virulence and immunity.

Answer 6

Fungi (eukaryotic) are able to undergo multicellular transformation from unicellular forms, may occur in host.
Th1 response to unicellular, Th2 response to multicellular.
More difficult for phagocytic mechanisms to kill multicellular organism- too large to be phagocytosed.
Candidal dimorphism (yeast/hyphal forms) allows tissue invasion.
Cryptococcus forms a capsule to evade phagocytosis.
Aspergillus species inhaled as conidia, invade tissues as hyphae.

Question 7

What is ‘Toll’ (in relation to fungi)?

Answer 7

Toll is an innate pattern recognition receptor in Drosophila (fruit fly) required for fungal immunity.

Question 8

What receptors are important in signalling pathways in innate recognition of fungi, and why?

Answer 8

Wide range.
Almost all of the toll receptors, and the C-type lectins, are important.
C-type lectins detect carbohydrates on the fungal cell wall, and in addition to their signalling capacity down to NF-kappa-B in the inflammasome, also have important phagocytic function- fungi and mycobacteria.
Other receptors are for scavenging or damage response classes involved in fungal innate sensing and clearance.

Question 9

What is the dectin 1?

Answer 9

Dectin 1 is a major fungal pattern recognition receptor (C-type leptin receptor).
Important for phagocytosis of candida in animal models.
Important for chronic mucocutaneous candidiasis- primary immunodeficiency of childhood resulting in chronic mucosal fungal infection, hypertrophy of mucosa, and fungal drug resistance.

Question 10

What is the significance of human dectin 1 deficiency in relation to mucocutaneous fungal infections?

Answer 10

Loss of function mutation: Mendelian susceptibility to Candida albicans (chronic mucocutaneous candidiasis).
Impaired macrophage interleukin-6 production in response to C. albicans (lack of innate signalling responses to candida).
Homozygous mutation = reduced inflammatory response via IL-6 in macrophages, impaired macrophage binding/uptake of C. albicans.

Question 11

What is CARD9, its importance, and the significance of CARD9 deficiency in relation to chronic mucocutaneous candidiasis?

Answer 11

CARD9 is an adaptor molecule downstream of C-type lectins.
Functional CARD9 is required for TNF-alpha production in response to beta-glucan stimulation.
Functional CARD9 is required for T cell Th17 differentiation in humans.
Mutation more clinically severe.
Patients susceptible to mucosal infection and invasive, including CNS fungal disease (95% mortality).
Mendelian basis for susceptibility to fungal disease.

Question 12

What mutations may confer increased susceptibility to fungal disease?

Answer 12

Mutations in Dectin-1, TLR4 and plasminogen.

Question 13

How can toll-like receptor mutations affect the risk of developing fungal infections?

Answer 13

TLR4 polymorphisms increase the risk of invasive aspergillosis in transplantation.
The TLR4 S4 loss of function mutation increases risk of aspergillosis.
TLR9 is actively recruited to Aspergillus fumigatus phagolysosomes.

Question 14

How can dectin 1 mutations affect the risk of developing fungal infections?

Answer 14

Dectin 1 mutations increase susceptibility to invasive aspergillosis in stem cell transplantation.

Question 15

How can plasminogen affect the risk of developing fungal infections?

Answer 15

Plasminogen alleles influence susceptibility to aspergillosis in mice.
Plasminogen directly binds Aspergillus fumigatus Conidia.
Plasminogen alleles influence susceptibility to aspergillosis in stem cell transplantation.

Question 16

What is the role of interferon gamma in fungal infection?

Answer 16

Interferon-gamma therapy enhances clearance of infection in invasive fungal infection

Question 17

What is adoptive immunotherapy?

Answer 17

Stem cell transplantation.
Take off donor or recipient stem cells.
Anti-fungal T cells can be isolated by stimulating with fungi and skimming off using antibody capture technologies for cells that respond to fungi with a Th1 response.
Expanded ex vivo with growth hormones and cytokines.
Given back to patient when infected with fungus.
Enables more efficient immunological control of fungal disease.

Question 18

How is gene therapy used in fungal infections?

Answer 18

Chronic granulomatous disorder patients are at high risk of aspergillosis.
CGD: mutations in NADPH oxidase- important for generation of reactive oxygen species in the phagosome, neutrophils and macrophages.
In that condition, at high risk of candida, staphylococcus and aspergillus.
Gene therapy can be used to restore gp91 function.
Gene therapy can be used to restore neutrophil NET function.

Question 19

Which main cells contribute to fungal immunity?

Answer 19

Macrophages and neutrophils.

Question 20

What cells are of primary importance in aspergillus immunity?

Answer 20

Neutrophils.

Question 21

Which cells modulate adaptive immune responses?

Answer 21

Dendritic cells.

Question 22

Which type of response augments host immunity to fungi?

Answer 22

Adaptive T cell interferon-gamma responses.

Question 23

Which therapies have emerging utility for the treatment of fungal infections?

Answer 23

Interferon gamma or adoptive T cell therapy.

Question 24

What can gene therapy be used for?

Answer 24

Primary immunodeficiencies.

Question 25

Where are fungal spores commonly found?

Answer 25

In the air.

Question 26

List fungal spores that can induce infection or allergy.

Answer 26

Aspergillus niger.
Cochliobolus sativus.
Varicellaria rhodocarpa.
Orchis masculata (seed).
Cordyceps pseudolloydii.
Ascobolus immersus.
Podospora fimiseda.
Alternaria alternata.
Daldinia concentrica.
Cladosporium herbarum.
Laccaria laccata.
Coprinus sterquillinus.
Diplocladiella alta.
Sphaerosoma echinulatum.
Ganoderma applanatum.

Question 27

What is the size of an aspergillus spore head?

Answer 27

Spores 3µm across (i.e. easily are drawn into the lungs).

Question 28

Describe the damage response framework of microbial pathogenesis.

Answer 28

Switching between allergy and infection.

Depending on weak or strong immune response, either get Infectious or exaggerated allergic disease leading to death.

Question 29

What is the taxonomic distribution of characterised allergens?

Answer 29

Plantae magnoliosida = 33%
Animalia arthropoda = 27%
Fungi = 16%
Plantae liliopsida = 11%
Animalia chordata = 9%
Plantae coniferopsida = 2%
Animalia nematia = 2%

Question 30

Discuss the pathophysiology of allergic bronchopulmonary aspergillosis (ABPA).

Answer 30

Associated with asthma
Allergy to aspergillus
Destruction of airways, leading to bronchiectasis (widening of airways).
Pooling of mucus, and associated infection.

Question 31

How can allergic bronchopulmonary aspergillosis (ABPA) be treated?

Answer 31

Glucocorticoids- shut down eosinophils and mast cells.
monoclonal antibodies against IL5 and IgE.
Triazoles.
Amptericin B.
Omalizumab.

Question 32

What are the radiological features of allergic bronchopulmonary aspergillosis (ABPA)?

Answer 32

Dilated bronchi with thick walls.
Ring or linear opacities.
Upper or central region predeliction.
Proximal bronchiectasis.
Lobar collapse due to mucous impaction.
Fibrotic scarring.

Question 33

Give 2 conditions that can predispose to ABPA.

Answer 33

Asthma.

Cystic fibrosis.

Question 34

What are the obligatory criteria for ABPA diagnosis?

Answer 34

Total baseline serum IgE > 1000 IU/ml.

Positive immediate hypersensitivity skin test or Aspergillus-specific IgE.

Question 35

What are the supportive criteria for ABPA diagnosis?

Answer 35

Eosinophilia >500 cells/µl.
Serum precipitating or IgG antibodies to.
Aspergillus fumigatus.
Consistent radiographic abnormalities.

Question 36

What is the management strategy for ABPA?

Answer 36

Corticosteroids.
Itraconazole for steroid sparing effect.
Benefit of itraconazole past 16 weeks unclear.
Reduction in circulating IgE, steroid dependency and improved PFT.
Itraconazole indicated if not responding to steroids or steroid-dependent.
Role of inhaled steroids and other antifungals less clear.
Recombinant IgE monoclonal antibodies (omalizumab) may be useful.

Question 37

What is aspergillus rhinosinusitis?

Answer 37

May be allergic or invasive.
Increasingly common.
Association with atopy and nasal polyposis.
Raised total IgE, skin test and aspergillus-specific RAST IgE (or sometimes IgG).
May also be caused by Bipolaris or Curvularia.
Obliterated sinuses with hypoattenuated mucosa and enhancing material on imaging.

Question 38

How is fungal sinusitis treated?

Answer 38

Oral corticosteroids.
Surgical removal of obstructing nasal tissue.
Systemic antifungal treatment has not been shown to be effective.
Topical therapies being investigated.

Question 39

How is fungal sensitisation diagnosed in patients with severe asthma?

Answer 39

Severe asthma.
Positive immediate skin test or in vitro specific IgE to >1 filamentous fungus.
Exclusion of allergic bronchopulmonary aspergillosis.
Controversial diagnosis due to concerns about generalised sensitisation.
Use of antifungals unclear.

Question 40

What is hypersensitivity pneumonitis?

Answer 40

Also known as extrinsic allergic alveolitis.
Allergic response requiring long-term allergen exposure.
As a consequence often occupational.
Cell-mediated delayed sensitivity reaction.
Allergen-specific precipitins usually present.