Pulmonary Fibrosis Flashcards
Name 5 cell types in the lungs and their functions
Goblet cells - secrete mucus
Ciliated cells - have cilia to waft mucus
Basal cells - type of stem cell, proliferate to replace lost tissue
Alveolar Type I cells - gas exchange
Alveolar Type II cells - secrete surfactant to reduce surface tension
What are the 4 steps of the breathing cycle?
Diaphragm contracts (flattens) External intercostals contract Diaphragm relaxes Internal intercostals contract (if forced exhalation)
Name 5 risk factors for IPF
Air pollution Workplace dust Smoking Respiratory viruses Genetic predispositions
Name 5 symptoms of IPF
Dyspnoea Dry cough Fever Weight loss Clubbing of fingers
What part of the lung does IPF affect?
The interstitium i.e. the tissue and space surrounding the alveolae
How is IPF diagnosed?
Look for symptoms
Respiratory crackles heard with stethoscope
Honeycombing pattern seen with HRCT
Lung function tests
Bronchoscopy to visualise airways
Lung biopsy
Analysis of BAL fluid to inspect cell count
How is the progression of IPF monitored?
Pulmonary function tests (spirometry) such as
-FVC
-DLco
-FEV1/FVC ratio
Oxyhaemoglobin saturation
6 minute walk test
Thoracic imaging with HRCT, X-ray or lung biopsy
What is FVC?
Forced Vital Capacity
Maximum possible breath
Tidal volume + Inspiratory reserve volume + Expiratory reserve volume
What is DLco and what does it measure?
Diffusion capacity of the lung for CO. Measures extent to which oxygen passes from the alveoli to the blood
What is FEV1 and what should the and what should the FEV1/FVC ratio be in healthy people?
Forced expiratory volume 1 - how much air you can forcefully breathe out in 1 second.
Ratio should be at least 80%
What is the general mechanism of the fibroproliferative response to lung injury?
- Epithelial cell injury
- Activation of extrinsic coagulation cascade
- Inflammation - release of ROS, cytokines and growth factors TGFbeta1 and PDGF
- Leukocyte infiltration
- Alveolar endothelial cell proliferation
- Fibroblast recruitment and proliferation
- Fibroblasts differentiation into myofibroblasts, generating collagen and extracellular matrix
- Alveolar walls thicken
How does the fibroproliferative response cause IPF?
Persistent lung injury repeatedly triggers the response. Alveolar walls get progressively thicker. Surface area for gas exchange reduces until the lungs cannot function
What is an exacerbation of IPF and what causes it?
Acute exacerbation is a sudden rapid decline in health. Often leads to death. Thought to be caused by viral infection
What methods can be used to detect viruses in the lungs of IPF patients?
Take blood sample, lung tissue biopsy or lung fluid sample with bronchoscopy
Use PCR/qPCR on liquid sample
Immunohistochemistry on tissue sample
Detection of viral IgG or IgM antibodies
Which viruses have been associated with acute exacerbations of IPF?
Herpes simplex virus
Epstein-Barr virus
Human herpes virus 7 and 8
Cytomegalovirus
What is the structure of the herpes virus?
dsDNA
Toroidal shape
Icosahedral capsid (20 faces)
Has a tegument - viral matrix between the capsid and envelope that is filled with proteins
Describe the latent life cycle of the herpes virus
- Infection of epithelial cells
- Enters sensory neuron, retrograde transport up axon
- Viral DNA remains latent in cell body. Remains episomal
- Reactivation of virus by UV light, stress, immunosuppression
- Anterograde transport back down axon
- Recurrent infection of epithelial cells
Describe the lytic life cycle of the herpes virus
- Infection of epithelial cells
- dsDNA transcribed into RNA and proteins
- Viral replication
- Cell lysis
Describe the general immune response to a viral infection
- Viral antigens engulfed by APC and expressed on MHC II
- Naive T cell proliferates into Th1 and Th2
- Th1 secretes interleukins and interferons to activate cytotoxic T cells
- Cytotoxic T cells kill host cells expressing the viral antigen on MHC I
- Th2 cells activate B cells
- B cells differentiate into plasma cells that secrete antibodies
In what ways can animal models be useful for studying diseases and drug development?
Can understand disease at cellular and mechanistic level
Target discovery and target validation
Uncover structure-activity relationships and PK/PD profile
Dose selection - allometrically scale up for humans
Test safety of a novel molecular entity
What are the characteristics of an ideal IPF animal model?
Mimic key pathological features such as fibroblast proliferation
Disease should be progressive and eventually fatal
Prone to acute exacerbations
Should have relatively low grade granulocytic inflammation
What is the most frequently used animal model of IPF and how is it made?
Bleomycin mouse
Chemotherapeutic treatment given intratracheally, with side effect of pulmonary fibrosis. After a few weeks the amount of lung collagen doubles. Can be seen using a microCT
How can the bleomycin model be used to mimic acute exacerbations of IPF?
Injection of the murine gammaherpes virus on day 14. Confirm infection by measuring expression of viral genes gB, M3 and DNApol.
What are some pros of general use of mice models for disease research?
Widely accessible Reproducible Easier to perform large scale trials Rodents share characteristics with humans, similar GI tracts and endocrine systems Rodent genome completely mapped Easy to genetically modify High throughput Can look at effects across multiple species
What are some cons of general use of animal models for disease research?
Cannot take into account human genetic predispositions
Can only test one element of the disorder at a time
Method used to create model not same as pathogenesis in humans
Metabolic/systemic difference to humans
Why have many of the compounds successfully tested on the bleomycin model not been successful in humans?
Bleomycin fibrosis is reversible, IPF is not
Bleomycin model lesions are bronchiolocentric rather than in the alveoli
Compounds were administered in early disease phase so may have been preventative rather than reversing the disease
Name 4 other possible animal models for IPF and how they are made
Transgenic models - viral vectors used to control gene expression e.g. cause overexpression of TGFbeta1
FITC administered intratracheally, destroys lung architecture
Single whole body dose of irradiation induces lung fibrosis
Exposure to silica mineral fibres leads to development of fibrotic nodules
What are the current treatments for IPF?
Steroids (not actually used anymore)
Palliative care
Self-care (stop smoking, flu vaccine)
Oxygen therapy to raise oxygen saturation
Pulmonary rehabilitation (breathing exercises, singing groups)
Lung transplant
What are some potential pharmaceutical treatments that may be used for IPF in the future?
Nintedanib - tyrosine kinase inhibitor
Pirfenidone - anti-inflammatory, anti-oxidant and anti-fibrotic
Ganciclovir - anti-viral therapy that inhibits thymidine kinase to prevent viral DNA replication
N-acetylcysteine - precursor to the antioxidant glutathione
What is Nintedanib and how does it work?
Small molecular tyrosine kinase inhibitor
Inhibits PDGF, VEGF and FGF receptors
Prevents fibroblast proliferation and differentiation into myofibroblasts
What are the steps of tissue repair?
- Haemostasis/Coagulation cascade
- Inflammation by neutrophils and monocytes
- Proliferation of epithelial cells, endothelial cells and fibroblasts
- Remodelling - fibroblasts differentiate into myofibroblasts to form scar tissue
What are the components of the extracellular matrix and their functions?
Collagen - tensile strength Elastin - elastic stretch and recoil Proteoglycans - contains water and growth factors Adhesive glycoproteins Integrins - adheres cells to matrix
What are some cons of the bleomycin model?
Fibrosis will not develop in all mice that the chemotherapy is administered to
The timeframe to create the model is long
Name 1 pro and 1 con of the transgenic model of IPF
Pro: Gene expression can be tightly controlled, useful for understanding fibrosis pathogenesis
Con: Viruses can promote vigorous immune responses and they are highly trophic for epithelial cells
Name 1 pro and 1 con of the FITC model of IPF
Pro: Can visualise and monitor the lung fibrosis using thoracic imaging
Con: Very expensive
