What are bronchoalveolar lavage - BAL sample?
what is done?
what does the sample show?
Saline is inserted down the airways and then pulled back up again
Sample will show various cells + mediators + cytokines as a proportional sample of within a person
What is asthma?
Asthma is a chronic inflammatory and obstructive condition typically categorised by episodes of reversible airflow limitation and bronchial hyperresponsiveness, where the patient experiences difficulty breathing (dyspnoea)
2 components of asthma
inflammatory and airway dysfunction
Inflammatory component of asthma
An inflammatory/immune system component, in which the individual develops a hypersensitivity to a specific stimulus (typically an allergen such as pollen or house dust mites), causing an exaggerated inflammatory response upon subsequent exposures to that stimulus
airway dysfunction component
effect? what symptoms?
An airway component, where the allergen-induced inflammation release mediators that affect cellular function, produce limitations in tissue function (i.e. airflow), resulting in the generation of symptoms (dyspnoea, excess mucus, and cough
Asthma is different for everyone
The symptomology and pathophysiology (the physiological mechanism by which pathology is produced) can vary greatly between individuals.
Therefore in this unit we will be focusing on particular subset of asthma, namely allergic, Th2 and IgE-mediated asthma.
Asthmatic airway compared to healthy airway
3 effects in asthma airway?
Contraction of smooth muscle -> leads to obstrruction + constriction of airway lumen
Excess mucus secretion -> further obstruct airways
Oedema/swelling -> swells up the wall
Overall effect = Decreased Luminal area -> Increased airway resistance = Decreased airflow which relates to the symptoms
Long term symptom of asthma
how does body overcome resistance? effect of this?
Increased respiratory effort is exerted to pull air through resistance
However, the increased resistance makes it harder to overcome by pulling force which can lead to respiratory fatigue (long/chronic attack)
Respiratory muscles get tired and can’t keep exerting force to maintain the level of ventilation in the presence of obstruction
How does contraction of the airway smooth muscles lead to airway obstruction and increased airway resistance?
airway made up of individual smooth muscle cells so when allergen-induced degranulation leads to a contraction, each muscle cell will become smaller hence overall effect is
decreased luminal area = increased resistance and decreased airflow
How can you reverse symtoms in asthma patient?
what drug used?
These changes are reversible - when the inflammation subsides or a bronchodilator drug is administered, the pathology subsides and airway resistance returns to normal
Beta-2 agonist e.g. salbutamol (bronchodilator)
How do inflammatory mediators induce ASMC contraction?
bind to which receptors? effect after binding?
Inflammatory mediators such as cysLTs, ACh, PGs bind to G-protein coupled receptors (e.g. M3) which leads to a particualr intracellular signalling process depending on the couple protein leading to increased Ca2+ mobilisation and sensitivity hence Ca2+ enters from intracellular stores or externally to lead to a muscle contraction
How does Beta-2 adrenergic receptor activation induce ASMC relaxation?
what does it bind to? effect?
Salbutamol is a Beta-2 agonist so it will bind to the beta-2 adrenoreceptor which activates the Gs coupled protein pathway hence activating more adenylyl cyclase which will convert more ATP to cAMP which activates more Protein Kinase A which reduces Ca2+ mobilsation and sensitivity hence leading to muscle relaxation
Short-acting beta-2 agonists (SABAs)
Short-acting beta-2 agonists (SABAs) such as salbutamol are the first-line therapy in asthma and are administered when required as reliever therapy (e.g. when the patient experiences an asthma attack) by metered-dose inhaler.
Long-acting beta-2 agonists (LABAs)
adminstered when? why? with what? dosage?
Long-acting beta-2 agonists (LABAs) such as salmeterol or formoterol are used as an add-on, preventer treatment, in combination with inhaled corticosteroids (this is because there is evidence that the use of LABAs without corticosteroids increases the risk of sudden death) in metered-dose inhalers, with twice daily, continual dosing.
Long-acting muscarinic receptor antagonists - tiotropium
LAMAs are widely used to treat chronic bronchitis in COPD patients, and as an add-on, preventer therapy in asthma. They are dosed on a daily, continual basis via metered-dose inhalers.
The action of LAMAs on airway tone involves blocking acetylcholine receptors present on ASM cells. Acetylcholine is a mediator and neurotransmitter that binds to M3 (muscarinic) receptors expressed in the membrane of ASM cells and induces contraction.
Therefore blockade of this receptor reduces the level of contraction in situations where acetylcholine plays a prominent role in inducing ASM contraction.
For this reason they are less effective as bronchodilators in asthma therapy, where acetylcholine typically has a more minor role in ASM contraction.
Finally, LAMAs may also provide benefit in patients with obstructive airway diseases by reducing mucus secretion and inhibiting cough.
2 stages of allergic asthma
sensitisation + allergic response
what is Sensitisation
the immune system first encounters the allergen and develops an adaptive (antibody- and lymphocyte-mediated) immune response hence the immune system is primed and more sensitive
what is the allergic response
the allergen is subsequently re-encountered, triggering the adaptive response previous primed during sensitisation hence more anitbodies and immune cells are available
This generates an inflammatory response within the airways, producing symptoms.
Overview of the sensitisation response
what does allergen stimulate? wha does this release? what does the allergen encounter? what do these usually do?
what happens next and which cell is involved? in what environment does this take place?
what does this cell interact with? effect of this?
what circulates around the body and where do they bind?
what else is secreted and their effects? what do they release and what is the net effect pf this?
During sensitisation, the allergen is inhaled and enters the airway tissue. This by itself often stimulates parts of the innate immune system, such as the epithelium, to release pro-inflammatory signals. The allergen is them encountered by antigen presenting cells (APCs), such as dendritic cells and macrophages, which patrol tissues searching for foreign particles to present to the adaptive immune system.
After engulfing and processing the allergen, a fragment of the allergen (an antigen) is displayed externally so that when the APC encounters a naïve helper T cell (a lymphocyte that acts to regulate immune responses) with an appropriate T cell receptor (i.e. one that recognises the antigen fragment), the antigen with be presented to the T cell, activating it and enabling it to mature into a Th2 cell, depending on the cytokine environment( the relative levels of inflammatory mediators such as IL-4 and TNF-alpha).
The activated Th2 cell then interacts with a B cell to initiate class-switching (the class of Ig antibody the B cell produces), proliferation, and production of IgE antibodies that bind the antigen present in the original allergen.
The IgE antibodies produced then circulate and bind (via their heavy chain/Fc region) to IgE (FcεRI) receptors on granulocytes such as mast cells (immune cells involved responses to parasitic helminths infections, which contain granules containing pro-inflammatory mediators such as histamine, leukotrienes and prostaglandins). When IgE is bound to its receptor in this way, the light chain/Fab region is still displayed, enabling antigen binding.
During sensitisation, Th2 cells will also secrete ‘Th2 cytokines’ such as IL-4, IL-5 and IL-13, which act to modulate the immune system. IL-5 in particular promotes survival, proliferation and trafficking (e.g. to the airways) of eosinophils (another polymorphonuclear granulocyte with roles in parasite defence that is heavily implicated in asthma).
Overview of the allergic response
what recognises the antigens upon re-exposure? what is released and effect of this? (5 key effects)
what is the immediate effect of this?
histamine role in asthma?
what does the allergen induce further activation of? effect of this?
Upon subsequent re-exposures, the antigens within the allergen are recognised by IgE molecules bound to mast cells within the airways. Multiple IgE molecules are cross-linked by the allergen, triggering degranulation, where the granulocyte releases its contents of inflammatory mediators. These mediators (e.g. prostaglandins, leukotrienes, cytokines) then bind to receptors present on multiple cell types within the airway that induce pathological changes, such as contraction of airway smooth muscle cells, microvascular leak (oedema), stimulation of goblet cells (mucus secretion), and activation of eosinophils, another granulocyte within the airways, triggering further release of inflammatory mediators.
The immediate effect of this process is rapid bronchospasm and a sharp decrease in airflow (due to the increase in airway resistance brought about by these changes).
It should be noted at this point that in contrast to many allergies, histamine release from mast cells appears to play a very limited role in the pathophysiology of asthma. Whilst drugs which block histamine receptors (anti-histamines) are one of the primary treatments for allergies in general, they are ineffective at treating asthma.
At the same time as activing mast cell degranulation, the presence of allergen within the airways also induces further activation of Th2 cells, which often induces secondary pro-inflammatory changes several hours later, as Th2 cytokine release induces eosinophils trafficking to the airways, where they become activated and release further pro-inflammatory mediators. Th2 cells release IL-4, IL-5 and IL¬¬ 13, eosinophils release reactive oxygen species, leukotrienes and proteolytic enzymes. The net effects of this can be a second decrease in airway function and period of airway hyper-responsiveness (a period where the threshold of allergen exposure required to elicit further asthma attacks is greatly reduced).
Outline role of key immune cells and inflammatory mediators in allergic asthma - summary
roles and inflammatory mediatr produced for
Th2 cells? B cells? mast cells? eosinophils?
a) Cell type
b) Role in asthma pathophysiology
c) Inflammatory mediators produced
1A) Th2 cells
1B)During sensitisation = Induces B cells to produce allergen-specific IgE.
During inflammatory response = coordination of immune response via cytokine release
1C) IL-4, IL-5, IL-13
2a) B cells
2b) Antibody production
3a) Mast cells
3b) Allergen-induced degranulation – release of inflammatory mediators
3c) Leukotrienes, prostaglandins
4b) Chemokine-induced degranulation – release of inflammatory mediators
4c) Reactive oxygen species, proteolytic enzymes, leukotrienes
effect of glucocorticoids for asthma
Reduce asthmatic inflammation by modulating the function of multiple immune & structural cells
Inflammatory effect reduce number of eosinophil reduce cytokines from T-lymphocytes reduce number of mast cells reduce cytokines from macrophage reduce number of dendritic cells
Reduce cytokines mediators of epithelial cell
Reduce leak of endothelial cell
Increase B2 receptors on airway smooth muscle
Decrease Mucus secretion
How do glucocorticoids reduce asthmatic inflammation?
CS diffuses through membrane & binds intracellular GR
Drug-receptor complex translocates to the nucleus
Drug-receptor complex binds DNA affects transcription
Altered transcription of gene
Corticosteroids increase or decrease expression depending on the specific gene/protein (e.g. ↑anti-inflammatory genes, ↓pro-inflammatory genes)
Translation of gene into protein
Why is corticosteriod used in a regular basis?
Used in recurring basis to prevent symotoms occuring so won’t do anything for someone experiencing an asthma attack in the moment but will have an long term effect
Asthma is a complex & heterogeneous condition with multiple endotypes
why is there different pathologies?
Different sub-types hence pathology is varied between which subtype you have therefore is diagnosed on a particular clinical pattern -> it is a reversible airway constriction in particular stimulus
Beta-2 agonists and corticosteriods work in a very broad way BUT more selective drugs can be used for sub-types
Treating airway inflammation
Inflammation of the airways is prominent feature of various respiratory diseases and plays a key role in inducing pathological changes within the airway. Therefore the inflammatory process is an important target of drugs used to treat these diseases
However the particular nature of the inflammatory response involved may vary between different respiratory diseases. For example, the inflammation implicated in asthma and COPD involves different initiating factors (allergens vs. tobacco smoke), immune cells, tissue environments (protease-anti protease balance, level of oxidative stress), cytokines and inflammatory mediators.
Therefore the anti-inflammatory efficacy of a particular pharmacological treatment will also vary depending on its individual mechanism of action (i.e. if the targets with which the drugs interact to produce its therapeutic effect do not play a prominent role in the disease, the drug is unlikely to be effective). For example monoclonal antibodies targeting IgE will only be effective if IgE plays a prominent role in the individual patient’s pathology.
The mechanisms by which the inflammatory cascade can be inhibited vary between individual diseases, however potential targets are summaries in the diagram below. As many of these processes are mediated by cytokines and other chemical mediators, they are a popular target of recent drug development (e.g. monoclonal antibodies targeting IL-4 and Il-13 in asthma therapy)
recent research findings
Research over the last decade has highlighted the role the innate immune system and non-antibody-mediated inflammation in asthma.
Certain allergen molecules can damage structural cells (e.g. airway epithelial cells), via proteolytic enzyme activity. Similarly, epithelial cells also appear to display a sentinel function and are capable of detecting specific molecular patterns on microbial and non-microbial allergens via pattern recognition receptors. Activation of epithelial cells via these mechanisms generates local inflammation and the release of alarmins, epithelial-derived mediators (TSLP, IL-25, IL-33) that prime antigen presenting cells and trigger downstream inflammatory responses.
Type-2 innate lymphoid cells (ILC2) are another cell more recently identified as playing a role in asthma pathophysiology. ILC2s are similar to Th2 cells (in terms of their role in releasing cytokines and coordinating certain inflammatory responses) but lack lymphocyte surface markers and antigen-specific receptors (e.g. T cell receptors). ILC2s become activated by alarmins, triggering release of the type 2 cytokines IL-5 and IL-13.
The realisation of the important role of ILC2s in asthma pathology has led to the inflammation present in allergic asthma being renamed from ‘Th2 inflammation’ to ‘type-2 inflammation’.
what is chronic obstructive pulmonary disease?
what is copd usuallu associated with?
does resp function return if you stop smoking?
COPD = an umbrella term used for a mixture of chronic bronchitis and emphysema, and encompasses a long-term, progressive, and accelerated decline in respiratory function.
≈90% of COPD associated with long-term tobacco smoke exposure
≈30% of long term smokers develop COPD
Other factors = genetic (e.g. Alpha-1 antitrypsin deficiency) and environmental hazards (e.g. pollution)
respiratory function declines with age for everyone but only maginally
stopping smoking doesn’t return function back (just slows down the accelerationof decline)
Effects of tobacco smoke
what does exposure to tobacco smoke do? what can they inactivate?
long term effect?
why can tobacco smoke lead to infections?
The pathogenesis of inflammation and respiratory function decline in COPD.
Excessive and repeated exposure to tobacco smoke induces respiratory tissue damage, initiating an inflammatory response characterised by macrophages and neutrophils, which release proteolytic enzymes that degrade structural proteins.
Exposure to specific chemicals in tobacco smoke also inactivate antiprotease enzymes, further increasing protease burden within the lung, leading to further tissue damage.
Over the long term, this leads to tissue remodelling (irreversible changes in lung and airway structure) that reduce ventilation and gas exchange.
Finally, other protective/defensive pathways within the airways such as mucociliary clearance are impaired by the remodelling (e.g. due to loss of cilia and hypersecretion of mucus) rendering the respiratory system vulnerable to infections that lead to exacerbations, during which inflammation increases (in response to the infection) and respiratory function declines dramatically.
How does smoking reduce respiratory function and lead to COPD? (flow chart)
effect of tobacco smoke and how it leads to tissue damage in different ways?
long term effect?
tobacco smoke -> inhalation of noxious chemicals and reactive oxygen species -> tissue damage
tissue damage -> inflammatory response which attract immune cells (via IL-8 and TNF-a) -> macrophage + neutrophil activation and trafficking -> increase protease burden -> tissue damage
inhalation of noxious chemicals and reactive oxygen species -> antiprotease inactivation -> increased protease burden -> tissue damage
tissue damage -> impaired mucocilliary clearance -> increased respiratory infections -> local inflammaotry response -> activate macrophage + neutrophil
Long term -> tissue remodelling -> irrersible change as nothing is healed therefore increased damage and degradation leads to decreased respiratory function
what is it?
what is a consequence of inflammation? what is it due to?
how is chronic bronchitis similar and different to asthma?
what is the primary cause of dysfunction in chronic bronchitis? how is this different to asthma? how does this affect treatment?
Chronic bronchitis (long-term inflammation of the bronchi/airways) is characterised by chronic and excessive sputum production, coughing and airway obstruction. The coughing and mucus production is a consequence of inflammation (due to smoke exposure or infection) within the airway tissue, activating sensory neurons and stimulating mucus glands.
Similar to asthma, chronic bronchitis involves impaired airflow through the airways due to reduced airway lumen radius and increased airway resistance. However whilst these changes are typically reversible in asthma, the changes in chronic bronchitis are generally progressive and irreversible.
The primary cause of the dysfunction also differs: in chronic bronchitis airway lumen size is reduced by excessive mucus secretion, tissue swelling, and degradation of the overall airway structure (resulting in the airway simply collapsing entirely when placed under excessive pressure), rather than being primarily caused by airway smooth muscle contraction, as in asthma. This has implications for the efficacy of specific therapies, as treatments such as beta-2 agonist bronchodilators, which act by relaxing airway smooth muscle, are less effective in COPD than asthma for this reason (this is discussed further in subsequent sections).
Chronic bronchitis - short summary
3 effects of chronic bronchitis?
what causes chronic brinchitis? (4)
Damage to cilia
Mucus hypersecretion (↑ goblet cells +↑ mucus gland activation)
Inflamed, swollen airway tissue + oedema
Weakened airway structure (loss of elastin) & loss of patency (airway collapse during expiration due to lack of elatsicity hence more obstruction + harder to breathe)
Impaired mucociliary clearance = increased risk of infection = recurrent infection
Irritation of sensory neurons = cough
Decreased luminal area = increased airway resistance and airway obstruction
what is it?
what does it result in? (2) effects of this?
what leads to an increased chance of collapse?
emphysema describes pathological enlargement of alveolar airspaces due to destruction and degradation of lung tissue. This results in loss of structural fibres such as elastin (increasing compliance) as well as reduced surface area and damage to the pulmonary vasculature (decreasing gas exchange
Decreased surface area + perfusion = ↓ gas exchange
Loss of elastin fibres = ↑compliance, ↓recoil
The loss of elastin fibres mean that you need to compress the airways to expel air from lungs due to lack of recoil -> this with loss of patency means increased chance of collapse (harder compression can lead to collapse)
what consequences does the airspace enlargement have in emphysema?
It can damage vascualture hence worsen perfusion
It can degrade walls of alveoli so some of the walls of the alveoli merge together to become 1 big alveoli with reduced SA
how does chronic hypoventilation of alveoli increase demands on the heart?
what does the increased demands result in? (3)
what does this increase the risk of? who is this a common cause of death?
Chronic hypoventilation of alveoli results in prolonged and widespread hypoxic vasoconstriction. Constriction of the pulmonary vasculature increases vascular resistance, in turn increasing the force required to pump blood through the system and the pressure of blood within it (pulmonary hypertension). This requires the heart to work harder to maintain normal blood flow against increased resistance, resulting in right heart hypertrophy and worsening efficiency.
Eventually the heart becomes unable to cope with the increasing demands placed upon it, resulting in heart failure, increased venous pressure and right ventricular afterload. This also greatly increases the risk of cardiovascular events such as myocardial infarction, a common cause of death in COPD patients (note that prolonged exposure to tobacco smoke will have also have likely had a significant negative impact on cardiovascular health directly, exacerbating the problem further and increasing the potential risk of catastrophic failure).
‘cor pulmonale’ - summary
how does it lead to cor pulmonale?
how does it lead to a reduced quality of life?
Chronic alveolar hypoxia -> Hypoxic vasoconstriction = increased pulmonary vascular resistance -> Pulmonary hypertension -> Increased right ventricular afterload,→ RV hypertrophy -> Right heart failure (cor pulmonale)
Chronic alveolar hypoxia -> Hypoxaeima, Hypercapnia, Acidemia -> Decreased exercise tolerance, Fatigue, ↓quality of life
2 main effects?
lower LV output -> lower circulating volume -> activate raas system
rhf -> cor pulmonale
what is it and what does it result in?
infection of the lung parenchyma, resulting in inflammation and oedema
3 classification tools?
can be classified according to:
• The type of pathogen responsible for the infection (bacterial, viral, fungal)
• The specific tissue(s) that are affected, e.g. lobar (the intra-alveoar space), bronchial, and interstitial.
• Where the infection was acquired (e.g. in the community vs. in hospital)
Pathophysiology of pneumonia-induced acute lung injury
what must first happen?
where do the pathogens go?
what is activated? what is recruited and released?
Weakening of host defence (e.g. following viral infection, damage to epithelium, or immune suppression)
Colonisation of alveoli by pathogens
Activation of macrophages and cytokine release (IL-6, IL-8, TNF-α)
Recruitment of neutrophils into alveolar space, release of proteases & ROS
Injury to alveolus and surrounding structures
How does alveolar injury lead to impaired gas exchange + hypoxaemia?
what causes oedema and effect of this?
what causes hyaline membrane formation? effect of this?
By these mechanisms, pneumonia can lead to ‘acute lung injury’ (an extremely serious condition that can lead to acute respiratory distress syndrome and death due to acute respiratory failure).
The inflammatory signal and injury to the alveolar wall, basement membrane and capillary endothelium, enables excessive fluid to be drawn into alveoli and surrounding interstitial tissue. This causes oedema to occur and reduces the rate of gas exchange (due to increased diffusion distance).
Similarly, damage to the alveolar wall and the accumulation of dead cells and fibrinous waste causes hyaline membrane formation (this where membranes that are normally thin and selectively permeable become thick and relatively impermeable) further limiting gas exchange.
How does alveolar injury lead to impaired gas exchange + hypoxaemia? summary flow chart
2 different ways this leads to hypoaemia?
what leads to lung sound crackles?
Alveolar injury ↓ Deposition of dead cells & proteins in alveolar wall (“hyaline membrane” formation) ↓ Impaired gas exchange ↓ Hypoxaemia
Alveolar injury ↓ Disruption of endothelium and basement membrane disruption ↓ Fluid accumulates in alveoli and/or interstitium (leads to lung sound crackles + lung opacity on X-ray) ↓ Impaired gas exchange ↓ Hypoxaemia