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Asthma comes in seven or eight forms
Looking at every cell
A pathologist could once cut open the lung of an asthmatic patient who died and see thickened airways under the microscope. Now researchers can go into the tissue, look at every single cell, and ask how the cells are wired together.
Asthma's many patterns
Some forms of asthma are full of cells called eosinophils, and others are full of neutrophils. Some people respond to inhalers and others do not. Some are chlorine sensitive and react at a pool, and some are cold sensitive. Each pattern is an archetype, a play the immune system runs.
Autoimmunity follows suit
Autoimmune conditions follow the same logic. A study underway looks across a range of autoimmunities for shared features, and psoriasis, lupus, and inflammatory bowel disease all show variations. In inflammatory bowel disease, a drug that blocks a cytokine called TNF works well for some patients, and other patients respond for a while and then stop. Why one drug works in one patient and not another is not understood, so doctors try one after another.
How do doctors tell asthma types apart?
Doctors and researchers sort asthma by what is happening in the airways. They count eosinophils and neutrophils in blood or in coughed-up sputum, and they measure the nitric oxide in exhaled breath, which rises with a certain kind of inflammation. Eosinophil-rich asthma is driven by signaling molecules such as IL-5, IL-4, and IL-13. Mepolizumab, approved in 2015, blocks IL-5 and works mainly in the eosinophil type.
Why can pool chlorine trigger asthma?
When chlorine meets sweat and urine in pool water, it forms irritating compounds called chloramines, which evaporate into the air above the water. Studies of swimmers and pool workers have linked exposure to these compounds with damage to the lining of the airways. The damaged lining becomes more reactive to later triggers. This type of airway reactivity is distinct from allergic asthma.
How does single-cell analysis reveal hidden cell types?
Single-cell RNA sequencing reads which genes are active in each individual cell rather than averaging a whole tissue. That lets researchers sort cells into types and states by their gene activity. In 2018, two groups used it on airway tissue and independently found a rare cell, the pulmonary ionocyte, that is rich in the CFTR protein mutated in cystic fibrosis. Cell types invisible under a microscope showed up as clusters in the data.
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