eosinophilic inflammation

The immune system has different 'squads' for different jobs. Eosinophils are a type of white blood cell specialised for allergic and parasitic responses. When they flood into the airways and release their irritant contents, they drive a particular flavour of inflammation that is common in allergic asthma.

Eosinophilic inflammation is airway inflammation dominated by eosinophils, recruited largely by type-2 immune signals (cytokines such as IL-5, IL-4, and IL-13). Their granule proteins damage the airway lining, promote mucus, and sustain hyperresponsiveness. This pattern often responds well to corticosteroids, which suppress eosinophils, and it can be tracked using blood eosinophil counts or exhaled nitric oxide.

Recognising this 'eosinophilic phenotype' has practical value: people with high eosinophil-driven inflammation tend to respond to inhaled steroids and, in severe cases, to biologic drugs targeting IL-5 or IL-4/IL-13. Not all asthma is eosinophilic, however — some is neutrophilic or paucigranulocytic — and a subgroup of COPD patients also show eosinophilic inflammation, which can guide their steroid use.