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Last reviewed: 11 March 2026

Key points

Eosinophilic asthma is a form of severe asthma driven by inflammation involving eosinophils.
Eosinophils are white blood cells that normally help fight infection but can cause airway inflammation when overactive.
Biologic medicines are targeted antibody therapies designed to block specific immune pathways involved in asthma.
These treatments can significantly reduce asthma attacks and may allow reductions in steroid medication.
Biologics are usually prescribed in specialist severe asthma clinics when standard treatments are not sufficient.

What is eosinophilic asthma?
What are biologics?
Types of biologic medicines for asthma
Tezepelumab
Access to biologics in the UK
Common questions
When to seek medical advice
Author and review information
References

What is eosinophilic asthma?

Eosinophilic asthma (EA) is a form of severe asthma associated with high levels of a type of white blood cell called eosinophils.

Eosinophils are part of the immune system and normally help protect the body from infections and parasites. They release chemical substances that kill pathogens and help trigger inflammation so that other immune cells can reach the affected area.

In eosinophilic asthma, however, this system becomes overactive. Large numbers of eosinophils accumulate in the airways, leading to:

airway inflammation
swelling of the airway lining
excess mucus production
narrowing of the breathing tubes

This inflammation causes asthma symptoms such as:

wheezing
shortness of breath
chest tightness
persistent cough

Eosinophilic asthma is part of a broader group of conditions known as Type-2 (T2) inflammatory asthma, which involves immune signalling molecules such as interleukins and IgE.

Reducing eosinophil activity is therefore an important goal of treatment.

What are biologics?

Biologics are specialised medicines made using biological processes. Most biologics used in asthma are monoclonal antibodies — laboratory-produced proteins designed to block very specific targets in the immune system.

Unlike traditional asthma treatments such as corticosteroids, which affect many parts of the immune system, biologics are designed to target a specific pathway involved in inflammation.

Biologics are usually given by:

subcutaneous injection (under the skin)
intravenous infusion (in hospital for some medicines)

Because they are targeted treatments, biologics can:

reduce asthma exacerbations
improve lung function
reduce reliance on oral steroids
improve quality of life for people with severe asthma

Types of biologic medicines for asthma

Several biologic medicines are currently used to treat severe asthma.

Anti-IL-5 therapies

These medicines block a signalling protein called interleukin-5 (IL-5), which plays a key role in activating and maintaining eosinophils.

Examples include:

Mepolizumab
Reslizumab

By blocking IL-5, these drugs reduce the number of eosinophils in the bloodstream and lungs, leading to reduced inflammation.

Anti-IL-5 receptor therapy

Benralizumab works slightly differently. Instead of blocking IL-5 itself, it binds to the IL-5 receptor on eosinophils.

This attracts natural killer cells from the immune system, which then destroy the eosinophils. As a result, eosinophil levels may fall dramatically.

Anti-IgE therapy

Omalizumab targets an antibody called IgE, which plays a central role in allergic asthma.

IgE activates immune cells that release histamine and other inflammatory chemicals. These reactions can trigger asthma symptoms.

This pathway is particularly relevant for people with allergic asthma, including some patients with allergic bronchopulmonary aspergillosis (ABPA).

Anti-IL-4 / IL-13 therapy

Dupilumab blocks two important inflammatory signals: interleukin-4 (IL-4) and interleukin-13 (IL-13).

These signalling molecules drive several features of allergic inflammation including:

IgE production
airway inflammation
mucus production

Blocking these pathways can reduce asthma attacks and improve breathing.

Tezepelumab

Tezepelumab is a newer biologic therapy that works higher up in the inflammatory pathway.

It blocks a molecule called thymic stromal lymphopoietin (TSLP). TSLP acts as an early warning signal released by airway cells when they are irritated by allergens, viruses or pollutants.

Because TSLP sits at the start of several inflammatory pathways, blocking it can reduce both:

allergic asthma pathways
eosinophilic inflammation

Clinical trials have shown that tezepelumab can significantly reduce asthma exacerbations, including in some patients who do not have high eosinophil levels.

Access to biologics in the UK

In the UK, biologic medicines are usually prescribed through specialist severe asthma clinics.

Eligibility is determined using guidelines from the National Institute for Health and Care Excellence (NICE). These guidelines consider factors such as:

frequency of asthma attacks
blood eosinophil levels
IgE levels
previous response to steroid treatment
overall asthma severity

Patients must usually demonstrate that they are:

taking their current asthma medications correctly
using inhalers regularly
still experiencing severe symptoms despite treatment

Assessment is often carried out in specialist centres such as severe asthma clinics.

NICE guidance for biologic therapies:

Common questions

Do biologics cure asthma?

No. Biologics do not cure asthma, but they can significantly reduce symptoms and asthma attacks.

Can biologics replace steroids?

In some people biologics allow a reduction in oral steroid use. However, many patients still require inhaled steroid treatment.

Are biologics safe?

Biologics are generally well tolerated, but like all medicines they may have side effects. Doctors will monitor treatment carefully.

Are biologics relevant for aspergillosis?

Some biologics, particularly anti-IgE or anti-IL-5 therapies, may be used in patients with asthma complicated by fungal allergy or allergic bronchopulmonary aspergillosis.

When to seek medical advice

Speak to your respiratory specialist if:

your asthma remains poorly controlled despite treatment
you require frequent steroid courses
you experience repeated asthma attacks
your doctor has suggested referral to a severe asthma clinic

Biologic therapies are usually considered when standard treatments are no longer sufficient.

Author and review information

Author: Aspergillosis Website Editorial Team

Audience: Patients, carers, GPs and non-specialists