A clear, reassuring guide for people living with ABPA, CPA, asthma, SAFS, or bronchiectasis

Treatments for aspergillosis-related conditions often involve steroids, and more recently, biologics.
Many patients understandably wonder:

• What do these medicines suppress?

• Do they affect my ability to fight infection?

• Why are biologics considered safer than long-term steroids?

• Which parts of my immune system stay strong?

This guide explains the full picture in simple terms.

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🧬 1. Understanding Your Immune System: The Three Layers

Your immune system has three major lines of defence.

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⭐ A. Barriers — the first line

These stop pathogens entering in the first place:

• Skin

• Mucus in airways

• Cilia sweeping mucus out

• Tears, saliva, stomach acid

• Healthy bacteria (microbiome)

👉 Biologics do NOT affect barriers.
👉 Steroids can weaken skin and airway lining if used long-term.

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⭐ B. Innate immunity — fast responders

These act within minutes or hours.

Key cells:

• Neutrophils → main killers of Aspergillus

• Macrophages → engulf spores

• Dendritic cells → show pathogens to T-cells

• NK cells → kill virus-infected cells

Sensors:

• Dectin-1 → recognises fungal walls

• TLRs

• Complement proteins

👉 Biologics do NOT weaken these.
👉 Steroids weaken several key functions, especially neutrophils and macrophages.

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⭐ C. Adaptive immunity — targeted, long-term defence

Slower but specialised.

T-cells:

• Th1 → fight bacteria/viruses

• Th17 → major antifungal fighters

• Th2 → allergic pathways (IgE, eosinophils)

• Tregs → calm inflammation

B-cells & antibodies:

• IgG / IgA / IgM → normal infection defence

• IgE → allergy and ABPA pathway

👉 Biologics only suppress Th2/IgE pathways.
👉 Steroids suppress many T-cell and B-cell functions, not just allergy.

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🎯 2. What Biologics Suppress (Targeted & Selective)

Biologics used in ABPA and difficult asthma (omalizumab, mepolizumab, benralizumab, dupilumab, tezepelumab) only turn down allergic inflammation, not infection-fighting immunity.

🔻 A. They suppress:

• IgE

• Eosinophils

• IL-4 / IL-5 / IL-13

• Type-2 allergic inflammation

• Mucus hypersecretion (IL-13)

• TSLP airway alarm signalling

🛡️ B. They do NOT suppress:

• Neutrophils

• Macrophages

• Th1 immunity

• Th17 antifungal pathways

• T-cell killing function

• Antibiotic/cell-mediated defences

• Complement

• Dectin-1 fungal recognition

This is why biologics do NOT increase fungal infection risk.

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🔥 3. What Oral Steroids Suppress (Broad & Non-Specific)

Oral steroids like prednisolone reduce inflammation everywhere — including places you need for infection defence.

❌ A. They suppress key immune cells

• Neutrophils → move slower, kill less effectively

• Macrophages → reduced pathogen killing

• T-cells → weaker antiviral/antifungal defence

• B-cells → reduced antibody production

❌ B. They suppress important cytokines

• IL-1, IL-2, IL-6

• TNF-α

• Interferons

• IL-12, IL-23 (Th1/Th17 pathways)

These are essential for fighting viruses, bacteria, and fungi.

❌ C. They weaken antigen presentation

Dendritic cells and macrophages become less effective at “showing” pathogens to T-cells.

❌ D. They weaken barriers

• Thinner skin

• Thinner airway lining

• Slower wound healing

This increases infection risk.

❌ E. They reduce eosinophils and IgE (similar to biologics)

But they do this alongside suppressing many healthy parts of your immune system.

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🛡️ 4. What Remains Intact on Each Treatment

✔ On biologics (strongest preserved immunity):

• Neutrophil antifungal killing

• Macrophage function

• Th1 & Th17 immunity

• Antibodies (IgG, IgA, IgM)

• Complement

• Mucus & cilia defences

• NK cell antiviral defence

• Fever & inflammation responses

⚠️ On steroids (weaker preserved immunity):

• Complement

• Some antibody production

• Basic barrier function (though thinner)

Many infection-fighting cells work less effectively.

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🫁 5. Why Biologics Are Safer Long-Term for ABPA/SAFS

Because biologics:

• target only a tiny portion of immunity

• do not increase fungal growth

• do not raise infection risk

• reduce inflammation without broad suppression

• help avoid long-term steroid complications

Steroids:

• increase infection risk

• can worsen fungal colonisation

• damage lung structure over time

• cause weight gain, bone thinning, adrenal issues

• must be used short-term only when essential

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🌈 6. Summary Table

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🌟 7. One-Sentence Takeaway

Biologics turn down the allergic part of immunity (IgE, IL-4, IL-5, IL-13, eosinophils), while steroids suppress many of the infection-fighting parts as well — which is why biologics are much safer long-term.

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