Immunotherapy

Immunotherapy (allergen-specific immunotherapy, AIT) is a medical treatment that gradually changes the immune response to a specific allergen. The goal is not to mask the symptoms (that is what antihistamines do) but to reduce the immune system's sensitivity to the allergen through long-term, controlled exposure. It is the only treatment that can potentially change the natural course of allergic disease.

The principle is similar to vaccination: the patient is given very small but gradually increasing doses of purified allergen. The immune system "learns" to react to that allergen with tolerance instead of inflammation. The mechanism involves a shift from an IgE-dominant response to IgG4 (blocking antibodies) and a rise in regulatory T cells that calm inflammation.

Two main forms of administration:

• SLIT (sublingual immunotherapy) - tablets or drops the patient places under the tongue every day at home. The first dose is taken under medical supervision, the rest at home.

• SCIT (subcutaneous immunotherapy) - injections into the subcutaneous tissue of the upper arm at an allergy clinic. The first year is usually once a week (the dose build-up phase), then once a month (the maintenance phase) over 3-5 years.

Immunotherapy is not for everyone. Typical candidates:

• Pronounced pollen symptoms that are not well controlled by antihistamines and nasal corticosteroids alone • Patients whose allergy significantly affects their quality of life • Patients whose allergy has specific, clearly defined main allergens (e.g. birch only or grasses only) - polyvalent allergies are harder for AIT • Children over 5 and adults (there is usually no upper limit, but older people are assessed individually because of comorbidities) • People ready for a 3-5-year commitment

Contraindications or caution:

• Severe, poorly controlled asthma • Active autoimmune or malignant disease • Beta-blockers (absolute for SCIT) • Pregnancy for STARTING therapy (it can be continued if started earlier) • ACE inhibitors (increased risk of side effects with SCIT)

A typical course of treatment:

1. Assessment (allergist) - full patient history, skin tests or specific IgE, ruling out contraindications (severe asthma, autoimmune diseases, serious heart problems, pregnancy for starting therapy).

2. Choosing the form - SLIT is simpler for the patient (at home, no injections) but is not available for all allergens. SCIT covers a broader range of allergens and is considered somewhat more effective for some pollen allergies.

3. Build-up phase - the dose is gradually increased over several weeks to months.

4. Maintenance phase - a stable dose over 3-5 years. The effect is usually noticeable in the second season of therapy.

5. Monitoring - regular check-ups with the allergist, with dose adjustment if side effects appear.

In Croatia, immunotherapy is available through the allergy clinics of the university hospitals (KBC Zagreb, Split, Rijeka, Osijek) and a number of private practices. SLIT preparations for grasses and birch are largely available through the HZZO (Croatian Health Insurance Fund) with an allergist's recommendation. SCIT preparations come as individual extracts or as standardised therapies, depending on the allergen and the patient.

How effective is immunotherapy?

Studies show a 60-80% reduction in symptoms and in the need for other medicines in patients who complete the full 3-5 years of treatment. The effect is usually lasting - many patients maintain tolerance for years after finishing therapy. The greatest effect is seen in monovalent pollen allergies (grasses, birch, ragweed) and in allergy to wasp/bee venom.

What is the difference between SLIT and SCIT in practice?

SLIT (sublingual): tablets/drops under the tongue at home, less invasive, no injections, but it requires daily discipline and is not available for all allergens. SCIT (subcutaneous): injections at the allergist's, takes longer per visit, but covers a broader range of allergens (including combinations). Effectiveness is comparable for pollen allergies.

Can side effects occur?

Yes, but they are mostly mild. SLIT: itching and swelling of the mouth after a dose (it disappears within 15-30 minutes), less often mild nausea or stomach discomfort. SCIT: local swelling at the injection site, very rarely a systemic reaction (hives, breathing difficulty, low blood pressure). That is why SCIT injections are given at the clinic, and the patient stays under observation for 30 minutes after a dose.

Can my allergy "grow out" on its own without immunotherapy?

Some childhood allergies (milk, eggs) have a high rate of spontaneous remission. Pollen allergies and dust-mite allergy usually do not settle on their own - they can even worsen over the years. Immunotherapy is the only proven way to deliberately change the natural course.

Do I need immunotherapy if antihistamines help?

It depends on how much they help. If antihistamines keep your symptoms under control and you have a good quality of life, AIT is not necessary. If you keep increasing the dose, combine several medicines, or have symptoms that affect your sleep, work or sport - talk to an allergist about AIT as a long-term investment.

Can I do immunotherapy for several allergens at the same time?

Yes, but with limitations. SCIT often combines several allergens in the same injection (e.g. grasses + birch). SLIT is usually monovalent - one therapy per allergen. Polyvalent allergies require a longer assessment process to determine which allergens are primary (causing symptoms) and which are secondary (sensitisation only, without clinical allergy).

• Antihistamines
• Allergy season

• Genetics and environment - why allergies are on the rise

• EAACI - Allergen Immunotherapy Guidelines
• WAO - Allergen-specific immunotherapy position paper