Allergen-Specific Immunotherapy (ASIT): A Disease-Modifying Option for Feline Atopic Syndrome

Feline asthma and allergic skin disease are part of the feline atopic syndrome (FAS) spectrum—conditions driven by hypersensitivity to environmental allergens such as house dust mites, pollens, and molds. These allergens trigger inflammatory responses that result in airway constriction, eosinophilic inflammation, and pruritic dermatitis.

Traditional management relies heavily on glucocorticoids and bronchodilators for symptomatic control. However, these therapies do not address the root cause of allergic sensitization.

Why Consider ASIT?

Allergen-Specific Immunotherapy (ASIT) is the only treatment that modifies the underlying allergic disease rather than simply suppressing inflammation. It works by gradually introducing small doses of the identified allergen(s), promoting immune tolerance over time.

Mechanism of Action

- Shifts the immune response from Th2 (allergic) toward Th1/regulatory balance
- Increases regulatory T-cell (Treg) activity and IL-10 production
- Reduces IgE levels while increasing protective IgG ('blocking antibodies')
- Leads to reduced airway inflammation and clinical desensitization

Evidence Supporting ASIT in Feline Asthma

The systematic review by Mueller et al. (2021) compiled over 70 studies on feline atopic syndrome treatments, identifying 11 reports of ASIT in cats. Key findings include:

- Naturally occurring asthma: 67% (8 of 12 cats) achieved complete remission, allowing discontinuation of corticosteroids; 33% showed partial improvement.
- Experimental asthma: Rush immunotherapy (RIT) reduced airway eosinophilia and inflammation (QOE 1; SOR A).
- Feline atopic dermatitis: 45–75% of cats improved significantly with ASIT—comparable to results seen in dogs.
- Safety: Adverse events were rare and mild, typically limited to transient local irritation.

Overall assessment:
- Efficacy: QOE 2; SOR B for naturally occurring asthma
- Safety: QOE 1; SOR A — excellent tolerability

Clinical Application

Ideal candidates for ASIT include cats:
- With confirmed or suspected allergic asthma or dermatitis
- Requiring long-term corticosteroids or showing poor control on inhaled therapy
- Whose owners are committed to long-term management

Implementation tips:
1. Identify allergens via intradermal testing or serum IgE testing.
2. Begin ASIT while maintaining control with steroids; taper medication gradually as signs improve.
3. Expect noticeable improvement in 3–6 months, with optimal results at 9–12 months.
4. Continue maintenance therapy long-term for sustained remission.

Comparative Perspective

ASIT’s efficacy in feline asthma mirrors results seen in canine atopic dermatitis and feline allergic dermatitis, highlighting its role as a cross-systemic, immune-modulating therapy that targets the core allergic mechanism, not just its symptoms.

Key Takeaways for Practitioners

Take-Home Message

Allergen-specific immunotherapy is a cornerstone in the long-term management of allergic cats. It offers durable benefits, reduces medication burden, and enhances overall quality of life. With strong evidence of safety and growing clinical success, ASIT should be considered a standard component of multimodal therapy for feline asthma and other manifestations of feline atopic syndrome.

Positioning ASIT Among Other Therapies

While ASIT offers the only disease-modifying approach for feline atopic syndrome, traditional therapies still play an important role in symptom management and induction of remission. Below is a comparison of key therapies reviewed in Mueller et al. (2021).

Clinical Integration:
- Use glucocorticoids or ciclosporin for immediate control.
- Start ASIT concurrently once allergen identification is complete.
- Gradually taper anti-inflammatory medication as ASIT begins to take effect (typically within 3–6 months).
- Maintain ASIT for long-term stability and relapse prevention.