Background:  Interferon (IFN)‐α is a cytokine that possesses potent anti‐viral and immunoregulatory activities. We aimed to assess clinical and immunological effects of low‐dose IFN‐α in patients with severe corticosteroid‐resistant asthma with and without Churg–Strauss syndrome. There is currently no efficient pharmacological treatment available for this group of patients.

Methods:  We studied 10 patients with corticosteroid‐resistant asthma, in which 3×10⁶ IU/day IFN‐α were administrated in addition to the prednisone dose given already before introduction of the cytokine therapy. The prednisone dose was gradually reduced dependent on the clinical situation and used as a clinical readout to evaluate the efficacy of the cytokine therapy. To distinguish between IFN‐α‐ and prednisone‐mediated immunological changes, the corticosteroid dose was kept constant for at least 2 weeks upon introduction of the cytokine therapy in seven patients. The effects of treatment on clinical and immunological parameters were measured at 2–4 weeks and 5–10 months depending on the availability of the patient.

Results:  Interferon‐α treatment rapidly improved the clinical situation as assessed by lung function parameters and required prednisone dose. Important immunological changes included: decreased leukocyte numbers, increased relative numbers of CD4⁺ T cells, increased differentiation of T helper (Th)1 cells, and increased expression of interleukin (IL)‐10 in peripheral blood mononuclear cells.

Conclusion:  Interferon‐α treatment was associated with dramatic improvements in the condition of patients with corticosteroid‐resistant asthma with and without Churg–Strauss syndrome. Potential mechanisms of action include the establishment of a correct Th1/Th2 balance and the induction of the anti‐inflammatory IL‐10 gene.