Contribution of Kazal-Like Domains of the Serine Protease Inhibitor-1 from Toxoplasma gondii in Asthma Therapeutic Vaccination Effectiveness

Background: We have previously showed rTgPI-1 tolerogenic adjuvant properties in asthma treatment, turning it a promising candidate for allergen-specific immunotherapy. This therapy is an alternative treatment to control asthma that still presents several concerns related to its formulation. rTgPI-1 contains independent inhibitory domains able to inhibit trypsin and neutrophil elastase, both involved in asthma pathology. Objectives: In view of the need to design rational therapies, herein we investigated the contribution of the different inhibitory domains in rTgPI-1 therapeutic effectiveness. Methods: BALB/c mice were rendered allergic by intraperitoneal OVA-alum sensitization and airway challenged. Once the asthmatic phenotype was achieved, mice were intranasally treated with OVA combined with the full-length recombinant protein rTgPI-1 or its truncated versions, Nt (containing trypsin-inhibitory domains) or Ct (containing neutrophil elastase-inhibitory domains). Afterward, mice were aerosol re-challenged. Results: Asthmatic mice treated with the neutrophil elastase- or the trypsin-inhibitory domains separately failed to improve allergic lung inflammation. Only when all inhibitory domains were simultaneously administered, an improvement was achieved. Still, a better outcome was obtained when mice were treated with the full-length rTgPI-1. Conclusions: Adjuvant ability depends on the presence of all its inhibitory domains in a single entity, so it should be included in potential asthma treatment formulations as a full-length protein.