The mature cysteine protease from Dermatophgoides pteronyssinus, Der p 1, is a major house dust mite allergen. Its enzymatic activity has been shown to have pro-in¯am-matory e ects that could alsonegatively in¯uence e cacy of allergen-speci®c immunotherapy. The aimof this study was to express recombinant pro-Der p 1 (rpro-Der p 1) in the yeastPichia pastorisand to study itsmaturation.