Human mucus proteinase inhibitor (human MPI). Human seminal inhibitor I (HUSI-I), antileukoprotease (ALP), secretory leukocyte protease inhibitor (SLPI).

Human mucous secretions contain a proteinase inhibitor which is produced locally and inhibits, besides trypsin and chymotrypsin, granulocytic elastase and cathepsin G as well as mast cell chymase and tryptase. The various inhibitors isolated from different sources (bronchial mucus, parotid secretion, seminal plasma, cervical mucus, etc.) and named accordingly (bronchial mucus inhibitor, BMI; human seminal inhibitor I, HUSI-I; cervical mucus inhibitors, CUSI; antileukoprotease, ALP; secretory leukocyte protease inhibitor, SLPI) proved to be identical or derived from a mature inhibitory protein encoded by a single gene of the human genom. Therefore, this inhibitor should be named mucus proteinase inhibitor, MPI. Such a neutral terminus would help to avoid misleading interpretations of already published data and also of the biological role of this inhibitory protein because the MPI may serve several and different physiological functions.