THE antigen CD10 (common acute lymphoblastic leukaemia antigen), which is the zinc metalloprotease, neutral endopeptidase 24.11 (also known as NEP or 'enkephalinase')1-7, is expressed by acute lymphoblastic leukaemias8,9, normal lymphoid progenitors10, mature polymorphonuclear leukocytes11 and certain non-haematopoietic cells12. CD10/NEP hydrolyses several naturally occurring peptides, including the endogenous opioid pentapeptides Met- and Leu-enkephalin6. In invertebrate organisms such as the mollusc Mytilus edulis, Met-enkephalin triggers inflammatory responses by inducing morphological changes, directed migration and aggregation of haemocytes13,14. We report here that a structure related to CD10/NEP is expressed by M. edulis haemocytes and that abrogation of CD10/NEP enzymatic activity reduces the amount of Met-enkephalin required for haemocyte activation by five orders of magnitude. Similar results are obtained with CD10+ human polymorphonuclear leukocytes, indicating that CD10/NEP related structures regulate enkephalin-mediated inflammatory responses in organisms whose ancestors diverged ∼500 million years ago15.
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