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Journal of Immunology Research
Volume 2015, Article ID 507315, 6 pages
Research Article

The Ability of Secretory Leukocyte Protease Inhibitor to Inhibit Apoptosis in Monocytes Is Independent of Its Antiprotease Activity

1Respiratory Research Division, Department of Medicine, Education and Research Centre, Royal College of Surgeons in Ireland, Dublin 9, Ireland
2Centre for Infection and Immunity, School of Medicine, Dentistry and Biomedical Sciences, Health Sciences Building, Queen’s University Belfast, 97 Lisburn Road, Belfast BT9 7AE, UK

Received 17 March 2015; Revised 20 June 2015; Accepted 23 June 2015

Academic Editor: Selvan Senthamil

Copyright © 2015 Niamh McGarry et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Secretory Leukocyte Protease Inhibitor (SLPI) is a serine protease inhibitor produced by epithelial and myeloid cells with anti-inflammatory properties. Research has shown that SLPI exerts its anti-inflammatory activity by directly binding to NF-κB DNA binding sites and, in so doing, prevents binding and subsequent transcription of proinflammatory gene expression. In the current study, we demonstrate that SLPI can inhibit TNF-α-induced apoptosis in U937 cells and peripheral blood monocytes. Specifically, SLPI inhibits TNF-α-induced caspase-3 activation and DNA degradation associated with apoptosis. We go on to show that this ability of SLPI to inhibit apoptosis is not dependent on its antiprotease activity as antiprotease deficient variants of SLPI can also inhibit TNF-α-induced apoptosis. This reduction in monocyte apoptosis may preserve monocyte function during inflammation resolution and promote infection clearance at mucosal sites.