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Blood, 5 March 2009, Vol. 113, No. 10, pp. 2324-2335. Prepublished online as a Blood First Edition Paper on December 22, 2008; DOI 10.1182/blood-2008-03-146720.
PHAGOCYTES, GRANULOCYTES, AND MYELOPOIESIS Differential requirement for the activation of the inflammasome for processing and release of IL-1β in monocytes and macrophages1 Division of Infectious Diseases, University of Colorado Health Sciences Center, Denver; 2 Department of Medicine, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands; 3 Nijmegen Institute for Infection, Inflammation and Immunity (N4i), Nijmegen, The Netherlands; 4 Department of Internal Medicine/Infectious Diseases and Pulmonary Medicine, Charité-Universitätsmedizin Berlin, Berlin, Germany; 5 Department of Rheumatology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands; 6 Department of Medicine, National Jewish Medical and Research Center, Denver, CO; and 7 Department of Experimental Oncology E (Cell Biology), Istituto Nazionale per la Ricerca sul Cancro, Genova, Italy
The processing of pro-interleukin-1β depends on activation of caspase-1. Controversy has arisen whether Toll-like receptor (TLR) ligands alone can activate caspase-1 for release of interleukin-1β (IL-1β). Here we demonstrate that human blood monocytes release processed IL-1β after a one-time stimulation with either TLR2 or TLR4 ligands, resulting from constitutively activated caspase-1 and release of endogenous adenosine triphosphate. The constitutive activation of caspase-1 depends on the inflammasome components, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and NALP3, but in monocytes caspase-1 activation is uncoupled from pathogen-associated molecular pattern recognition. In contrast, macrophages are unable to process and release IL-1β solely by TLR ligands and require a second adenosine triphosphate stimulation. We conclude that IL-1β production is differentially regulated in monocytes and macrophages, and this reflects their separate functions in host defense and inflammation.
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