IL-32 is a host protective cytokine against Mycobacterium tuberculosis in differentiated THP-1 human macrophages.
Macrophages provide a first line of defense against Mycobacterium tuberculosis. However, in instances where macrophage activation for killing is suboptimal, M. tuberculosis is capable of surviving intracellularly. IL-32 is a recently described cytokine induced by M. tuberculosis in a variety of cell types including human monocytes and macrophages. In this study, we investigated the biological significance of IL-32 in an in vitro model of M. tuberculosis infection in differentiated THP-1 human macrophages in which IL-32 expression was silenced using stable expression of short hairpin RNA (shRNA). Inhibition of endogenous IL-32 production in THP-1 cells that express one of three distinct shRNA-IL-32 constructs significantly decreased M. tuberculosis induction of TNF-alpha by approximately 60%, IL-1beta by 30-60%, and IL-8 by 40-50% and concomitantly increased the number of cell-associated M. tuberculosis bacteria compared with THP-1 cells stably expressing a scrambled shRNA. In THP-1 cells infected with M. tuberculosis and stimulated with rIL-32, a greater level of apoptosis was observed compared with that with M. tuberculosis infection alone. Obversely, there was significant abrogation of apoptosis induced by M. tuberculosis and a concomitant decrease in caspase-3 activation in cells depleted of endogenous IL-32. rIL-32gamma significantly reduced the number of viable intracellular M. tuberculosis bacteria, which was modestly but significantly abrogated with a caspase-3 inhibitor. We conclude that IL-32 plays a host defense role against M. tuberculosis in differentiated THP-1 human macrophages.
Bai
Xiyuan
X
Division of Pulmonary Sciences and Critical Care Medicine, University of Colorado Denver at Anschutz Medical Center, Denver, CO 80045, USA.
Kim
Soo-Hyun
SH
Azam
Tania
T
McGibney
Mischa T
MT
Huang
Hua
H
Dinarello
Charles A
CA
Chan
Edward D
ED
D017209:Apoptosis / Q000276:immunology; D015153:Blotting, Western; D002454:Cell Differentiation / Q000276:immunology; D002460:Cell Line; D016207:Cytokines / Q000276:immunology; D015870:Gene Expression; D006801:Humans; D020287:In Situ Nick-End Labeling; D007378:Interleukins / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology*; D009169:Mycobacterium tuberculosis / Q000276:immunology; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014376:Tuberculosis / Q000276:immunology*
D016207:Cytokines; C496971:IL32 protein, human; D007378:Interleukins; D034741:RNA, Small Interfering