Full Spectrum of LPS Activation in Alveolar Macrophages of Healthy Volunteers by Whole Transcriptomic Profiling

Despite recent advances in understanding macrophage activation, little is known regardinghow human alveolar macrophages in health calibrate its transcriptional response to canonicalTLR4 activation. In this study, we examined the full spectrum of LPS activation and determinedwhether the transcriptomic profile of human alveolar macrophages is distinguished bya TIR-domain-containing adapter-inducing interferon-ß (TRIF)-dominant type I interferon signature.Bronchoalveolar lavage macrophages were obtained from healthy volunteers, stimulatedin the presence or absence of ultrapure LPS in vitro, and whole transcriptomic profilingwas performed by RNA sequencing (RNA-Seq). LPS induced a robust type I interferon transcriptionalresponse and Ingenuity Pathway Analysis predicted interferon regulatory factor(IRF)7 as the top upstream regulator of 89 known gene targets. Ubiquitin-specific peptidase(USP)-18, a negative regulator of interferon a/ß responses, was among the top up-regulatedgenes in addition to IL10 and USP41, a novel gene with no known biological function but withhigh sequence homology to USP18.We determined whether IRF-7 and USP-18 can influencedownstream macrophage effector cytokine production such as IL-10.We show thatIRF-7 siRNA knockdown enhanced LPS-induced IL-10 production in human monocytederivedmacrophages, and USP-18 overexpression attenuated LPS-induced production ofIL-10 in RAW264.7 cells. Quantitative PCR confirmed upregulation of USP18, USP41, IL10,and IRF7. An independent cohort confirmed LPS induction of USP41 and IL10 genes. Theseresults suggest that IRF-7 and predicted downstream target USP18, both elements of a typeI interferon gene signature identified by RNA-Seq, may serve to fine-tune early cytokineresponse by calibrating IL-10 production in human alveolar macrophages.

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