Molecular mechanisms underlying the synergistic induction of CXCL10 by LPS and IFN‐γ in human neutrophils

Abstract

The CXCL10 chemokine is a critical chemoattractant for the recruitment of activated Th1 and NK cells into inflammatory sites. CXCL10 is typically produced by myeloid cells in response to IFN-c, as well as by neutrophils, though the latter require a costimulation with IFN-c and LPS. In this study, we investigated the molecular mechanism(s) whereby IFN-c and TLR4 ligation synergize to induce CXCL10 expression in neutrophils. By primary transcript real-time PCR analysis, we demonstrate that the CXCL10 gene is transcriptionally induced by the LPS plus IFN-c combination in neutrophils, consistent with previous studies showing that increased CXCL10 gene expression does not reflect enhanced mRNA stability. The IFN-c-induced STAT1 activation and the lipopolysaccharide (LPS)-induced NF-jB activation were not enhanced if neutrophils were exposed to both stimuli, whereas both transcription factors were activated by IFN-c or LPS in monocytes. Finally, pharmacological inhibitors of NF-jB demonstrated its role in the induction of CXCL10 expression by LPS plus IFN-c in neutrophils, and by LPS or IFN-c in monocytes. Together, these results suggest that in neutrophils, the synergy observed between LPS and IFN-c toward CXCL10 gene expression likely reflects the cooperative induction of the NF-jB and STAT1 transcription factors by LPS and IFN-c, respectively. IntroductionCXCL10/IFN-c-inducible protein 10 (IP-10) is a critical component of several immune responses, acting notably as a chemoattractant for activated NK and Th1 cells into sites of inflammation. CXCL10 mediates its various activities by binding to CXCR3 expressed on activated Th1 and NK cells [1], and influences the behavior of nonimmune cells that express a CXCR3. For instance, it inhibits endothelial cell proliferation through interfering with the function of receptors for the growth factors, basic fibroblast growth factor and vascular endothelial growth factor, resulting in the inhibition of angiogenesis [2].Neutrophils are cells of the innate immune system that play an essential role in antimicrobial defense via the release of numerous toxic mediators [3]. In addition, extensive research has now clearly established that the release of chemokines and cytokines constitutes yet another key contribution of neutrophils to innate immunity (reviewed in reference [4]). Among the chemokines produced by neutrophils both in vitro and in vivo, CXCL10 stands out as being somewhat peculiar in terms of its induction characteristics, as originally shown by us [5,6] as well as by other groups [7][8][9]. Indeed, CXCL10 expression occurs in vitro only if However, the molecular bases of the particular inducibility of CXCL10 in human neutrophils have only been partially elucidated thus far. In this regard, we have recently clarified that the reason explaining the inability of LPS to induce CXCL10 mRNA expression in neutrophils reflects the fact that in this cell type, LPS is unable to mobilize the intracellular MyD88-independent pathway upon TLR4 binding [11]. As a result, LPS fails to...

IFN-β Expression Is Directly Activated in Human Neutrophils Transfected with Plasmid DNA and Is Further Increased via TLR-4–Mediated Signaling

“…This is also in line with other experimental systems in which the induction of IFN-b results from a cooperative action of two different signals (54,55). Similarly, the present data are consistent with previous findings demonstrating that human neutrophils often require stimulation by two concurrent, but different, stimulatory pathways to optimally express a given gene [e.g., IFN-g plus LPS for CXCL10 (56) and IL-12 (57) expression or IL-10 plus LPS for IL-1ra (22) expression]. Curiously, LPS was unable to further upregulate the levels of IFN-b and CXCL10 transcripts in poly(I:C)-transfected neutrophils.…”

Decorin Potentiates Interferon-γ Activity in a Model of Allergic Inflammation

“…Proteoglycans can influence not only the stability but also potentiate signaling events. There are two major signaling pathways induced by IFN-␥, NF-B, and STAT-1 (64). In contrast to the role of decorin in septic inflammation (20), NF-B signaling is not affected in our model.…”

β2microglobulin mRNA expression levels are prognostic for lymph node metastasis in colorectal cancer patients

“…Despite the known biological properties of B2M, this gene has been inadvertently used as an internal reference control in studies involving IFN signalling (Einav et al, 2005;Tamassia et al, 2007), as well as real-time PCR studies of colon cancer prognosis (Takeuchi et al, 2003). Interestingly, in the study performed by Takeuchi et al, the investigators examined 36 tumours and observed that the mRNA copy numbers of B2M in T3/T4 cases (mean 1.78 Â 10 5 copies) had a tendency to be lower than that in T1/T2 cases (mean 4.44 Â 10 5 copies; P ¼ 0.16), but were not highly correlated with another reference gene.…”