Regulated production of the interferon‐γ‐inducible protein−10 (IP‐10) chemokine by human neutrophils

Abstract

Interferon-gamma (IFN-gamma)-inducible protein-10 (IP-10), a member of the C-X-C sub-family of chemokines, is known to be produced by monocytes, lymphocytes, keratinocytes and endothelial cells in response to IFN-gamma. Here, we show that human polymorphonuclear neutrophils (PMN) also have the ability to produce IP-10. IFN-gamma alone had a modest effect on IP-10 mRNA accumulation, whereas tumor necrosis factor-alpha (TNF-alpha), yeast particles opsonized with IgG (Y-IgG), lipopolysaccharide (LPS), and formyl-methionyl-leucyl-phenylalanine (fMLP) all failed to up-regulate IP-10 gene expression. However, stimulation of neutrophils with IFN-gamma in combination with either TNF-alpha or LPS (but not with Y-IgG or fMLP) resulted in a considerable induction of IP-10 mRNA transcripts, as well as in the extracellular release of the protein. In contrast, the best inducer of IP-10 release from peripheral blood mononuclear cells was IFN-gamma alone. Furthermore, mRNA stabilization analyses demonstrated that IP-10 mRNA isolated from PMN stimulated with IFN-gamma only, or with IFN-gamma plus either TNF-alpha or LPS, had similar half-lives. Finally, we found that interleukin-10, a known inhibitor of chemokine production in PMN, moderately suppressed the extracellular production of IP-10 in neutrophils stimulated with IFN-gamma plus either LPS or TNF-alpha. Since IP-10 is a potent chemoattractant for activated T lymphocytes, the ability of neutrophils to produce IP-10 might contribute to the evolution and progression of the inflammatory response.

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

“…Further investigation shown herein (Fig. 1), supported by additional time-course and dose-response experiments (not shown), confirmed that the effects of Ultrapure LPS (used with or without IFN-c) on the release of CXCL10, TNF-a and IL-1ra by neutrophils were similar to those exerted not only by the original batch of LPS (from Escherichia coli, 0111:B4 strain) from which it was ultrapurified, but also by the same LPS preparations (from E. coli, 026:B6 strain) used in our previous publications [5,6]. Accordingly, real-time PCR studies confirmed that the induction of CXCL10 ( Fig.…”

“…6). Such a scenario would also be consistent with the known ability of TNF-a to synergize with IFN-c in inducing CXCL10 mRNA in neutrophils [5,6] and other cell types [15], as well as with the known ability of TNF-a to activate NF-jB in neutrophils [19]. It is also consistent with the identification of the mechanism underlying the marked synergy between LPS and IFN-c on CXCL9 mRNA expression in mouse macrophages, which was shown to be the result The synergy was not dependent on new protein synthesis, was independent of TNFa, and occurred at the level of gene transcription [26].…”

“…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 neutrophils are costimulated with IFN-c along with LPS, but not with IFN-c or LPS alone, contrary to what happens in monocytes, macrophages, dendritic cells and other cell types [5,6,10].…”

“…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 neutrophils are costimulated with IFN-c along with LPS, but not with IFN-c or LPS alone, contrary to what happens in monocytes, macrophages, dendritic cells and other cell types [5,6,10]. Our studies additionally revealed that neutrophils can also express and release CXCL10 in response to IFN-b in combination with LPS, or to IFN-c together with either TNF-a or IL-1b [6].…”

“…Our previous studies on CXCL10 expression [5,6] used a commercial LPS preparation that may have been contaminated with TLR2-activating agonists [12]. It was therefore necessary to perform experiments with Ultrapure LPS that only activates neutrophils via TLR4.…”