M‐CSF induces the expression of a membrane‐bound form of IL‐18 in a subset of human monocytes differentiating in vitro toward macrophages

Abstract

IL-18 is a proinflammatory cytokine belonging to the "IL-1 family" that has been shown to play a prominent role in the induction of type 1 immune responses. Here, we show that M-CSF induces the expression of a membrane-bound form of IL-18 (mIL-18) in a subset of human blood monocytes differentiating toward macrophages. While monocytes, DC, and GM-CSF-treated monocytes did not express mIL-18, its expression was detected in ap- IntroductionMacrophages produce IL-1 (IL-1α and IL-1β) and IL-18, proinflammatory cytokines that have been generally assigned to a larger Correspondence: Dr. Cristina Bottino e-mail: Cristina.Bottino@unige.it group of cytokines termed "IL-1 family" since they present related receptor structures and utilize similar signal transduction * These authors contributed equally to this study.C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2012. 42: 1618-1626 Innate immunity 1619 pathways [1,2]. IL-1α is synthesized as pro-IL-1α, a biologically active precursor that is constitutively present in cells and can be cleaved into a mature cytokine by calpain, a membrane-bound cysteine protease. IL-1α is not readily secreted by cells and remains either bound to plasma membrane [3] or inside the cells where it acts as an autocrine growth factor. IL-1β, the prototype of primary proinflammatory cytokines is not present in cells under steady state conditions. Its production is highly regulated and requires a first signal-inducing de novo transcription of the gene and accumulation of the inactive precursor cytokine (pro-IL-1β) and a second signal-driving inflammasome assembly [4] and activation of caspase-1 (also known as IL-1β-converting enzyme, ICE), which converts pro-IL-1β into the IL-1β bioactive mature cytokine. These signals are provided by pathogen-associated molecular patterns (PAMPs) that act through specific receptors such as Toll-like receptors (TLRs), cytokines such as IL-33, IL-1β itself, and IL-1α, which is released passively upon cell injury, danger-associated molecular patterns (DAMPs) such as urate crystals or pathogenic dusts and extracellular ATP, which after binding to P2 receptors (P2R) induces a rapid exit of potassium from the cell. Interestingly, also a caspase-1 independent type of IL-1β activation has been described. Thus, in different models of sterile inflammation, macrophages and monocytes would be able to release pro-IL-1β that is cleaved by proteinase-3 produced by neutrophils [1,5]. IL-18 originally identified as an IFN-γ-inducing factor (IGIF), has been shown to play a prominent role in the induction of type 1 immune responses [1,6,7]. Although belonging to the same cytokine family, IL-18 and IL-1β display both similarities and important differences [1,2]. Similar to IL-1β, IL-18 is synthesized as a biologically inactive precursor peptide (pro-IL-18) that is subsequently cleaved by caspase-1. Unlike IL-1β, however, PAMPs such as LPS while inducing IL-18 release have little impact on IL-18 gene transcription [2].Monocytes are a considerable r...

TLR activation of tumor‐associated macrophages from ovarian cancer patients triggers cytolytic activity of NK cells

“…1). In line with previous data [14,18], mIL-18 showed a bimodal distribution and was detected in a subset (30-40%) of in vitro-derived M2 cells. IIIc PT2 71 IIIc PT3 76 IIIc PT4 83 IIIc PT5 41 IIIc PT6 77 IIIc PT7 60 IIIc PT8 57 IIIc PT9 75 IIIc PT10 44 IIIc PT11 67 IV PT12 72 IIIc PT13 67 IIIc PT14 59 IV PT15 86 IIIc PT16 77 IIIc On the other hand, mIL-18 was expressed by most ex vivo-purified TAMs and its surface density was significantly higher than in M2 cells (Fig.…”

“…Notably, a subset (30-40%) of M2 cells expressed a membrane-bound form of IL-18 (mIL-18) that was released upon TLR stimulation. This soluble form of IL-18 (sIL-18), by acting in close cell-to-cell contact, was crucial for both IFN-γ release and expression of CCR7 by NK cells [18]. Here, we analyzed the surface phenotype and functional properties of NK cells and TAMs from ovarian cancer patients as well as the functional outcome of the interaction between TAMs and freshly isolated NK cells.…”

IL‐18 associates to microvesicles shed from human macrophages by a LPS/TLR‐4 independent mechanism in response to P2X receptor stimulation

“…IL-18 potentiates the immune response against viruses but has also been linked to the pathogenesis of atherosclerosis, active psoriasis, systemic lupus erythematosus, rheumatoid arthritis, Crohn's disease, and graftversus-host disease [44]. It has recently been reported that besides the soluble form, IL-18 is expressed as a membrane-bound protein in human blood CD16 − and CD16 + monocytes differentiating to macrophages by M-CSF stimulation [45].Human macrophages were chosen as a cell model for this study since they produce IL-18 and express several P2 receptor subtypes, particularly P2X7 that has been previously shown to trigger MVs release from other cell types [2,24]. Here we show that stimulation of human macrophages with the pan P2 agonist ATP or the P2X7 agonist BzATP induced shedding of MVs within minutes.…”

Interleukin-18 as a Therapeutic Target in Acute Myocardial Infarction and Heart Failure

“…The p16 fragmentinduced IFN-γ production in vitro but with only approximately 20% of the activity of mature IL-18 (26). Adding supernatant from human CD8 + T cells containing granzyme B (GrB) resulted in cleavage at the same site as caspase-1 and resulted in active IL-18 (27 (30,31). PR3 could also be the mechanism by which pro-IL-1β and pro-IL-18 released from a dying cell are activated.…”