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Monocytes/macrophages are key players in all phases of physiological and pathological inflammation. To understanding the regulation of macrophage functional differentiation during inflammation, we designed an in vitro model that recapitulates the different phases of the reaction (recruitment, initiation, development, and resolution), based on human primary blood monocytes exposed to sequential changes in microenvironmental conditions. All reaction phases were profiled by transcriptomic microarray analysis. Distinct clusters of genes were identified that are differentially regulated through the different phases of inflammation. The gene sets defined by GSEA analysis revealed that the inflammatory phase was enriched in inflammatory pathways, while the resolution phase comprised pathways related to metabolism and gene rearrangement. By comparing gene clusters differentially expressed in monocytes vs. M1 and vs. M2 macrophages extracted from an in-house created meta-database, it was shown that cells in the model resemble M1 during the inflammatory phase and M2 during resolution. The validation of inflammatory and transcriptional factors by qPCR and ELISA confirmed the transcriptomic profiles in the different phases of inflammation. The accurate description of the development of the human inflammatory reaction provided by this in vitro kinetic model can help in identifying regulatory mechanisms in physiological conditions and during pathological derangements.

IntroductionInterleukin (IL)-11 is a multifunctional cytokine that was originally isolated from the primate stromal cell line, PU-34, and later from the human MRC 5 cell line. Biologic characterization has shown diverse effects on a variety of hematopoietic and nonhematopoietic cell types (reviewed in reference 1). Due to its ability to stimulate megakaryopoiesis and thrombopoiesis, IL-11 has been approved in the United States for the treatment of chemotherapy-induced thrombocytopenia. In addition to stimulating hematopoietic progenitor cells, 2 IL-11 exerts a strong anti-inflammatory activity in vitro and in vivo. By inhibiting nuclear translocation of nuclear factor-kB (NF-kB), 3 IL-11 reduces production by macrophages of proinflammatory cytokines such as tumor necrosis factor-␣ (TNF-␣), IL-1␤, Therapeutic applications of this effect in multiple animal models of inflammatory disorders have reduced signs of disease. 4,5,[7][8][9] In a well-characterized murine model of graftversus-host disease (GVHD) directed at major histocompatibility complex (MHC) and minor antigens, IL-11 strongly inhibited GVHD and enhanced recipient survival. 10 These effects were due to protection of the small bowel from irradiation and GVHD toxicity, suppression of TNF-␣, and polarization of donor T cells to a Th2 response with decreased interferon-␥ (IFN-␥) and augmented IL-4 production. 10 Interestingly, a significant reduction of CD4-dependent GVHD was not associated with impairment of the cytolytic function and graft-versusleukemia (GVL) effect of CD8 ϩ T cells. 11 Thus, a short course of IL-11 treatment before allogeneic stem cell transplantation has been proposed to help separate the GVL effect from GVHD. 11 Recently, IL-11 therapy has been administered to patients with psoriasis in a phase I clinical dose-escalation trial. 12 The treatment led to down-regulation of type I cytokines in psoriatic lesions and reduction of keratinocyte proliferation and cutaneous inflammation.Taken together, these studies have revealed that IL-11 exerts a series of important immunomodulatory effects that can be applied in various therapeutic contexts. However, the issue as to whether T-cell polarization is solely due to IL-11-mediated suppression of IL-12 or whether IL-11 has additional direct effects on CD4 ϩ CD45RA ϩ naive T cells has yet to be addressed. The most potent antigen-presenting cells (APCs) involved in the stimulation of naive CD4 ϩ cells are dendritic cells (DCs), which induce type I responses by their ability to produce IL-12 on maturation. 13 In this study, we investigated the immunomodulatory effects of IL-11 on monocytes, human monocyte-derived DCs (Mo-DCs), and T cells. Our results demonstrate that IL-11 regulates immune responses by at least 2 potent mechanisms of action: it inhibits IL-12 production by monocytes and exerts a direct effect on CD4 ϩ Th cell polarization. The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''...