GM-CSF and IL-3 Modulate Human Monocyte TNF-α Production and Renewal in In Vitro Models of Trained Immunity

Abstract

GM-CSF and IL-3 are hematopoietic cytokines that also modulate the effector functions of several immune cell subsets. In particular, GM-CSF and IL-3 exert a significant control on monocyte and macrophage effector functions, as assessed in experimental models of inflammatory and autoimmune diseases and also in human studies. Here, we sought to investigate the mechanisms and the extent to which GM-CSF and IL-3 modulate the pro-inflammatory, LPS-mediated, activation of human CD14+ monocytes taking into account the new concept of trained immunity (i.e., the priming stimulus modulates the response to subsequent stimuli mainly by inducing chromatin remodeling and increased transcription at relevant genetic loci). We demonstrate that GM-CSF and IL-3 priming enhances TNF-α production upon subsequent LPS stimulation (short-term model of trained immunity) in a p38- and SIRT2-dependent manner without increasing TNF primary transcript levels (a more direct measure of transcription), thus supporting a posttranscriptional regulation of TNF-α in primed monocytes. GM-CSF and IL-3 priming followed by 6 days of resting also results in increased TNF-α production upon LPS stimulation (long-term model of trained immunity). In this case, however, GM-CSF and IL-3 priming induces a c-Myc-dependent monocyte renewal and increase in cell number that is in turn responsible for heightened TNF-α production. Overall, our results provide insights to understand the biology of monocytes in health and disease conditions in which the hematopoietic cytokines GM-CSF and IL-3 play a role and also extend our knowledge of the cellular and molecular mechanisms of trained immunity.

Molecular Analysis of a Short-term Model of β-Glucans-Trained Immunity Highlights the Accessory Contribution of GM-CSF in Priming Mouse Macrophages Response

“…Our data seem to target GM-CSF as a pivotal actor of the BG-induced priming of macrophages. Consistently with this hypothesis, GM-CSF-treated macrophages/monocytes exposed to TLR2 or TLR4 ligands were shown to produce significantly more IL-1β, IL-6, and TNFα ( 30 , 40 – 42 ). Furthermore, GM-CSF was also able to prevent endotoxin tolerance in macrophages by restoring TNFα production on LPS-tolerized human monocytes ( 43 ).…”

“…Similarly, it was very recently shown that GM-CSF, and IL-3, on its own, was sufficient to train human monocytes in a p38- and SIRT2-dependent manner ( 30 ). In this study, we also observed that GM-CSF pretreatment of mouse macrophages induced a moderate but significant increase of cytokine secretion upon LPS re-stimulation.…”

“…Recent findings highlighted some molecular mechanisms involved in this long-term trained immunity model, including a metabolic shift toward aerobic glycolysis (a feature of cell activation and proliferation) via PI3K/AKT/mTOR pathway ( 28 ) and epigenetic modifications ( 29 ) in BG-trained human monocytes. Although GM-CSF priming was very recently shown to increase responsiveness to lipopolysaccharide (LPS) in a short-term model of training ( 30 ), less is known regarding its role in BG-related trained immunity.…”

The investigation of immunomodulatory activities of Gloeostereum�incaratum polysaccharides in cyclophosphamide-induced immunosuppression mice

“…T helper (Th) cells, one of subsets of T cells, mediates the production of ILs, which can active immune cells during immune response evidencing by huper-levels of IL-2 activates pro-inflammatory CD4 + T cells (33). IL-3 participates in regulating myeloid cell expansion, autoimmunity and modulate human CD14 + monocyte response in short-term or long-term models of trained immunity (34). IL-6 is a critical factor for maturation, proliferation, differentiation and maintenance of B cells/plasma cells, which seems to enhance the development of pro-inflammatory cell and to inhibit the development T regulatory cells (35).…”

BCG as a Case Study for Precision Vaccine Development: Lessons From Vaccine Heterogeneity, Trained Immunity, and Immune Ontogeny

“…alveolar macrophages (Rothchild et al, 2017) and facilitating containment of virulent mycobacteria in pulmonary granulomas (Szeliga et al, 2008). Interestingly, GM-CSF along with IL-3 priming of CD14+ human monocytes enhanced TNF production and monocyte renewal (as evaluated by the degree of cell confluency and increased cell number by fluorescence and timelapse microscopy) upon subsequent LPS stimulation, indicating a potential mechanism of trained immunity (Borriello et al, 2016). As detailed in the following sections, trained immunity refers to the ability of innate immune cells to mount an enhanced subsequent response to diverse microbes, a phenomenon whose underlying mechanisms are under intense investigation.…”