Lipopolysaccharide-Induced M2 to M1 Macrophage Transformation for IL-12p70 Production Is Blocked by Candida albicans Mediated Up-Regulation of EBI3 Expression

Abstract

Macrophages are heterogeneous cell populations that are present in all tissues. Macrophages can be divided into classically activated inflammatory macrophages (M1) and alternatively activated anti-inflammatory macrophages (M2). It has been generally accepted that M1 macrophages are polarised in an inflammatory environment to produce pro-inflammatory cytokines, whilst M2 macrophages are involved in anti-inflammation and aid tissue repair in wound healing. Bacterial endotoxin (lipopolysaccharide; LPS) is a potent factor in infection, which induces M1 macrophages resulting in higher levels of iNOS, TNFα and IL-12p70 which dictate inflammatory T cell responses. M2 macrophages can be transformed into M1 macrophages following LPS stimulation to promote inflammation. Candida albicans is a commensal fungal microorganism, which has been suggested to induce immune tolerance; however, the mechanism of C. albicans-induced immune tolerance has not been investigated in detail. IL-35 is a recently identified anti-inflammatory cytokine which is a heterodimeric protein consisting of the Epstein-Barr virus-induced gene 3 (EBI3) and IL-12p35. IL-35 shares the protein subunit p35, with IL-12p70. IL-12p70 is the most potent cytokine to induce Th1 responses during inflammation. In this study, we demonstrate that heat-killed C. albicans (HKC) strongly suppressed LPS-induced IL-12p70 production in M2 macrophages. Candida albicans induced a high level of EBI3 expression in M2 macrophages, which served as a mechanism for IL-12p70 suppression by competitive binding of the common protein subunit (p35) of IL-35 and IL-12p70. To demonstrate that EBI3 expression had the ability to block IL-12p70 production intracellularly, a Chinese Hamster Ovary (CHO) cell line with biscistronic expression of IL-12p40 and p35 was constructed, followed by ectopic over-expression of EBI3. The over-expression of EBI3 in the IL-12p70 producing cell line effectively suppressed IL-12p70 production. IL-35 secretion was also detected in the cell line, with suppressed IL-12p70 production by immune-precipitation Western blotting. However, this secretion was not evident in M2 macrophages following stimulation by HKC. This can be explained by the constitutive expression of IL-35 receptors (gp130 and IL-12Rβ2) in M2 macrophages for cytokine consumption. Our results have indicated that C. albicans can suppress host inflammatory responses in mucosal skin by suppressing LPS-induced IL-12p70 production. Lower IL-12p70 production may avoid an unnecessary Th1 response in order to retain immune tolerance, which may be one of the mechanisms by which C. albicans achieves a successful commensal lifestyle without having a detrimental effect on the host’s health.

A novel IL‐23p19/Ebi3 (IL‐39) cytokine mediates inflammation in Lupus‐like mice

“…LPS also suppressed Ebi3 mRNA expression in a mouse macrophage line RAW264.7 cells (Supporting Information Fig. 1) consistent with the previous report that Ebi3 expression is decreased in LPS-induced M2 to M1 macrophage transformation [39]. These results suggest that the complex effects of LPS on p19 and Ebi3 expression in DCs, macrophages and B cells require additional studies.…”

Gadolinium-based compounds induce NLRP3-dependent IL-1β production and peritoneal inflammation

“…Most studies on M2 function have failed to take into account the importance of a priming signal, normally delivered by a toll-like receptor (TLR) ligand, in inflammasome activation. Priming macrophages with LPS for longer than was done in this study can also shift macrophage polarisation 53. In our study, primed M1′ and M2′ macrophages still expressed typical M1 and M2 markers.…”

Monocyte and Macrophage Plasticity in Tissue Repair and Regeneration

“…Lipopolysaccharide (LPS) has been reported to induce an M1 phenotype from an M2 phenotype. 77 Furthermore, tumor-mediated M2-like macrophages can be reprogrammed to M1-like cells by activation of CD40 using IFN-g. 78 Furthermore, reports have indicated that when fully polarized M2 macrophages present antigen to Th1 cells in a tumor milieu, this interaction results in repolarization of M2 to M1 macrophages. 79 …”