title: 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.
authors.affiliation: Tissue Engineering and Reparative Dentistry, School of Dentistry, Cardiff University, Heath Park, Cardiff, United Kingdom.
authors.forename: Xing-Feng
authors.initials: XF
authors.lastname: Zheng
authors.forename: Yu-Xiao
authors.initials: YX
authors.lastname: Hong
authors.forename: Gui-Jie
authors.initials: GJ
authors.lastname: Feng
authors.forename: Gao-Feng
authors.initials: GF
authors.lastname: Zhang
authors.forename: Helen
authors.initials: H
authors.lastname: Rogers
authors.forename: Michael A O
authors.initials: MA
authors.lastname: Lewis
authors.forename: David W
authors.initials: DW
authors.lastname: Williams
authors.forename: Zhao-Fan
authors.initials: ZF
authors.lastname: Xia
authors.forename: Bing
authors.initials: B
authors.lastname: Song
authors.forename: Xiao-Qing
authors.initials: XQ
authors.lastname: Wei
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells; D016466:CHO Cells; D002176:Candida albicans / Q000276:immunology*; D002460:Cell Line; D003412:Cricetulus; D015870:Gene Expression; D005786:Gene Expression Regulation; D018664:Interleukin-12 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000276:immunology*; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism* / Q000382:microbiology; D051379:Mice; D015778:Minor Histocompatibility Antigens; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018121:Receptors, Cytokine / Q000235:genetics* / Q000378:metabolism
chemical_list: C499601:Ebi3 protein, mouse; D008070:Lipopolysaccharides; D015778:Minor Histocompatibility Antigens; D012333:RNA, Messenger; D018121:Receptors, Cytokine; D018664:Interleukin-12