Journal Article

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

Lewis, Michael A. O., Hong, Yu-Xiao, Xia, Zhao-Fan, Wei, Xiao-Qing, Williams, David W., Rogers, Helen, Feng, Gui-Jie, Zheng, Xing-Feng, Zhang, Gao-Feng, Song, Bing

2013

Overview

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.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Animals / Bacteria / Biology / Bone marrow / Bone Marrow Cells / Candida albicans / Candida albicans - immunology / Cell Line / CHO Cells / Cricetulus / Cytokines / Dentistry / Dermatitis / Endotoxins / Epstein-Barr virus / Gene Expression / Gene Expression Regulation / Genetic transformation / Glycoprotein gp130 / Hospitals / Immunological tolerance / Immunology / Infections / Inflammation / Interleukin 12 / Interleukin-12 - biosynthesis / Kinases / Lipopolysaccharides / Lipopolysaccharides - immunology / Lymphocytes T / Macrophages / Macrophages - immunology / Macrophages - metabolism / Macrophages - microbiology / Medicine / Metabolism / Mice / Minor Histocompatibility Antigens / Mucosa / Nitric-oxide synthase / Overexpression / Phenotype / Receptors / Receptors, Cytokine - genetics / Receptors, Cytokine - metabolism / RNA, Messenger - genetics / RNA, Messenger - metabolism / Skin / Stimulation / Tissue engineering / Transformation / Tumor necrosis factor-TNF / Tumor necrosis factor-α / Viruses / Western blotting / Wound healing