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Journal of Immunology Research
Volume 2015, Article ID 328146, 7 pages
http://dx.doi.org/10.1155/2015/328146
Research Article

IL-34 Suppresses Candida albicans Induced TNFα Production in M1 Macrophages by Downregulating Expression of Dectin-1 and TLR2

1Tissue Engineering and Reparative Dentistry, School of Dentistry, Cardiff University, Heath Park, Cardiff CF14 4XY, UK
2Tianjin Key Laboratory of Biomaterial Research, Institute of Biomedical Engineering, Chinese Academy of Medical Science, Tianjin 300192, China

Received 20 February 2015; Accepted 30 April 2015

Academic Editor: Pedro Giavina-Bianchi

Copyright © 2015 Rong Xu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Candida albicans is a fungus that is an opportunistic pathogen of humans. Normally, C. albicans exists as a harmless commensal and does not trigger inflammatory responses by resident macrophages in skin mucosa, which may be caused by a tolerance of skin macrophage to C. albicans. IL-34 is a recently discovered cytokine, constitutively expressed by keratinocytes in the skin. IL-34 binds to the receptor of M-CSF, thereby stimulating tissue macrophage maturation and differentiation. Resident macrophages exhibit phenotypic plasticity and may transform into inflammatory M1 macrophages for immunity or anti-inflammatory M2 macrophages for tissue repair. M1 macrophages produce higher levels of inflammatory cytokines such as TNFα in response to C. albicans stimulation. In this study, it was demonstrated that IL-34 attenuated TNFα production by M1 macrophages challenged with heat killed Candida (HKC). The molecular mechanism of IL-34 mediated suppression of HKC induced TNFα production by M1 macrophages was by the inhibition of M1 macrophage expression of key C. albicans pattern recognition receptors (PPRs), namely, Toll-like receptor (TLR) 2 and Dectin-1. The results of this study indicated that constitutive IL-34 expressed by skin keratinocytes might suppress resident macrophage responses to C. albicans colonisation by maintaining low levels TLR2 and Dectin-1 expression by macrophages.