Nickel Sulfate Promotes IL-17A Producing CD4+ T Cells by an IL-23-Dependent Mechanism Regulated by TLR4 and Jak-STAT Pathways

Allergic contact dermatitis, caused by nickel, is a delayed-type hypersensitivity reaction, and 14.5% of the general population may be affected in Europe. Among a wide range of cytokines, the IL-12 family has unique structural and immunological characteristics. Whereas IL-12p70 promotes T helper (Th) 1 cell polarization, IL-23 promotes Th17 cell development and both have been isolated from nickel-allergic patients. In this work, we were interested in understanding the mechanism behind nickel-induced Th17 cell development. We showed that nickel induced an early production of IL-23 in human monocyte-derived dendritic cells along with an increase in the expression of il-23p19 and il-12p40 mRNA. However, the production of a significant level of IL-12p70 required an additional signal such as IFN-γ. Moreover, nickel-treated monocyte-derived dendritic cells induced an increase in the percentage of IL-17A+ CD4+ T cells, an effect reduced by IL-23 neutralization. We then investigated the molecular mechanism of IL-23 production. Our results showed that toll-like receptor 4, p38 mitogen-activated protein kinase, and NF-κB were involved in IL-23 production induced by nickel. However, Jak-signal transducer and activator of transcription activation seems to maintain the IL-23/IL-12p70 balance by limiting IL-23 production and promoting Th1 polarization. These results indicate that nickel-induced Th17 cell development is dependent on the production of IL-23 by human monocyte-derived dendritic cells via toll-like receptor 4, p38 mitogen-activated protein kinase, NF-κB, and Jak-signal transducer and activator of transcription pathways.