Gold nanoparticles (GNPs) are claimed as outstanding biomedical tools for cancer diagnostics and photo-thermal therapy, but without enough evidence on their potentially adverse immunological effects. Using a model of human dendritic cells (DCs), we showed that 10 nm- and 50 nm-sized GNPs (GNP10 and GNP50, respectively) were internalized predominantly via dynamin-dependent mechanisms, and they both impaired LPS-induced maturation and allostimulatory capacity of DCs, although the effect of GNP10 was more prominent. However, GNP10 inhibited LPS-induced production of IL-12p70 by DCs, and potentiated their Th2 polarization capacity, while GNP50 promoted Th17 polarization. Such effects of GNP10 correlated with a stronger inhibition of LPS-induced changes in Ca2+ oscillations, their higher number per DC, and more frequent extra-endosomal localization, as judged by live-cell imaging, proton, and electron microscopy, respectively. Even when released from heat-killed necrotic HEp-2 cells, GNP10 inhibited the necrotic tumor cell-induced maturation and functions of DCs, potentiated their Th2/Th17 polarization capacity, and thus, impaired the DCs' capacity to induce T cell-mediated anti-tumor cytotoxicity in vitro. Therefore, GNP10 could potentially induce more adverse DC-mediated immunological effects, compared to GNP50.

CD4(+)CD25(hi)Foxp3(+) regulatory T-cells (Tregs) are of crucial importance in regulating the immune response, including the control of any defense against infection. Their presence in periapical lesions has not been demonstrated, as yet. We hypothesized that Tregs infiltrate periapical lesions, where they inhibit T-cell proliferation. The aim of this study was to characterize Tregs in periapical lesions by confocal microscopy, flow cytometry, and functional assays. We showed that CD4(+)CD25(hi)Foxp3(+) cells in periapical lesions expressed IL-10 and TGF-beta. Their frequency was significantly higher than in peripheral blood and correlated with the levels of TGF-beta and IL-10 in culture supernatants of periapical lesion mononuclear cells. Tregs inhibited the proliferation of responder T-cells in vitro, at least in part, by stimulating the production of IL-10. These findings suggest that CD4(+)CD25(hi)Foxp3(+) cells in periapical lesions may play regulatory roles in controlling local immune/inflammatory processes.

Immunoregulatory mechanisms within periapical lesions (PLs) are as of yet unexplored. Considering the crucial role of DCs in controlling the immune response within PLs, the immunomodulatory properties of mesenchymal stem cells (MSCs), and the colocalization of MSCs and DCs in situ, we wondered whether MSCs from PLs modulate the development and functions of DCs. Using a model of monocyte-derived DCs, we showed that PL-MSCs inhibited differentiation of DCs via soluble factors, of which IL-6 had a minor effect, but did not impair their subsequent maturation induced by pro-inflammatory cytokines. However, upon maturation such DCs favored the production of Th2/Th17 cytokines by allogenic CD4 + lymphocytes in coculture, compared with mature DCs differentiated without PL-MSCs. PL-MSC-differentiated DCs, cultivated with pro-inflammatory cytokines and PL-MSCs, although phenotypically mature, exhibited poor allostimulatory activity, induced anergy, Th2 polarization, differentiation of suppressive CD4 + CD25 high CD39 + Treg-cell subsets via IDO-1-, ILT-3-, and ILT-4-dependent mechanisms, and increased production of TGF-β in the coculture. In contrast, DCs cultivated with PL-MSCs only during maturation stimulated proliferation and Th1 polarization of CD4 + T cells in an IL-12-independent manner. In conclusion, PL-MSCs significantly modulate the development and functions of DCs, depending on the phase of DCs development during which the interaction occurs. Keywords: Dendritic cells r Mesenchymal stem cells r Periapical lesions r Th polarizationAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionPeriapical lesions (PLs) are a common pathology within the human population initiated by the bacterial invasion of the root canal and develop from an acute inflammatory response to the formation of granulomas or cysts infiltrated by various inflammatory cells [1].Correspondence: Prof. MiodragČolić e-mail: fakultet.vma@mod.gov.rs Furthermore, cytokines produced by Th cells have been shown to play a crucial role in PLs pathogenesis. Namely, Th1-and Th17-derived cytokines promote inflammation, bone resorption, and disease progression. Th2 cells seem to be important for the later phases of PLs development, whereas IL-10 and TGF-β produced by Treg cells seem to be important for the healing processes within PLs [2,3]. However, it is not yet clear which mediators and cells are involved crucially in the regulation of Th-cell commitment during the development, maintenance, and resolution of the disease.C 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2013. 43: 1862-1872 Immunomodulation 1863DCs are the key regulatory and decision-making cells with a unique ability to activate naive T cells and polarize their development. These cells can be differentiated in vitro from monocytes or CD34 + -progenitors with GM-CSF and IL-4, generating CD1a + CD14 − immature DCs (iDCs) [4]. Alternatively, in the absence of IL-4, GM-CSF induces the differ...

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