A human 3D immune competent full-thickness skin model mimicking dermal dendritic cell activation.

We have integrated dermal dendritic cell surrogates originally generated from the cell line THP-1 as central mediators of the immune reaction in a human full-thickness skin model. Accordingly, sensitizer treatment of THP-1-derived CD14-, CD11c+ immature dendritic cells (iDCs) resulted in the phosphorylation of p38 MAPK in the presence of 1-chloro-2,4-dinitrobenzene (DNCB) (2.6-fold) as well as in degradation of the inhibitor protein kappa B alpha (IκBα) upon incubation with NiSO4 (1.6-fold). Furthermore, NiSO4 led to an increase in mRNA levels of IL-6 (2.4-fold), TNF-α (2-fold) and of IL-8 (15-fold). These results were confirmed on the protein level, with even stronger effects on cytokine release in the presence of NiSO4: Cytokine secretion was significantly increased for IL-8 (147-fold), IL-6 (11.8-fold) and IL-1ß (28.8-fold). Notably, DNCB treatment revealed an increase for IL-8 (28.6-fold) and IL-1ß (5.6-fold). Importantly, NiSO4 treatment of isolated iDCs as well as of iDCs integrated as dermal dendritic cell surrogates into our full-thickness skin model (SM) induced the upregulation of the adhesion molecule clusters of differentiation (CD)54 (iDCs: 1.2-fold; SM: 1.3-fold) and the co-stimulatory molecule and DC maturation marker CD86 (iDCs ~1.4-fold; SM:~1.5-fold) surface marker expression. Noteworthy, the expression of CD54 and CD86 could be suppressed by dexamethasone treatment on isolated iDCs (CD54: 1.3-fold; CD86: 2.1-fold) as well as on the tissue-integrated iDCs (CD54: 1.4-fold; CD86: 1.6-fold). In conclusion, we were able to integrate THP-1-derived iDCs as functional dermal dendritic cell surrogates allowing the qualitative identification of potential sensitizers on the one hand, and drug candidates that potentially suppress sensitization on the other hand in a 3D human skin model corresponding to the 3R principles ("replace", "reduce" and "refine").

Extending the applicability domain of the human cell line activation test (h-CLAT).

Cosmetic ingredients must be toxicologically assessed to determine their skin sensitizing potential. The in vitro human cell line activation test (h-CLAT; OECD TG 442E) addresses the activation of dermal dendritic cells by analyzing specific protein expression after exposure of THP-1 cells to the test chemical. According to the protocol, FITC-labeled antibodies are used for protein detection. However, some chemicals show strong autofluorescence at FITC-specific wavelengths so that antibody-specific signals cannot be distinguished appropriately from autofluorescence background. This leads to inconclusive or false-negative predictions. Alternative fluorochromes can be used if their equivalence with the FITC-labeled antibodies is proven. In the current paper we describe the results of a proficiency exercise, based on the proficiency chemicals listed in the guideline, with FITC-labeled antibodies as the benchmark and APC-labeled anti­bodies as an alternative detection system. APC emits fluorescence at longer wavelengths, thus avoiding interference in the FITC spectrum. Irrespective of the employed fluorochrome, all chemicals were classified correctly, and the EC150 and 200 values were in the same order of magnitude. Hence, the equivalence in performance of FITC- and APC-labeled antibodies was demonstrated, and the respective demand of the guideline was fulfilled. In a case study, we then tested a proprietary oxidative hair dye using both fluorochromes. Using APC-labeled antibodies, the hair dye was unambiguously identified as a sensitizer, whereas no classification could be made with the FITC-labeled antibodies. With APC, fluorescence interference can be circumvented and the applicability domain of the h-CLAT extended to include autofluorescent chemicals.

In vitro detection of contact allergens: development of an optimized protocol using human peripheral blood monocyte-derived dendritic cells.

Allergic contact dermatitis is a delayed T-cell mediated allergic response associated with relevant social and economic impacts. Animal experiments (e.g. the local lymph node assay) are still supplying most of the data used to assess the sensitization potential of new chemicals. However, the 7th amendment to the EU Cosmetic Directive will introduce a testing ban for cosmetic ingredients after 2013. In vitro alternative methods are thus being actively developed. Although promising results have been obtained with cell lines, their reduced functionality and inherent genomic instability led us to reinvestigate the use of peripheral blood monocyte-derived dendritic cells (PBMDCs) for the establishment of a reliable in vitro sensitization test. To solve the issues associated with the use of primary cells, the culture and exposure conditions (cytokine concentrations, incubation time, readout, pooled vs. single donors and cytotoxicity) were re-assessed and optimized. Here we propose a stable and reproducible protocol based on PBMDCs. This should allow a wider acceptance of PBMDCs as a reliable test system for the detection of human skin sensitizers and the inclusion of this protocol in an integrated testing strategy.