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Study of the functional role of the distinct skin dendritic cell subsets in vivo

Final Report Summary - ROLE OF SKIN DCS (Study of the functional role of the distinct skin dendritic cell subsets in vivo)

Objective

Combine cellular and molecular techniques to study the role of DC subsets in vivo. Candidate genes underlying the functional diversity of the distinct DC subsets were to be sought (part I and II), and in parallel, an innovative KI mouse model restricting the antigen-presenting capacity to one particular DC subset was to be constructed (part III) to allow study of the specific role of that particular DC subsets in vivo (part IV).

Performed work

Part I: Characterisation of DC subsets
Unexpectedly, by characterising conventional skin dendritic cells (DCs) we identified a previously unappreciated monocyte-derived DC population (MoDCs). Therefore, we designed a novel gating-strategy allowing the proper distinction of DCs and MoDCs. Next, we found that CD11b+ DCs express the Aldh1a2 gene, which codes for the ALDH enzyme necessary for retinoic acid production. In addition, through collaboration with the team of Dr Dalod we extended our findings to human DC subsets using micro-array data generated by both teams and proposed a simplified classification of human and mouse dendritic cell subsets (Guilliams, EJI, 2010).

Part II: Study of DC subsets in vitro
All the identified DC subsets were isolated and their capacity to generate regulatory T cells in vitro was assessed. Doing so, we were able to demonstrate that the particular CD11b+ DC subset expressing Aldh1a2 (part I) is endowed with the specific capacity to generate induced regulatory T cells via a retinoic acid dependent mechanism (Guilliams, Blood, 2010).

Part III: Construction of a KI mouse
As we had unexpectedly discovered the presence of new DC and macrophage subsets within the skin, we decided to not only construct the Langerin-Ea KI mice but also to launch the construction of a second ROSA-Ea KI mouse that would be more flexible and that would allow to target not only Langerin-expressing DCs (as planned originally) but also the new DC subsets we had identified.

Part IV: Study of DC subsets in vivo
While the Langerin-Ea KI mice displayed a rather low MHCII I-E expression, the ROSA-Ea KI mouse yielded high MHC II I-E expression. Therefore, we crossed the ROSA-Ea KI mice with Langerin-KI mice to obtain Langerin+ DCs with high MHCII I-E expression. Yet, the necessity to cross the ROSA-Ea on the Langerin-KI mice delayed the use of these KI mice for the planned, long term in vivo studies and as a result these experiments are currently being finalised. Nevertheless, in the mean time we applied our novel gating strategy (part I) to study the role of the distinct DC subsets during three different inflammation models: a skin irritation model, a vaccination model and a colitis model. We are currently writing three separate manuscripts summarising these results. In parallel, we will continue to work on the KI mice to finalise this part of the IEF scientific project. Importantly, the flexibility provided by our ROSA-Ea KI system will also allow us to use this research strategy on more DC subsets than was originally envisaged and these mice will be the cornerstone of a new research project involving the collaboration of three European research teams.

Main results and impact

Major achievements include:
1) the identification of a skin DC subset endowed with the specific capacity to generate regulatory T cells;
2) a simplified classification of human and mouse dendritic cell subsets;
3) a novel gating strategy allowing the proper identification of conventional DC subsets, MoDCs and macrophages;
4) an in-depth analysis of the function of the distinct DC subsets during skin inflammation, vaccination and colitis; and
5) the generation of a novel KI mouse model which allows to express MHCII I-E on distinct subsets of DCs.
This IEF project has pointed out that the distinct DC subsets possess a strikingly different migratory behaviour and immunostimulatory potential. This has important consequences for the development of novel immunotherapies and the design of more effective vaccines.