Neutrophil elastase treated dendritic cells promote the generation of CD4+FOXP3+ regulatory T cells in vitro

We have previously shown that neutrophilic elastase converts human immature dendritic cells (DCs) into TGF-β secreting cells and reduces its allostimulatory ability. Since TGF-β has been involved in regulatory T cells (Tregs) induction we analyzed whether elastase or neutrophil-derived culture supernatant treated DCs induce CD4+FOXP3+ Tregs in a mixed lymphocyte reaction (MLR). We found that elastase or neutrophil-derived culture supernatant treated DCs increased TGF-β and decreased IL-6 production. Together with this pattern of cytokines, we observed a higher number of CD4+FOXP3+ cells in the MLR cultures induced by elastase or neutrophil-derived culture supernatant treated DCs but not with untreated DCs. The higher number of CD4+FOXP3+ T cell population was not observed when the enzymatic activity of elastase was inhibited with an elastase specific inhibitor and also when a TGF-β1 blocking antibody was added during the MLR culture. The increased number of CD4+ that express FOXP3 was also seen when CD4+CD25- purified T cells were cocultured with the TGF-β producing DCs. Furthermore, these FOXP3+ T cells showed suppressive activity in vitro.These results identify a novel mechanism by which the tolerogenic DCs generated by elastase exposure contribute to the immune regulation and may be relevant in the pathogenesis of several lung diseases where the inflammatory infiltrate contains high numbers of neutrophils and high elastase concentrations.