TOLEROGENIC EFFECT OF ECTOPIC IL-35IG PRODUCED BY DENDRITIC CELLS IS MEDIATED BY ARGINASE 1
- Maria Laura Belladonna, Italy
Abstract
Background and Aims
IL-35 is a potent immunosuppressive cytokine. Dendritic cells (DCs) are specialized antigen presenting cells directing immune response toward immunity or tolerance depending on many factors, including cytokine milieu and immunoregulatory enzymes. Indoleamine 2,3-dioxigenase 1 (IDO1) and Arginase 1 (Arg1) are metabolic enzymes that, expressed by dendritic cells, contribute to immunoregulation. We aimed to understand the possible role of IDO1 and Arg1 enzymes as potential immunometabolic effectors downstream tolerogenic ectopic IL‐35Ig.
Methods
We transfected a single chain IL-35Ig gene construct in murine splenic DCs (DC35) and assessed any IDO1 and Arg1 activities as resulting from ectopic IL-35Ig expression. In vitro, modulation of Ido1 and Arg1 genes was evaluated by real-time PCR; in vivo, a negative vaccination strategy exploiting peptide-loaded DC35 was set up in order to induce antigen-specific tolerance in mice subsequently challenged with the same peptide in a DTH experiment.
Results
Unlike Ido1, Arg1 expression was induced in vitro in DC35 and conferred an immunosuppressive phenotype on those cells, as revealed by a DTH assay. In particular, the suppressive response obtained in the control group with wild-type DC35 was still observed when IDO1 function was lost in DC35 (Ido–/– DC35); on the contrary, it was reverted by Arg1 inhibition in DC35 with the specific catalytic inhibitor nor-NOHA. Moreover, the in vivo onset of a tolerogenic phenotype in DC35 was associated with the detection of CD25+CD39+, rather than Foxp3+, regulatory T cells.
Conclusions
Arg1, but not Ido1, expression in DC35 appears to be an early event responsible for IL-35Ig–mediated immunosuppression observed in DC35-treated mice.