Summary Dendritic cells (DCs) mediate interactions between innate and specific immunity and may induce regulatory mechanisms. We investigated the effects of modulated DCs in mice with collagen‐induced arthritis (CIA) and tested the responses of cells to induced naturally occurring regulatory T cells. DCs were stimulated or not with DNA or lipopolysaccharide (LPS) for 24 hr. DC maturation was assayed, and then modulated DCs were intraperitoneally injected on day 14 into DBA/1 mice to treat CIA. In addition to arthritis scores and type 2 collagen (CII) response, the induction of CD4+ CD25+ T cells was analysed by flow cytometry in peripheral blood and the expression of Foxp3, transforming growth factor (TGF)‐β, interleukin (IL)‐10 and cytotoxic T‐lymphocyte antigen (CTLA)‐4 was quantified. Finally, the expression of indoleamine‐2,3‐dioxygenase (IDO) was assayed in DCs. In comparison with LPS‐stimulated DCs, plasmid‐stimulated DCs expressed lower levels of major histocompatibility complex (MHC) class II, CD40, CD80 and CD86 molecules and secreted less IL‐12p70, interferon (IFN)‐γ, IL‐10 and TNF‐α, displaying a semi‐mature phenotype. Compared with non‐stimulated DCs, stimulated DCs improved arthritis scores when injected after immunization, without modifying the T helper type 1 (Th1)/Th2 balance of the immune response against collagen. Stimulated DCs induced markers for regulatory T cells (Foxp3, TGF‐β1 and CTLA‐4) in vivo. Only LPS‐stimulated DCs expressed IDO, which may explain their better therapeutic efficacy. Regulatory mechanisms were induced using DCs modulated by innate immunity stimulators. Innate immunity mechanisms do not require the presence of the disease‐causing antigen, even in T‐ and B‐cell specific diseases. Our results have implications for the treatment of rheumatoid arthritis, an autoimmune disease whose triggering antigen has not been identified, and substantially clarify the role of regulatory T cells in CIA.

SummaryDendritic cells (DC) play a pivotal role in tolerance. Adrenomedullin (AM), a neuropeptide with anti-apoptotic and anti-inflammatory effects, may decrease T helper type 1 effector cells and induce regulatory T (Treg) cells. The aim of this study was to evaluate AM effects on murine dendritic cell (DC) maturation and functions. Bone marrow-derived DC were produced and stimulated with CpG motifs, lipopolysaccharide or AM for 24 hr. Then, DC maturation and expression of AM and AM receptors were evaluated. Compared with lipopolysaccharide-stimulated or CpGstimulated DC, AM-stimulated DC had lower levels of co-stimulatory molecule expression and pro-inflammatory cytokine release. The AM induced high levels of interferon-c but not of interleukin-10. Importantly, AM inhibited lipopolysaccharide-induced maturation of DC. However, allogeneic T-cell stimulation and endocytic capacity of AM-stimulated DC were comparable to those of semi-mature and mature DC. Moreover, DC expressed AM and its receptors at a basal level, and AM receptor expression increased with DC maturation. The AM stimulation induced indoleamine 2,3-dioxygenase (IDO) expression, promoting Treg cell expansion. For the first time, we describe the DC maturation phenotype by a neuropeptide (AM). We have demonstrated that AM and its receptors are expressed in DC and that exogenous AM can modify the DC phenotype and functions and can induce a semi-mature DC phenotype with IDO expression. These results indicate close interactions among immune system regulation mechanisms and calcitonin-like peptides.