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Summary Understanding the mechanisms fine-tuning immunogenic versus tolerogenic balance in dendritic cells (DCs) is of high importance for therapeutic approaches. We found that NCoR1-mediated direct repression of the tolerogenic program in conventional DCs is essential for induction of an optimal immunogenic response. NCoR1 depletion upregulated a wide variety of tolerogenic genes in activated DCs, which consequently resulted in increased frequency of FoxP3+ regulatory T cells. Mechanistically, NCoR1 masks the PU.1-bound super-enhancers on major tolerogenic genes after DC activation that are subsequently bound by nuclear factor-κB. NCoR1 knockdown (KD) reduced RelA nuclear translocation and activity, whereas RelB was unaffected, providing activated DCs a tolerogenic advantage. Moreover, NCoR1DC−/- mice depicted enhanced Tregs in draining lymph nodes with increased disease burden upon bacterial and parasitic infections. Besides, adoptive transfer of activated NCoR1 KD DCs in infected animals showed a similar phenotype. Collectively, our results demonstrated NCoR1 as a promising target to control DC-mediated immune tolerance., Graphical Abstract, Highlights • NCoR1 directly represses tolerogenic program in mouse cDCs • Depletion of NCoR1 in cDCs enhanced Treg development ex vivo and in vivo • NCoR1 masks PU.1-bound super-enhancers on tolerogenic genes in cDCs • NCoR1DC−/− animals depicted enhanced Treg frequency and infection load, Molecular Mechanism of Gene Regulation; Immunology; Immune Response; Transcriptomics

Th17 cells are often associated with autoimmunity and been shown to be increased in CD11b(-/-) mice. Here, we examined the role of CD11b in murine collagen-induced arthritis (CIA). C57BL/6 and CD11b(-/-) resistant mice were immunized with type II collagen. CD11b(-/-) mice developed arthritis with early onset, high incidence, and sustained severity compared with C57BL/6 mice. We observed a marked leukocyte infiltration, and histological examinations of the arthritic paws from CD11b(-/-) mice revealed that the cartilage was destroyed in association with strong lymphocytic infiltration. The CD11b deficiency led to enhanced Th17-cell differentiation. CD11b(-/-) dendritic cells (DCs) induced much stronger IL-6 production and hence Th17-cell differentiation than wild-type DCs. Treatment of CD11b(-/-) mice after establishment of the Treg/Th17 balance with an anti-IL-6 receptor mAb significantly suppressed the induction of Th17 cells and reduced arthritis severity. Finally, the severe phenotype of arthritis in CD11b(-/-) mice was rescued by adoptive transfer of CD11b(+) DCs. Taken together, our results indicate that the resistance to CIA in C57BL/6 mice is regulated by CD11b via suppression of IL-6 production leading to reduced Th17-cell differentiation. Therefore, CD11b may represent a susceptibility factor for autoimmunity and could be a target for future therapy.

Dendritic cells (DCs) are the most potent antigen presenting cells and possess an incomparable ability to activate and instruct T cells, which makes them one of the cornerstones in the regulation of the cross-talk between innate and adaptive immunity. Therefore, a deep understanding of DC biology lays the foundations to describe and to harness the mechanisms that regulate the development of the adaptive response, with clear implications in a vast array of fields such as the study of autoimmune diseases and the development of new vaccines. However, the great difficulty to obtain large quantities of viable non-activated DCs for experimentation have considerably hindered the progress of DC research. Several strategies have been proposed to overcome these limitations by promoting an increase of DC abundance in vivo, by inducing DC development from DC progenitors in vitro and by generating stable DC lines. In the past years, we have described a method to derive immortalized stable DC lines, named MutuDCs, from the spleens of Mushi1 mice, a transgenic mouse strain that express the simian virus 40 Large T-oncogene in the DCs. The comparison of these DC lines with the vast variety of DC subsets described in vivo has shown that all the MutuDC lines that we have generated so far have phenotypic and functional features of type 1 conventional DCs (cDC1s). With the purpose of deriving DC lines with characteristics of type 2 conventional DCs (cDC2s), we bred a new Batf3 -/- Mushi1 murine line in which the development of the cDC1 subset is severely defective. The new MutuDC line that we generated from Batf3 -/- Mushi1 mice was phenotypically and functionally characterized in this work. Our results demonstrated that all the tested characteristics of this new cell line, including the expression of subset-determining transcription factors, the profile of cytokine production and the ability to present antigens, are comparable with the features of splenic CD4 - cDC2s. Therefore, we concluded that our new cell line, that we named CD4 - MutuDC2 line, represents a valuable model for the CD4 - cDC2 subset.

Dendritic cells (DCs) play a central role in shaping immunogenic as well as tolerogenic adaptive immune responses and thereby dictate the outcome of adaptive immunity. Here, we report the generation of a CD8α(+) DC line constitutively secreting the tolerogenic cytokine interleukin (IL)-35. IL-35 secretion led to impaired CD4(+) and CD8(+) T lymphocyte proliferation and interfered with their function in vitro and also in vivo. IL-35 was furthermore found to induce a tolerogenic phenotype on CD8α(+) DCs, characterized by the upregulation of CD11b, downregulation of MHC class II, a reduced costimulatory potential as well as production of the immunomodulatory molecule IL-10. Vaccination of mice with IL-35-expressing DCs promoted tumor growth and reduced the severity of autoimmune encephalitis not only in a preventive but also after induction of encephalitogenic T cells. The reduction in experimental autoimmune encephalitis severity was significantly more pronounced when antigen-pulsed IL-35(+) DCs were used. These findings suggest a new, indirect effector mechanism by which IL-35-responding antigen-presenting cells contribute to immune tolerance. Furthermore, IL-35-transfected DCs may be a promising approach for immunotherapy in the context of autoimmune diseases.