A Subset of Type I Conventional Dendritic Cells Controls Cutaneous Bacterial Infections through VEGFα-Mediated Recruitment of Neutrophils

Skin conventional dendritic cells (cDCs) exist as two distinct subsets, cDC1s and cDC2s, which maintain the balance of immunity to pathogens and tolerance to self and microbiota. Here, we examined the roles of dermal cDC1s and cDC2s during bacterial infection, notably Propionibacterium acnes (P. acnes). cDC1s, but not cDC2s, regulated the magnitude of the immune response to P. acnes in the murine dermis by controlling neutrophil recruitment to the inflamed site and survival and function therein. Single-cell mRNA sequencing revealed that this regulation relied on secretion of the cytokine vascular endothelial growth factor α (VEGF-α) by a minor subset of activated EpCAM+CD59+Ly-6D+ cDC1s. Neutrophil recruitment by dermal cDC1s was also observed during S. aureus, bacillus Calmette-Guérin (BCG), or E. coli infection, as well as in a model of bacterial insult in human skin. Thus, skin cDC1s are essential regulators of the innate response in cutaneous immunity and have roles beyond classical antigen presentation.

Protective role of conventional dendritic cells in experimental model of sepsis

Sepsis is a serious medical condition caused by an overwhelming immune response to infection and is a major challenge in the intensive care unit, where it’s one of the leading causes of death. Dendritic cells (DCs), acting as sentinels, constantly sense and respond to environmental stimuli. During the progression of sepsis, DCs have been reported to take part in the aberrant immune response and be necessary for survival. Recently, we demonstrated that activation of Aryl Hydrocarbon receptor (AhR), by tryptophan metabolites in DCs, represents a protective mechanism in an experimental animal model of Lipopolysaccharide (LPS)-induced septic shock. Based on these results we examined the role of DCs subsets in sepsis. To determine whether DCs are required for protection against LPS sterile septic shock we used Zbtb46DTR mouse model. We found that Zbtb46DTR chimeras treated with diphtheria toxin are unable to survive after sub-lethal LPS challenge compared to wild-type mice reconstituted with wild-type bone marrow. In addition, naive mice intravenously transferred with LPS-treated DCs survived to a lethal LPS challenge. Notably, we found that mice lacking of CD24+ DCs are extremely susceptible to LPS. Moreover, LPS selectively induces indoleamine-2,3-dioxygenase 1 (IDO1) in bone marrow-derived CD24+. Our data demonstrate for the first time that DCs and specifically CD24+ DCs, play a critical role in sepsis protection.

Deciphering Interleukin 4-induced gene-1 as novel immune regulatory pathway in dendritic cell subsets

Interleukin 4-induced gene-1 (IL4i1) is as L-phenylalanine oxidase initially described as an early IL-4-inducible gene in B cells [1]. Herein, we analyzed IL4I1 expression in different DC subsets and investigated the possible role of IL4I1 in T-cell regulation. By using a novel and highly specific antibody, reactive to mouse IL4I1, developed in our laboratory, we found that IL4i1 could be induced by IL-4 or CpG olognucleotides (CpGODN) only in classical DCs (cDC). IL4i1 induction, by IL-4 was prevented in cDCs isolated from AhR−/− mice. Moreover, IL-4–treated cDCs cultured with CD4+T cells favored the expansion of FoxP3+ CD4+ T cells (Treg) compared to untreated cDCs. This effect was abrogated in the presence of a small interfering RNA (siRNA) targeting IL4i1 but not by a control siRNA. Notably, IL-4-induced IL4i1 expression in cDCs required aryl hydrocarbon receptor (AhR) in these cells. IL4I1-mediated oxidative deamination of phenylalanine produces H2O2 and phenylpyruvate (PP). Recently we found that PP is a novel ligand of AhR. Phenylpyruvate administration in vivo significantly reduced disease severity in a murine model of multiple sclerosis, such effect was prevented in AhR−/− mice. Overall, these results point IL4i1 as a key enzyme in the regulation of immune responses.

Rab43 facilitates cross-presentation of cell-associated antigens by CD8a+ dendritic cells

Batf3-dependent classical dendritic cells (cDCs) are essential for cross-presentation and clearance of intracellular pathogens through priming of CD8 T cells. By analyzing differences in gene expression between cDC subsets we identified vesicular transport molecules unique to cross-presenting dendritic cell subsets. RAB43, a GTPase that is localized to the golgi, is selectively expressed in Batf3-dependent CD8a+ and CD103+ cDCs and was highly conserved between mouse and human. Mice with germline and conditional Rab43 deletions are viable and fertile with normal hematopoiesis. However, mice lacking Rab43 showed reduced cross-presentation of cell-associated, but not soluble, antigens both in vitro and in vivo. Bone-marrow derived DCs (BMDCs) from Rab43 deficient mice show normal cross-presentation efficiency, suggesting that Rab43 is involved in optimizing cross-presentation in vivo through a pathway unique to CD8a+ DCs.