Barbara Ursula Schraml

Maintaining a balanced immunity between pathogen defense and tolerance to environmental antigens in neonates is essential for survival and the establishment of life-long immune homeostasis. Instructed by environmental signals, type 1 conventional dendritic cells (cDC1) contribute to both processes but how the balance may be achieved is unclear. Here, we uncover an interferon (IFN)γ-driven regulatory circuit in early life that relays dietary cues to spleen cDC1. IFNγ-mediated STAT1-signaling induces an immunogenic maturation program in spleen cDC1 that enables them to shape the effector differentiation of antigen-experienced effector memory CD8⁺ T cells. This cDC1 program emerges during the transition from breastfeeding to solid food at weaning, occurs in germ-free mice, and remains operative to dietary intervention in adult mice. At weaning, this IFNγ signal enables spleen cDC1 to shape the effector phenotype of food-antigen-specific CD8 ⁺ T cells in a feedforward manner, thereby recalibrating the developing T cell pool. Our findings identify diet as a modifiable cue that can tune systemic cDC1-mediated immunity, opening new opportunities to steer immune responses during early life and beyond.

Type 2 conventional dendritic cells (cDC2) orchestrate T cell immunity, yet the signals that regulate their tissue-specific functions across development remain poorly defined. We demonstrate that splenic cDC2/DC3 subset heterogeneity is established perinatally and that splenic ESAM ^hi cDC2A undergo a transcriptional and functional transition around the time of weaning, which occurs independently of microbiota. Comparative transcriptomics identified neonatal-specific regulatory programs, including elevated expression of Plaur , encoding CD87/uPAR. CD87 sensitizes neonatal ESAM ^hi cDC2A to coagulation factor XII (FXII), thereby enhancing their capacity to promote Th17 differentiation. In human infants, CD87 expression was high on cDC2, its expression declined with age and in plasma of preterm infants CD87 positively correlated with Th17-associated cytokines. Together, we identify a conserved link between coagulation pathways and cDC2 developmental programming that may offer new opportunities to modulate Th17 responses in infancy. Summary: Splenic cDC2 undergo a transcriptional and functional remodeling around weaning. Elevated CD87 expression on neonatal cDC2 enhances their FXII-driven Th17 potential. Conserved in human infants, elevated CD87 expression reveals a coagulation-linked pathway shaping early-life dendritic cell function and suggests targets to improve vaccination.

Balancing pathogen defence with maintaining tolerance to environmental antigens, such as food or commensals, in neonates is essential for survival and the establishment of life-long immune homeostasis. Instructed by environmental signals type 1 conventional dendritic cells (cDC1) drive either T cell tolerance or immunity. Here, we uncover an interferon (IFN)-γ-driven regulatory circuit in early life that relays dietary cues to spleen cDC1. Loss-of-function demonstrates that IFNγ-mediated STAT1-signaling induces an immunogenic maturation program in spleen cDC1 that instructs cDC1 to expand effector memory CD8⁺ T cells. This program emerges during weaning, when IFNγ production from lymphocytes rises, it occurs in germ-free mice and remains responsive to dietary intervention in adult mice. During the transition from breastfeeding to solid food at weaning, this circuit relays dietary information to spleen cDC1 to shape the effector phenotype of food-antigen specific CD8+ T cells in a feed-forward manner, allowing cDC1 to recalibrate the T cell pool at the moment of nutritional independence.

Environmental factors are often detrimental; however, certain environments enhance immune resilience. Notably, children raised on traditional farms show reduced allergies and asthma prevalence. Here, we investigated how a beneficial environment, using farm dust (FD) extract, influenced lung immune function in ovalbumin-induced allergic inflammation. FD exposure reduced allergic lung inflammation and increased monocyte-derived macrophage (MDM) recruitment. Single-cell RNA sequencing revealed that FD-exposed MDMs had altered gene expression, including dampened Ccl8 and major histocompatibility complex class II expression, impairing eosinophil recruitment and antigen presentation. RNA sequencing and assay for transposase-accessible chromatin using sequencing confirmed FD-induced epigenetic reprogramming ex vivo, on bone marrow–derived macrophages. This modulation, seen in both human and murine cells, relied on histone deacetylase activity sustained by peroxisome proliferator–activated receptor γ signaling. These findings suggest that beneficial environmental exposures can reprogram immune cells and may offer a previously unidentified strategy for asthma prevention.

BioStudies – one package for all the data supporting a study

BioStudies – one package for all the data supporting a study

Conventional dendritic cells (cDCs) are potent antigen-presenting cells (APCs) that integrate signals from their environment allowing them to direct situation-adapted immunity. Thereby they harbor great potential for being targeted in vaccination, autoimmunity, and cancer. Here, we use fate mapping, functional analyses, and comparative cross-species transcriptomics to show that RORγt ⁺ DCs are a conserved, functionally versatile, and transcriptionally distinct type of DCs. RORγt ⁺ DCs entail various populations described in different contexts including Janus cells/RORγt-expressing extrathymic Aire-expressing cells (eTACs), subtypes of Thetis cells, RORγt ⁺ -DC (R-DC) like cells, cDC2C and ACY3 ⁺ DCs. We show that in response to inflammatory triggers, RORγt ⁺ DCs can migrate to lymph nodes and in the spleen can activate naïve CD4 ⁺ T cells. These findings expand the functional repertoire of RORγt ⁺ DCs beyond the known role of eTACs and Thetis cells in inducing T cell tolerance to self-antigens and intestinal microbes in mice. We further show that RORγt ⁺ DCs with proinflammatory features accumulate in autoimmune neuroinflammation in mice and men. Thus, our work establishes RORγt ⁺ DCs as immune sentinel cells that exhibit a broad functional spectrum ranging from inducing peripheral T cell tolerance to T cell activation depending on signals they integrate from their environment.

Chronic inflammation in inflammatory bowel disease (IBD) patients represents a risk factor for developing colitis-associated cancer (CAC). We previously linked the endoplasmic reticulum unfolded protein response (UPRER) signal transducer activating transcription factor 6 (ATF6) with spontaneous microbiota-dependent colonic adenoma development in mice expressing epithelial-specific activated ATF6 (nATF6IEC). To investigate IBD-related risk factors in ATF6-mediated tumorigenesis, we crossed tumor-free monoallelic (tg/wt) nATF6IEC mice with Interleukin-10 deficient mice (Il10-/-). IL10 deficiency initiated tumor susceptibility, with 77% of 12-week tg/wt;Il10-/- mice developing colonic adenomas and invasive carcinomas in this novel CAC mouse model. Tumor formation correlated with mucosal immune cell infiltration, characterized by CD11b+ granulocytes and monocytes, and mucosa-associated dysbiosis. Colonization of germ-free nATF6IEC;Il10-/- mice with minimal biosynthetic consortia and IBD stool re-established CAC, confirming microbiota-dependent ATF6-driven tumorigenesis. Increased ATF6 expression in IBD patients during active disease highlights its human relevance. Our findings show that IBD susceptibility heightens the risk for ATF6-driven tumorigenesis.

Conventional dendritic cells (cDCs) are potent antigen presenting cells (APCs) that exhibit tissue and age-specific diversity allowing them to direct situation-adapted immunity. Thereby they harbor great potential for being targeted in vaccination and cancer. Here, we resolve conflicting data about expression of retinoic acid receptor-related orphan receptor-γt (RORψt) in cDCs. We show that RORψt ⁺ DCs exist in murine lymphoid and non-lymphoid tissues across age. Fate mapping, functional assays and single cell multiomic profiling reveal these cells as ontogenetically and transcriptionally distinct from other well characterized cDC subtypes, as well as from RORψt ⁺ type 3 innate lymphocytes (ILC3s). We show that RORψt ⁺ DCs can migrate to lymph nodes and activate naïve CD4 ⁺ T cells in response to inflammatory triggers. Comparative and cross-species transcriptomics revealed homologous populations in human spleen, lymph nodes and intestines. Further, integrated meta-analyses aligned RORψt ⁺ DCs identified here with other emerging populations of RORψt ⁺ APCs, including R-DC-like cells, Janus cells/extrathymic Aire expressing cells (eTACs) and subtypes of Thetis cells. While RORψt ⁺ APCs have primarily been linked to T cell tolerance, our work establishes RORψt ⁺ DCs as unique lineage of immune sentinel cells conserved across tissues and species that expands the functional repertoire of RORψt ⁺ APCs beyond promoting tolerance. One sentence summary: RORγt ⁺ DC exhibit versatile APC functions and are a distinct immune lineage conserved across age, tissues and species that entails Thetis cells, Janus cells/RORγt ⁺ eTACs and R-DC-like cells.

Conventional dendritic cells (cDC) play key roles in immune induction, but what drives their heterogeneity and functional specialization is still ill-defined. Here we show that cDC-specific deletion of the transcriptional repressor Bcl6 in mice alters the phenotype and transcriptome of cDC1 and cDC2, while their lineage identity is preserved. Bcl6-deficient cDC1 are diminished in the periphery but maintain their ability to cross-present antigen to CD8⁺ T cells, confirming general maintenance of this subset. Surprisingly, the absence of Bcl6 in cDC causes a complete loss of Notch2-dependent cDC2 in the spleen and intestinal lamina propria. DC-targeted Bcl6-deficient mice induced fewer T follicular helper cells despite a profound impact on T follicular regulatory cells in response to immunization and mounted diminished Th17 immunity to Citrobacter rodentium in the colon. Our findings establish Bcl6 as an essential transcription factor for subsets of cDC and add to our understanding of the transcriptional landscape underlying cDC heterogeneity.