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Gut-draining mesenteric lymph nodes (mLNs) are important for inducing peripheral tolerance towards food and commensal antigens by providing an optimal microenvironment for de novo generation of Foxp3+ regulatory T cells (Tregs). We previously identified microbiota-imprinted mLN stromal cells as a critical component in tolerance induction. Here we show that this imprinting process already takes place in the neonatal phase, and renders the mLN stromal cell compartment resistant to inflammatory perturbations later in life. LN transplantation and single-cell RNA-seq uncover stably imprinted expression signatures in mLN fibroblastic stromal cells. Subsetting common stromal cells across gut-draining mLNs and skin-draining LNs further refine their location-specific immunomodulatory functions, such as subset-specific expression of Aldh1a2/3. Finally, we demonstrate that mLN stromal cells shape resident dendritic cells to attain high Treg-inducing capacity in a Bmp2-dependent manner. Thus, crosstalk between mLN stromal and resident dendritic cells provides a robust regulatory mechanism for the maintenance of intestinal tolerance.

Since its emergence in December 2019, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has spread globally and become a major public health burden. Despite its close phylogenetic relationship to SARS-CoV, SARS-CoV-2 exhibits increased human-to-human transmission dynamics, likely due to efficient early replication in the upper respiratory epithelium of infected individuals. Since different temperatures encountered in the human upper and lower respiratory tract (37°C and 33°C, respectively) have been shown to affect the replication kinetics of several respiratory viruses, as well as host immune response dynamics, we investigated the impact of temperatures during SARS-CoV-2 and SARS-CoV infection using the primary human airway epithelial cell culture model. SARS-CoV-2, in contrast to SARS-CoV, replicated to higher titers when infections were performed at 33°C rather than 37°C. Although both viruses were highly sensitive to type I and type III interferon pretreatment, a detailed time-resolved transcriptome analysis revealed temperature-dependent interferon and pro-inflammatory responses specifically induced by SARS-CoV or SARS-CoV-2, which amplitude was inversely proportional to their replication efficiencies at 33°C or 37°C. These data provide crucial insight on pivotal virus–host interaction dynamics and are in line with characteristic clinical features of SARS-CoV-2 and SARS-CoV, as well as their respective transmission efficiencies.

Some isolates of Yersinia pseudotuberculosis produce the cytotoxic necrotizing factor (CNFY), but the functional consequences of this toxin for host-pathogen interactions during the infection are unknown. In the present study we show that CNFY has a strong influence on virulence. We demonstrate that the CNFY toxin is thermo-regulated and highly expressed in all colonized lymphatic tissues and organs of orally infected mice. Most strikingly, we found that a cnfY knock-out variant of a naturally toxin-expressing Y. pseudotuberculosis isolate is strongly impaired in its ability to disseminate into the mesenteric lymph nodes, liver and spleen, and has fully lost its lethality. The CNFY toxin contributes significantly to the induction of acute inflammatory responses and to the formation of necrotic areas in infected tissues. The analysis of the host immune response demonstrated that presence of CNFY leads to a strong reduction of professional phagocytes and natural killer cells in particular in the spleen, whereas loss of the toxin allows efficient tissue infiltration of these immune cells and rapid killing of the pathogen. Addition of purified CNFY triggers formation of actin-rich membrane ruffles and filopodia, which correlates with the activation of the Rho GTPases, RhoA, Rac1 and Cdc42. The analysis of type III effector delivery into epithelial and immune cells in vitro and during the course of the infection further demonstrated that CNFY enhances the Yop translocation process and supports a role for the toxin in the suppression of the antibacterial host response. In summary, we highlight the importance of CNFY for pathogenicity by showing that this toxin modulates inflammatory responses, protects the bacteria from attacks of innate immune effectors and enhances the severity of a Yersinia infection.

De novo induction of Foxp3⁺ regulatory T cells (Tregs) is particularly efficient in gut-draining mesenteric and celiac lymph nodes (mLN and celLN). Here we used LN transplantations to dissect the contribution of stromal cells and environmental factors to the high Treg-inducing capacity of these LN. After transplantation into the popliteal fossa, mLN and celLN retained their high Treg-inducing capacity, whereas transplantation of skin-draining LN into the gut mesenteries did not enable efficient Treg induction. However, de novo Treg induction was abolished in the absence of dendritic cells (DC), indicating that this process depends on synergistic contributions of stromal and DC. Stromal cells themselves were influenced by environmental signals as mLN grafts taken from germ-free donors and celLN grafts taken from vitamin A-deficient donors did not show any superior Treg-inducing capacity. Collectively, our observations reveal a hitherto unrecognized role of LN stromal cells for the de novo induction of Foxp3⁺ Tregs.

215 words Main text: 2965 words Abstract The human conductive respiratory tract spans a long anatomical distance and represents an important barrier to constrain invading respiratory pathogens. The disparate ambient temperatures found in the upper and lower respiratory tract have been demonstrated to influence the replication kinetics of common cold viruses as well as the associated host responses. Here, we employed the human airway epithelial cell (hAEC) culture model to investigate the impact of ambient temperatures found in the upper and lower respiratory tract, 33°C and 37°C, respectively, on the viral replication kinetics and host innate immune response dynamics during SARS-CoV-2 and SARS-CoV infections. Strikingly, SARS-CoV-2, in contrast to SARS-CoV, replicated more efficiently at temperatures encountered in the upper respiratory tract, and displayed higher sensitivity to type I and type III IFNs than SARS-CoV. Timeresolved transcriptome analysis highlighted a temperature-dependent induction of IFN-mediated antiviral response, whose amplitude inversely correlated with the replication kinetic efficiencies of both SARS-CoV-2 and SARS-CoV at temperatures found in the upper and lower respiratory tract. Altogether, these data reflect clinical features of SARS-CoV-2 and SARS-CoV and subsequently, their associated human-to-human transmission efficiencies. They provide crucial insights of the profound impact of ambient temperatures on viral replication and associated pivotal virus -host interaction dynamics. This knowledge can be exploited for the development of novel intervention strategies against SARS-CoV-2.

Single-cell RNA-sequencing (scRNA-seq) approaches have transformed our ability to resolve cellular properties across systems, but are currently tailored toward large cell inputs (> 1,000 cells). This renders them inefficient and costly when processing small, individual tissue samples, which tends to be resolved by loading bulk samples, yielding confounded mosaic cell population read-outs. Here, we developed a deterministic, mRNA-capture bead and cell co-encapsulation dropleting system, DisCo, aimed at processing low-input samples (<500 cells). We demonstrate that DisCo enables precise particle and cell positioning and droplet sorting control through combined machine-vision and multilayer microfluidics, enabling continuous processing of lowinput single cell suspensions at high capture efficiency (> 70%) and speeds up to 350 cells per hour. To underscore DisCo's unique capabilities, we analyzed 31 individual intestinal organoids at varying developmental stages. This revealed extensive organoid heterogeneity, identifying distinct subtypes including i) a regenerative fetal-like Ly6a + stem cell population which persists as symmetrical cysts, or spheroids, even under differentiation conditions, and ii) a so far uncharacterized "gobloid" subtype consisting predominantly of precursor and mature (Muc2 + ) goblet cells. To complement this dataset and to demonstrate DisCo's capacity to process lowinput, in vivo-derived tissues, we also analyzed individual mouse intestinal crypts. This revealed the existence of crypts with compositional similarity to spheroids, i.e. predominantly consisting of regenerative stem cells, suggesting the existence of regenerating crypts in the homeostatic intestine. These findings demonstrate the unique power of DisCo in providing high-resolution snapshots of cellular heterogeneity among small, individual tissues.

Activated naive CD4+ T cells are highly plastic cells that can differentiate into various T helper (Th) cell fates characterized by the expression of effector cytokines like IFN-γ (Th1), IL-4 (Th2) or IL-17A (Th17). Although previous studies have demonstrated that epigenetic mechanisms including DNA demethylation can stabilize effector cytokine expression, a comprehensive analysis of the changes in the DNA methylation pattern during differentiation of naive T cells into Th cell subsets is lacking. Hence, we here performed a genome-wide methylome analysis of ex vivo isolated naive CD4+ T cells, Th1 and Th17 cells. We could demonstrate that naive CD4+ T cells share more demethylated regions with Th17 cells when compared to Th1 cells, and that overall Th17 cells display the highest number of demethylated regions, findings which are in line with the previously reported plasticity of Th17 cells. We could identify seven regions located in Il17a, Zfp362, Ccr6, Acsbg1, Dpp4, Rora and Dclk1 showing pronounced demethylation selectively in ex vivo isolated Th17 cells when compared to other ex vivo isolated Th cell subsets and in vitro generated Th17 cells, suggesting that this unique epigenetic signature allows identifying and functionally characterizing in vivo generated Th17 cells.