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Live cells are the most abundant sources of antigen in a tumor-bearing host. Here, we used live tumor cells as source of antigens to investigate the mechanism underlying their immunogenicity in murine tumor models. The live tumor cells were significantly more immunogenic than irradiated or apoptotic tumor cells. We examined the interaction of live and apoptotic tumor cells with major subsets of antigen-presenting cells, i.e., CD8α+ dendritic cells (DC), CD8α− DCs, plasmacytoid DCs, and CD169+ macrophages at skin draining lymph nodes. The CD8α+ DCs captured cell-associated antigens from both live and apoptotic tumor cells, whereas CD169+ macrophages picked up cell-associated antigens mostly from apoptotic tumor cells. Trogocytosis and cross-dressing of membrane-associated antigenic material from live tumor cells to CD8α+ DCs was the primary mechanism for cross-priming of tumor antigens upon immunization with live cells. Phagocytosis of apoptotic tumor cells was the primary mechanism for cross-priming of tumor antigens upon immunization with apoptotic or irradiated cells. These findings clarify the mechanism of cross-priming of cancer antigens by DCs, allowing for a greater understanding of antitumor immune responses.

Our previous studies identified a population of stem cell-like proliferating myeloid cells within inflamed tissues that could serve as a reservoir for tissue macrophages to adopt different activation states depending on the microenvironment. By lineage tracing cells derived from CX3CR1+precursors in mice during infection and profiling by scRNA-seq, here we identify a cluster of BIRC5+myeloid cells that expanded in the liver during either chronic infection with the parasiteSchistosoma mansonior the bacterial pathogenStaphylococcus aureus. In the absence of tissue damaging toxins,S. aureusinfection does not elicit these BIRC5+cells. Moreover, deletion of BIRC5 from CX3CR1 expressing cells results in improved survival duringS. aureusinfection. Hence, the combination of scRNA-Seq and genetic fate mapping CX3CR1+cells revealed a toxin dependent pathogenic role for BIRC5 in myeloid cells duringS. aureusinfection.

Small animal models have been a challenge for the study of SARS-CoV-2 transmission, with most investigators using golden hamsters or ferrets1, 2. Mice have the advantages of low cost, wide availability, less regulatory and husbandry challenges, and the existence of a versatile reagent and genetic toolbox. However, adult mice do not robustly transmit SARS-CoV-23. Here we establish a model based on neonatal mice that allows for transmission of clinical SARS-CoV-2 isolates. We characterize tropism, respiratory tract replication and transmission of ancestral WA-1 compared to variants Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), Delta (B.1.617.2), Omicron BA.1 and Omicron BQ.1.1. We identify inter-variant differences in timing and magnitude of infectious particle shedding from index mice, both of which shape transmission to contact mice. Furthermore, we characterize two recombinant SARS-CoV-2 lacking either the ORF6 or ORF8 host antagonists. The removal of ORF8 shifts viral replication towards the lower respiratory tract, resulting in significantly delayed and reduced transmission in our model. Our results demonstrate the potential of our neonatal mouse model to characterize viral and host determinants of SARS-CoV-2 transmission, while revealing for the first time a role for an accessory protein in this context.

Genetically Engineered Mouse Models (GEMMs) aid in understanding human pathologies and developing new therapeutics, yet recapitulating human diseases authentically in mice is challenging to design and execute. Advances in genomics have highlighted the importance of non-coding regulatory genome sequences controlling spatiotemporal gene expression patterns and splicing to human diseases. It is thus apparent that including regulatory genomic regions during the engineering of GEMMs is highly preferable for disease modeling, with the prerequisite of large-scale genome engineering ability. Existing genome engineering methods have limits on the size and efficiency of DNA delivery, hampering routine creation of highly informative GEMMs. Here, we describe mSwAP-In (mammalian Switching Antibiotic resistance markers Progressively for Integration), a method for efficient genome rewriting in mouse embryonic stem cells. We first demonstrated the use of mSwAP-In for iterative genome rewriting of up to 115 kb of the Trp53 locus, as well as for genomic humanization of up to 180 kb ACE2 locus in response to the COVID-19 pandemic. Second, we showed the hACE2 GEMM authentically recapitulated human ACE2 expression patterns and splicing, and importantly, presented milder symptoms without mortality when challenged with SARS-CoV-2 compared to the K18-ACE2 model, thus representing a more authentic model of infection.

Chikungunya virus (CHIKV) infection has been associated with severe cardiac manifestations, yet, how CHIKV infection leads to heart disease remains unknown. Here, we leveraged both mouse models and human primary cells to define the mechanisms of CHIKV heart infection. We found that CHIKV actively replicates in cardiac fibroblasts and is cleared without significant tissue damage through the induction of a local type-I interferon response from both infected and non-infected cardiac cells. Importantly, signaling through the mitochondrial antiviral-signaling protein (MAVS) is required for viral clearance from the heart. In the absence of MAVS, persistent infection leads to focal myocarditis and major vessel vasculitis persisting for up to 60 days post-infection, suggesting CHIKV can lead to vascular inflammation and potential long-lasting cardiovascular complications. This study provides a model of CHIKV cardiac infection and mechanistic insight into CHIKV-induced heart disease, underscoring the importance of monitoring cardiac function in patients with CHIKV infections.

While the standard regimen of the BNT162b2 mRNA vaccine for SARS-CoV-2 includes two doses administered 3 weeks apart, some public health authorities are spacing these doses, raising concerns about efficacy. However, data indicate that a single dose can be up to 90% effective starting 14 days post-administration. To assess the mechanisms contributing to protection, we analyzed humoral and T cell responses three weeks after a single BNT162b2 dose. We observed weak neutralizing activity elicited in SARS-CoV-2 naive individuals but strong anti-receptor binding domain and spike antibodies with Fc-mediated effector functions and cellular CD4

Live cells are the most abundant sources of antigen in a tumor-bearing host. Here, we used live tumor cells as source of antigens to investigate the mechanism underlying their immunogenicity in murine tumor models. The live tumor cells were significantly more immunogenic than irradiated or apoptotic tumor cells. We examined the interaction of live and apoptotic tumor cells with major subsets of antigen-presenting cells, i.e., CD8α+ dendritic cells (DC), CD8α− DCs, plasmacytoid DCs, and CD169+ macrophages at skin draining lymph nodes. The CD8α+ DCs captured cell-associated antigens from both live and apoptotic tumor cells, whereas CD169+ macrophages picked up cell-associated antigens mostly from apoptotic tumor cells. Trogocytosis and cross-dressing of membrane-associated antigenic material from live tumor cells to CD8α+ DCs was the primary mechanism for cross-priming of tumor antigens upon immunization with live cells. Phagocytosis of apoptotic tumor cells was the primary mechanism for cross-priming of tumor antigens upon immunization with apoptotic or irradiated cells. These findings clarify the mechanism of cross-priming of cancer antigens by DCs, allowing for a greater understanding of antitumor immune responses.

Increasing age is the strongest predictor of risk of COVID-19 severity. Unregulated cytokine storm together with impaired immunometabolic response leads to highest mortality in elderly infected with SARS-CoV-2. To investigate how aging compromises defense against COVID-19, we developed a model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain MHV-A59 (mCoV-A59) that recapitulated majority of clinical hallmarks of COVID-19. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Ketogenic diet increases beta-hydroxybutyrate, expands tissue protective γδ T cells, deactivates the inflammasome and decreases pathogenic monocytes in lungs of infected aged mice. These data underscore the value of mCoV-A59 model to test mechanism and establishes harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against COVID-19 in the elderly.- Natural MHV-A59 mouse coronavirus infection mimics COVID-19 in elderly.- Aged infected mice have systemic inflammation and inflammasome activation.- Murine beta coronavirus (mCoV) infection results in loss of pulmonary γδ T cells.- Ketones protect aged mice from infection by reducing inflammation.Elderly have the greatest risk of death from COVID-19. Here, Ryu et al report an aging mouse model of coronavirus infection that recapitulates clinical hallmarks of COVID-19 seen in elderly. The increased severity of infection in aged animals involved increased inflammasome activation and loss of γδ T cells that was corrected by ketogenic diet.

RATIONALE:Secondary infections with bacterial pathogens are thought to be responsible for poor outcomes in the 1918 Spanish and H1N1 pandemics. We postulate that poor prognosis in patients with SARS-CoV2 may be associated with uncontrollable viral replication, co-infection with a secondary pathogen, and over exuberant host immune response. We seek to evaluate whether there is an association between distinct features of the lower airway microbiota and poor clinical outcome in patients with SARS-CoV2. METHODS:We collected lower airway samples in 148 patients from NYU admitted between 3/10/2020 and 5/10/2020 with severe respiratory failure requiring mechanical ventilation and that underwent bronchoscopy for airway clearance and/or tracheostomy. Clinical outcome was defined as dead vs alive. DNA was isolated in parallel using zymoBIOMICS™ DNA/RNA Miniprep Kit (Cat: R2002) as per manufacturer's instructions. The V4 region of the 16S rRNA gene marker was sequenced using Illumina MiSeq. Sequences were analyzed using the Quantitative Insights into Microbial Ecology (QIIME version 1.9.1) pipeline. Total bacterial load was evaluated in lower airway samples using digital droplet PCR targeting the 16S rRNA gene. RESULTS:Of the 148 patients included, 114 survived (77%) and 34 (23%) died. Among those with poor clinical outcome, there was a non-statistically significant trend towards higher age and BMI. Patients who died more commonly had chronic kidney disease and prior cerebrovascular accidents, and more often required dialysis. There was no statistically significant difference in the rate of positive bacterial respiratory or blood cultures among those that survived vs. those that died (75 vs. 73% and 43 vs 38%, respectively). Topographical analysis of the 16S RNA microbiome shows compositional differences between the upper and lower airways based on β diversity comparisons. When comparing across clinical outcomes, the α diversity was lower in the dead group but there was no statistically significant difference in overall community composition (β diversity). Taxonomic differential enrichment analysis using DESeq analysis showed that oral commensals were enriched in the group that survived. Patients that died had a higher bacterial load in their lower airways than those who survived. CONCLUSION:Using samples obtained via bronchoscopy we identified lower airway microbiota signatures associated with mortality among critical patients infected with SARS-CoV2. Taxonomic signals identified as associated with poor prognosis did not reveal bacterial taxa commonly classified as respiratory pathogens. This data is not supportive of the hypothesis that secondary untreated bacterial co-infections are responsible for increased mortality in patients with severe SARS-CoV-2.

The response to systemic infection and injury requires the rapid adaptation of hematopoietic stem cells (HSCs), which proliferate and divert their differentiation toward the myeloid lineage. Significant interest has emerged in understanding the signals that trigger the emergency hematopoietic program. However, the mechanisms that halt this response of HSCs, which is critical to restore homeostasis, remain unknown. Here we reveal that the E3 ubiquitin ligase Speckle-type BTB–POZ protein (SPOP) restrains the inflammatory activation of HSCs. In the absence of Spop, systemic inflammation proceeded in an unresolved manner, and the sustained response in the HSCs resulted in a lethal phenotype reminiscent of hyper-inflammatory syndrome or sepsis. Our proteomic studies decipher that SPOP restricted inflammation by ubiquitinating the innate signal transducer myeloid differentiation primary response protein 88 (MYD88). These findings unearth an HSC-intrinsic post-translational mechanism that is essential for reestablishing homeostasis after emergency hematopoiesis.

Purpose The purpose of this paper is to present an organized review of existing research on reconfigurable manufacturing system (RMS). The paper considers majority of the prominent research articles in the domain of RMS published ever since RMS was envisaged in 1997. Design/methodology/approach The paper systematically reviews, classifies and analyses the published literature on postulations and design of RMSs. The general observations from the literature and research gaps recognized thereon are highlighted at the end of each section/sub-section. Findings The paper reveals important aspects related to RMS research since its inception. It also recognizes the areas of RMS research requiring more focus. The study also highlights open issues and future directions for further research. Practical implications The literature in the domain of RMS has so far been narrow. This paper reviews the prominent research in this field and presents an overview of its conceptual developments and various mathematical models for the RMS design and its optimization so far developed by the researchers. Further, manufacturing advancements and future directions have also been proposed for the efficient execution of RMS paradigm in manufacturing industries. Originality/value The paper provides an organized listing of published research work in the field of RMS. This work will provide an insight to the researchers, practitioners and others related directly or indirectly to this field to develop and understand better strategies for supervising and controlling the smooth implementation of RMS.

The COVID19 pandemic caused by SARS CoV 2 remains a global health crisis even with vaccines and sparse FDA approved therapies. To limit mortality and morbidity, therapeutics are critical. Galectin 9 (gal9) is a b-galactoside binding protein, modulating cell-cell and cell-matrix interactions. It has been shown circulating gal9 levels are elevated in response to infection in patient sera with moderate to severe disease. One report gal9 unexpectedly competitively binds the ACE2 receptor on host cells, impeding viral entry. Therefore, we hypothesize early recombinant gal9 (rgal9) treatment post infection (pi) may prevent binding of the virus to prone host cells yielding a decreased severity of SARS CoV 2 related disease. To determine the potential of gal9 for treating COVID19, we infected and treated K18 hACE2 mice with a single dose of human rgal9 (rhgal9) or PBS i.p. and monitored 12 days for morbidity. Subgroups of mice were humanely euthanized at 2 and 5 dpi for viral plaque assay, flow cytometry, and protein analysis from lung tissue and BALF. We found that mice treated with rhgal9 during acute phase of infection have improved survival compared to PBS control. At 5 dpi, rhgal9 mice had enhanced viral clearance in the BALF and not in the lung parenchyma. We noted increased CD8 T cell and decreased neutrophil frequencies in the lung at 5 dpi. Finally, BALF had elevated levels of Type 1 IFN at 2 dpi and increased proinflammatory cytokines at 5 dpi. This suggests rhgal9 treatment may be therapeutic for acute COVID19, as rhgal9 with other anti-inflammatory mediator treatments cut associated harmful inflammation. Further studies are required to determine the optimal time, combination and duration of treatment pi to effectively target the gal9 pathway.

Mortality among patients with COVID-19 and respiratory failure is high and there are no known lower airway biomarkers that predict clinical outcome. We investigated whether bacterial respiratory infections and viral load were associated with poor clinical outcome and host immune tone. We obtained bacterial and fungal culture data from 589 critically ill subjects with COVID-19 requiring mechanical ventilation. On a subset of the subjects that underwent bronchoscopy, we also quantified SARS-CoV-2 viral load, analyzed the microbiome of the lower airways by metagenome and metatranscriptome analyses and profiled the host immune response. We found that isolation of a hospital-acquired respiratory pathogen was not associated with fatal outcome. However, poor clinical outcome was associated with enrichment of the lower airway microbiota with an oral commensal (Mycoplasma salivarium), while high SARS-CoV-2 viral burden, poor anti-SARS-CoV-2 antibody response, together with a unique host transcriptome profile of the lower airways were most predictive of mortality. Collectively, these data support the hypothesis that 1) the extent of viral infectivity drives mortality in severe COVID-19, and therefore 2) clinical management strategies targeting viral replication and host responses to SARS-CoV-2 should be prioritized.

Macrophages are known to mediate anti-helminth responses, but it remains uncertain which subsets are involved or how macrophages actually kill helminths. Here we show rapid monocyte recruitment to the lung after infection with the nematode parasite,Nippostrongylus brasiliensis. In this inflamed tissue microenvironment these monocytes differentiate into an alveolar-like macrophage (AM) phenotype, expressing both Siglec-F and CD11c, surround invading parasitic larvae and preferentially kill parasites in vitro. Monocyte-derived AMs (Mo-AMs) express type 2-associated markers and show distinct remodeling of the chromatin landscape relative to tissue-derived AMs. In particular, they express high amounts of Arg1 (arginase-1), which we demonstrate mediates helminth killing through L-arginine depletion. These studies indicate that recruited monocytes are selectively programmed in the pulmonary environment to express AM markers and an anti-helminth phenotype.

SUMMARYIncreasing age is the strongest predictor of risk of COVID-19 severity. Unregulated cytokine storm together with impaired immunometabolic response leads to highest mortality in elderly infected with SARS-CoV-2. To investigate how aging compromises defense against COVID-19, we developed a model of natural murine beta coronavirus (mCoV) infection with mouse hepatitis virus strain MHV-A59 (mCoV-A59) that recapitulated majority of clinical hallmarks of COVID-19. Aged mCoV-A59-infected mice have increased mortality and higher systemic inflammation in the heart, adipose tissue and hypothalamus, including neutrophilia and loss of γδ T cells in lungs. Ketogenic diet increases beta-hydroxybutyrate, expands tissue protective γδ T cells, deactivates the inflammasome and decreases pathogenic monocytes in lungs of infected aged mice. These data underscore the value of mCoV-A59 model to test mechanism and establishes harnessing of the ketogenic immunometabolic checkpoint as a potential treatment against COVID-19 in the elderly.Highlights-Natural MHV-A59 mouse coronavirus infection mimics COVID-19 in elderly.-Aged infected mice have systemic inflammation and inflammasome activation-Murine beta coronavirus (mCoV) infection results in loss of pulmonary γδ T cells.-Ketones protect aged mice from infection by reducing inflammation.eTOC BlurbElderly have the greatest risk of death from COVID-19. Here, Ryu et al report an aging mouse model of coronavirus infection that recapitulates clinical hallmarks of COVID-19 seen in elderly. The increased severity of infection in aged animals involved increased inflammasome activation and loss of γδ T cells that was corrected by ketogenic diet.

While immune responses have been rigorously examined after intravenous Listeria monocytogenes (Lm) infection, less is understood about its dissemination from the intestines or the induction of adaptive immunity after more physiologic models of foodborne infection. Consequently, this study focused on early events in the intestinal mucosa and draining mesenteric lymph nodes (MLN) using foodborne infection of mice with Lm modified to invade murine intestinal epithelium (InlAM Lm). InlAM Lm trafficked intracellularly from the intestines to the MLN and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this, InlAM Lm initially disseminated from the gut to the MLN normally in Batf3–/– mice. Activated migratory DC accumulated in the MLN by 3 days post-infection and surrounded foci of InlAM Lm. At this time Batf3–/– mice displayed reduced InlAM Lm burdens, implicating cDC1 in maximal bacterial accumulation in the MLN. Batf3–/– mice also exhibited profound defects in the induction and gut-homing of InlAM Lm-specific effector CD8 T cells. Restoration of pathogen burden did not rescue antigen-specific CD8 T cell responses in Batf3–/– mice, indicating a critical role for Batf3 in generating anti-InlAM Lm immunity following foodborne infection. Collectively, these data suggest that DC play diverse, dynamic roles in the early events following foodborne InlAM Lm infection and in driving the establishment of intestinal Lm-specific effector T cells. Fil: Imperato, Jessica Nancy. Stony Brook University Renaissance School Of Medicine; Estados Unidos Fil: Xu, Daqi. Uconn Health; Estados Unidos Fil: Romagnoli, Pablo Alberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Grupo Vinculado Centro de Investigacion En Medicina Traslacional Severo R. Amuchastegui - Cimetsa | Universidad Nacional de Cordoba. Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Grupo Vinculado Centro de Investigacion En Medicina Traslacional Severo R. Amuchastegui - Cimetsa | Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Instituto de Investigacion Medica Mercedes y Martin Ferreyra. Grupo Vinculado Centro de Investigacion En Medicina Traslacional Severo R. Amuchastegui - Cimetsa.; Argentina Fil: Qiu, Zhijuan. Stony Brook University Renaissance School Of Medicine; Estados Unidos Fil: Perez, Pedro. Stony Brook University Renaissance School Of Medicine; Estados Unidos Fil: Khairallah, Camille. Stony Brook University Renaissance School Of Medicine; Estados Unidos Fil: Pham, Quynh Mai. Uconn Health; Estados Unidos Fil: Andrusaite, Anna. University of Glasgow; Reino Unido Fil: Bravo Blas, Alberto. The Beatson Institute For Cancer Research; Reino Unido Fil: Milling, Simon W. F.. University of Glasgow; Reino Unido Fil: Lefrancois, Leo. Uconn Health; Estados Unidos Fil: Khanna, Kamal M.. University of New York; Estados Unidos Fil: Puddington, Lynn. Uconn Health; Estados Unidos Fil: Sheridan, Brian S.. Stony Brook University Renaissance School Of Medicine; Estados Unidos

Classic major histocompatibility complex class I (MHC-I) presentation relies on shuttling cytosolic peptides into the endoplasmic reticulum (ER) by the transporter associated with antigen processing (TAP). Viruses disable TAP to block MHC-I presentation and evade cytotoxic CD8+ T cells. Priming CD8+ T cells against these viruses is thought to rely solely on cross-presentation by uninfected TAP-functional dendritic cells. We found that protective CD8+ T cells could be mobilized during viral infection even when TAP was absent in all hematopoietic cells. TAP blockade depleted the endosomal recycling compartment of MHC-I molecules and, as such, impaired Toll-like receptor-regulated cross-presentation. Instead, MHC-I molecules accumulated in the ER-Golgi intermediate compartment (ERGIC), sequestered away from Toll-like receptor control, and coopted ER-SNARE Sec22b-mediated vesicular traffic to intersect with internalized antigen and rescue cross-presentation. Thus, when classic MHC-I presentation and endosomal recycling compartment-dependent cross-presentation are impaired in dendritic cells, cell-autonomous noncanonical cross-presentation relying on ERGIC-derived MHC-I counters TAP dysfunction to nevertheless mediate CD8+ T cell priming.

Live cells are the most abundant sources of antigen in a tumor-bearing host. Here, we used live tumor cells as source of antigens to investigate the mechanism underlying their immunogenicity in murine tumor models. The live tumor cells were significantly more immunogenic than irradiated or apoptotic tumor cells. We examined the interaction of live and apoptotic tumor cells with major subsets of antigen-presenting cells, i.e., CD8α

Tissue-resident macrophages are a diverse population of cells that perform specialized functions including sustaining tissue homeostasis and tissue surveillance. Here we report an interstitial subset of CD169(+) lung-resident macrophages that are transcriptionally and developmentally distinct from alveolar macrophages (AMs). They are primarily localized around the airways and are found in close proximity to the sympathetic nerves in the bronchovascular bundle. These nerve- and airway-associated macrophages (NAMs) are tissue-resident, yolk sac-derived, self-renewing, and do not require CCR2(+) monocytes for development or maintenance. Unlike AMs, the development of NAMs requires CSF1, but not GM-CSF. Bulk population and single cell transcriptome analysis indicated that NAMs are distinct from other lung resident macrophage subsets and highly express immunoregulatory genes under steady state and inflammatory conditions. NAMs proliferated robustly following influenza infection and activation with the TLR3 ligand poly(I:C), and in their absence, the inflammatory response was augmented resulting in excessive production of inflammatory cytokines and innate immune cell infiltration. Overall, our study provides insights into a distinct subset of airway-associated pulmonary macrophages that function to maintain immune and tissue homeostasis.

Aging has a profound impact on multiple facets of the immune system, culminating in aberrant functionality. The architectural disorganization of splenic white pulp is a hallmark of the aging spleen, yet the factors underlying these structural changes are unclear. Fibroblastic reticular cells comprise one stromal cell subset in the spleen that is important for maintenance of architectural organization, yet it remains to be determined how aging impacts these cells. In this study, we sought to determine how aging impacts splenic T cell zone reticular cell (TRC) numbers, morphology, and function. Using a mouse model of aging, we found that aged naive spleens have fewer TRCs than young spleens. This reduction in TRC number correlated with reduced CCL19 and CCL21 concentrations in aged spleens, which may contribute to impaired homing of T cells. CCL21 in both young and aged spleens localized with TRCs. Aged TRCs extended marginally into B cell follicles and may contribute to the blending of the T cell zone and B cell follicles in aged spleens. The described age-related changes in TRCs number and function may be an underlying factor contributing to impaired immune system function with age.

Background There is substantial evidence that signaling through Toll-like receptor 4 (TLR4) contributes to the pathogenesis of necrotizing enterocolitis (NEC). Pregnane X receptor (PXR), a xenobiotic sensor and signaling intermediate for certain host-bacterial metabolites, has been shown to negatively regulate TLR4 signaling. Here we investigated the relationship between PXR and TLR4 in the developing murine intestine and explored the capacity of PXR to modulate inflammatory pathways involved in experimental NEC. Methods Wild-type and PXR−/− mice were studied at various time points of development in an experimental model of NEC. In addition, we studied the ability of the secondary bile acid lithocholic acid (LCA), a known PXR agonist in liver, to activate intestinal PXR and reduce NEC-related intestinal inflammation. Results We found a reciprocal relationship between the developmental expression of PXR and TLR4 in wild-type murine intestine, with PXR acting to reduce TLR4 expression by decreasing TLR4 mRNA stability. In addition, PXR−/− mice exhibited a remarkably heightened severity of disease in experimental NEC. Moreover, LCA attenuated intestinal proinflammatory responses in the early stages of experimental NEC. Conclusion These findings provide proactive insights into the regulation of TLR4 in the developing intestine. Targeting PXR may be a novel approach for NEC prevention.

Alveolar macrophages (AMs) are considered the first line of defense in the airways. Exposure to harmful substances and certain infections can lead to dysfunction or depletion of AMs. Importantly, these conditions have been associated with increased risk of sepsis and acute lung injury. Staphylococcus aureus enterotoxins are superantigens that induce oligoclonal activation of T cells and a robust cytokine release, leading to systemic inflammatory response and tissue injury. In this study we investigated the relationship between S. aureus enterotoxins and AMs. Following inhalation, S. aureus enterotoxin was preferentially bound to AMs and MHC class II was not required. Furthermore, the enterotoxin was internalized and its presence in the cells decreased by 24 h after exposure. Ablation of AMs in CD169–diphtheria toxin receptor mice was associated with increased activation of enterotoxin-specific T cells and enhanced cytokine release into circulation. Thus, conditions causing depletion of AMs may increase the risk of S. aureus enterotoxin–induced diseases.

Despite mounting evidence for SARS-CoV-2 engagement with immune cells, most express little, if any, of the canonical receptor of SARS-CoV-2, ACE2. Here, using a myeloid-cell receptor-focused ectopic expression screen, we identified several C-type lectins (DC-SIGN, L-SIGN, LSECtin, ASGR1, and CLEC10A) and Tweety family member 2 (TTYH2) as glycan-dependent binding partners of the SARS-CoV-2 spike. Except for TTYH2, these molecules primarily interacted with spike via regions outside of the receptor-binding domain. Single-cell RNA-sequencing analysis of pulmonary cells from COVID-19 patients indicated predominant expression of these molecules on myeloid cells. Although these receptors do not support active replication of SARS-CoV-2, their engagement with virus induced robust proinflammatory responses in myeloid cells that correlated with COVID-19 severity. We also generated a bispecific anti-spike nanobody that not only blocked ACE2-mediated infection but also the myeloid receptors-mediated proinflammatory responses. Our findings suggest SARS-CoV-2-myeloid receptor interactions promote immune hyper-activation, which represents potential targets for COVID-19 therapy., Graphical Abstract, Most immune cells express little, if any, of the canonical SARS-CoV-2 receptor, ACE2. Lu et al. report that C-type lectins and TTYH2 act as SARS-CoV-2 myeloid cell-interacting partners that trigger immune hyper-activation, but not infection. These findings raise the possibility that these virus-myeloid cell interactions are directly involved in COVID-19 immunopathogenesis and could be targeted for COVID-19 therapy.

Background Multiple sclerosis (MS) is a central nervous system (CNS) autoimmune disease characterized by both inflammatory demyelination and impaired remyelination. Studies indicate that Toll-like receptor 2 (TLR2) signaling contributes to both the inflammatory component and the defective remyelination in MS. While most MS therapeutics target adaptive immunity, we recently reported that reducing TLR2 signaling in innate immune cells by inducing TLR2 tolerance attenuates adoptively transferred experimental autoimmune encephalomyelitis. Given that previous reports suggest TLR2 signaling also inhibits myelin repair, the objective of this study was to assess how reducing TLR2 signaling through TLR2 tolerance induction affects CNS myelin repair. Methods Chow containing 0.2% cuprizone was fed to male and female wild-type (WT) C57BL/6 mice or TLR2-deficient (TLR2−/−) mice for 5 weeks to induce demyelination. During a 2-week remyelination period following discontinuation of cuprizone, WT mice received either low dose TLR2 ligands to induce systemic TLR2 tolerance or vehicle control (VC). Remyelination was evaluated via electron microscopy and immunohistochemical analysis of microglia and oligodendrocytes in the corpus callosum. Statistical tests included 2-way ANOVA and Mann-Whitney U analyses. Results Inducing TLR2 tolerance in WT mice during remyelination significantly enhanced myelin recovery, restoring unmyelinated axon frequency and myelin thickness to baseline levels compared to VC-treated mice. Mechanistically, enhanced remyelination in TLR2 tolerized mice was associated with a shift in corpus callosum microglia from a pro-inflammatory iNOS+ phenotype to a non-inflammatory/pro-repair Arg1+ phenotype. This result was confirmed in vitro by inducing TLR2 tolerance in WT microglia cultures. TLR2−/− mice, without TLR2 tolerance induction, also significantly enhanced myelin recovery compared to WT mice, adding confirmation that reduced TLR2 signaling is associated with enhanced remyelination. Discussion Our results suggest that reducing TLR2 signaling in vivo by inducing TLR2 tolerance significantly enhances myelin repair. Furthermore, the enhanced remyelination resulting from TLR2 tolerance induction is associated with a shift in corpus callosum microglia from a pro-inflammatory iNOS+ phenotype to a non-inflammatory/pro-repair Arg1+ phenotype. While deletion of TLR2 would be an impractical approach in vivo, reducing innate immune signaling through TLR2 tolerance induction may represent a novel, two-pronged approach for treating both inflammatory and myelin repair components of MS. Electronic supplementary material The online version of this article (10.1186/s12974-019-1540-2) contains supplementary material, which is available to authorized users.

SummaryLymphoid cells that produce IL-17 cytokines protect barrier tissues from pathogenic microbes, but are also prominent effectors of inflammation and autoimmune disease. T-helper (TH17) cells, defined by RORγt-dependent production of IL-17A and IL-17F, exert homeostatic functions in the gut upon microbiota-directed differentiation from naïve CD4+ T cells. In the non-pathogenic setting, their cytokine production is regulated by serum amyloid A proteins (SAA1 and SAA2) secreted by adjacent intestinal epithelial cells. However, TH17 cell behaviors vary markedly according to their environment. Here we show that SAAs additionally direct a pathogenic pro-inflammatory TH17 cell differentiation program, acting directly on T cells in collaboration with STAT3-activating cytokines. Using loss- and gain-of-function mouse models, we show that SAA1, SAA2, and SAA3 have distinct systemic and local functions in promoting TH17-mediated inflammatory diseases. These studies suggest that T cell signaling pathways modulated by the SAAs may be attractive targets for anti-inflammatory therapies.

Lymphoid cells that produce IL-17 cytokines protect barrier tissues from pathogenic microbes, but are also prominent effectors of inflammation and autoimmune disease. T-helper (TH17) cells, defined by RORγt-dependent production of IL-17A and IL-17F, exert homeostatic functions in the gut upon microbiota-directed differentiation from naive CD4+ T cells. In the non-pathogenic setting, their cytokine production is regulated by serum amyloid A proteins (SAA1 and SAA2) secreted by adjacent intestinal epithelial cells. However, TH17 cell behaviors vary markedly according to their environment. Here we show that SAAs additionally direct a pathogenic pro-inflammatory TH17 cell differentiation program, acting directly on T cells in collaboration with STAT3-activating cytokines. Using loss- and gain-of-function mouse models, we show that SAA1, SAA2, and SAA3 have distinct systemic and local functions in promoting TH17-mediated inflammatory diseases. These studies suggest that T cell signaling pathways modulated by the SAAs may be attractive targets for anti-inflammatory therapies.

Memory γδ T cells are important for the clearance of Listeria monocytogenes infection in the intestinal mucosa. However, the mechanisms by which memory γδ T cells provide protection against secondary oral infection are poorly understood. Here we used a recombinant strain of L. monocytogenes that efficiently invades the intestinal epithelium to show that Vγ4+ memory γδ T cells represent a resident memory (Trm) population in the mesenteric lymph nodes (MLNs). The γδ Trm exhibited a remarkably static pattern of migration that radically changed following secondary oral L. monocytogenes infection. The γδ Trms produced IL-17A early after rechallenge and formed organized clusters with myeloid cells surrounding L. monocytogenes replication foci only after a secondary oral infection. Antibody blocking studies showed that in addition to IL-17A, the chemokine receptor C-X-C chemokine receptor 3 (CXCR3) is also important to enable the local redistribution of γδ Trm cells and myeloid cells specifically near the sites of L. monocytogenes replication within the MLN to restrict bacterial growth and spread. Our findings support a role for γδ Trms in orchestrating protective immune responses against intestinal pathogens.

Staphylococcus aureus enterotoxins cause debilitating systemic inflammatory responses, but how they spread systemically and trigger inflammatory cascade is unclear. In this study, we showed in mice that after inhalation, Staphylococcus aureus enterotoxin A rapidly entered the bloodstream and induced T cells to orchestrate systemic recruitment of inflammatory monocytes and neutrophils. To study the mechanism used by specific T cells that mediate this process, a systems approach revealed inducible and noninducible pathways as potential targets. It was found that TNF caused neutrophil entry into the peripheral blood, whereas CD28 signaling, but not TNF, was needed for chemotaxis of inflammatory monocytes into blood and lymphoid tissue. However, both pathways triggered local recruitment of neutrophils into lymph nodes. Thus, our findings revealed a dual mechanism of monocyte and neutrophil recruitment by T cells relying on overlapping and nonoverlapping roles for the noninducible costimulatory receptor CD28 and the inflammatory cytokine TNF. During sepsis, there might be clinical value in inhibiting CD28 signaling to decrease T cell–mediated inflammation and recruitment of innate cells while retaining bioactive TNF to foster neutrophil circulation.

Viral clearance requires effector T-cell egress from the draining lymph node (dLN). The mechanisms that regulate the complex process of effector T-cell egress from the dLN after infection are poorly understood. Here, we visualized endogenous pathogen-specific effector T-cell migration within, and from, the dLN. We used an inducible mouse model with a temporally disrupted sphingosine-1-phosphate receptor-1 (S1PR1) gene specifically in endogenous effector T cells. Early after infection, WT and S1PR1(-/-) effector T cells localized exclusively within the paracortex. This localization in the paracortex by CD8 T cells was followed by intranodal migration by both WT and S1PR1(-/-) T cells to positions adjacent to both cortical and medullary lymphatic sinuses where the T cells exhibited intense probing behavior. However, in contrast to WT, S1PR1(-/-) effector T cells failed to enter the sinuses. We demonstrate that, even when LN retention signals such as CC chemokine receptor 7 (CCR7) are down-regulated, T cell intrinsic S1PR1 is the master regulator of effector T-cell emigration from the dLN.

CCR7 is an important chemokine receptor that regulates T cell trafficking and compartmentalization within secondary lymphoid organs. However, the T cell–intrinsic role of CCR7 during infection in the spleen is not well understood. This study was designed to understand how CCR7-dependent localization and migration of CD8+ T cells in different compartments of the spleen affected the primary and recall responses after infection. To this end, we used adoptive transfer of naive Ag-specific CD8 T cells (OT-I) that either lacked CCR7 or constitutively expressed CCR7 (CD2-CCR7) in mice that were subsequently infected i.v. with Listeria monocytogenes. We show that naive CCR7−/−CD8+ T cells failed to enter the T cell zone, whereas CD2-CCR7 OT-I cells were exclusively confined to the T cell zones of the spleen. Surprisingly, however, CCR7−/− OT-I cells entered the T cell zones after infection, but the entry and egress migratory pattern of these cells was dysregulated and very distinct compared with wild-type OT-I cells. Moreover, CCR7-deficient OT-I cells failed to expand robustly when compared with wild-type OT-I cells and were preferentially skewed toward a short-lived effector cell differentiation pattern. Interestingly, CCR7−/−, CD2-CCR7, and wild-type OT-I memory cells responded equally well to rechallenge infection. These results highlight a novel role of CCR7 in regulating effector CD8 T cell migration in the spleen and demonstrate differential requirement of CCR7 for primary and secondary CD8 T cell responses to infection.

Tissue resident macrophages are a diverse population of cells that perform specialized functions: sustaining tissue homeostasis and tissue surveillance. Here we report an interstitial subset of CD169+ lung resident macrophages that are transcriptionally and developmentally distinct from alveolar macrophages (AM). They are primarily localized around the airways and in close contact with the innervating pulmonary nerves. These nerve and airway associated macrophages (NAMs) are tissue resident, yolk sac derived, self-renewing, and do not require CCR2+ monocytes for development or maintenance. We show that unlike AMs, CSF-1, but not CSF-2 is required for their development. Bulk population and single cell transcriptome analysis indicates that NAMs are distinct from other lung resident macrophage subsets and highly expressed immune regulatory genes under steady state and inflammatory conditions. NAMs proliferated robustly following TLR activation and influenza infection, and in their absence, the inflammatory response was remarkably augmented resulting in excessive production of inflammatory cytokines and innate immune cell infiltration. We show that AMs contribute to viral clearance while NAMs, contribute to regulating virus-induced inflammation in the lung. Overall, our study relates structure to function at a fundamental level, and provides essential insights into a distinct subset of resident macrophages in the lung that function to maintain immune and tissue homeostasis.

Sepsis affects more than 30 million people and accounts for approximately 6 million deaths worldwide each year. Current therapy consists of supportive care to keep organs functional and antibiotics to combat infections, with survival contingent on early detection. Our current knowledge of the cellular/molecular mechanisms that regulate the inflammatory pathways resulting in septic shock is limited. Notably, we know little about the precise populations of immune cells that play a central role during sepsis. To bridge these gaps in our knowledge, we examined the role of CD169+ macrophages in septic shock. We utilized both CD169-cre and CD169-diphtheria toxin receptor (DTR) mice to conditionally knockout (CKO) genes and selectively and temporally deplete CD169+ macrophage, respectively. We report that CD169+ macrophages, signaling pathways, and even the CD169 receptor is critical for protection against LPS shock. We show that in the absence of these macrophages, sensors, or the receptor; mice treated with sublethal LPS fail to survive and exhibit increased inflammatory cytokines and impaired IL-10 production. We also show that in the absence of these macrophages, mice exhibit increased dissemination of endotoxin to organs. Protection against LPS induced lethality is rescued by supplemental treatment with rIL-10. Lastly, we show that following LPS treatment, CD169+ macrophages are the initial targeted cell. These findings not only reveal a pivotal role for CD169+ macrophages and its sensing of LPS but also the role for the CD169 receptor as a critical mediator of protection from sepsis induced lethality, and provide new therapeutic targets against sepsis.

Listeria monocytogenes (Lm) is a common foodborne pathogen which causes mild gastrointestinal distress in healthy hosts, and systemic listeriosis in immunocompromised individuals. While immune responses have been rigorously examined after intravenous Lm infection, less is understood about Lm dissemination from the intestines or the induction of adaptive immune responses after physiologic infection through the consumption of contaminated food. Consequently, this study focused on the cells involved in early immune responses in the intestinal mucosa using foodborne Lm infection in mice. After foodborne infection, Lm trafficked intracellularly from the intestines to the mesenteric lymph nodes (MLN) and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this observation, dissemination of Lm from the gut to the MLN occurred normally in Batf3−/− mice. Activated migratory DC accumulated in the MLN by 3 days post-infection (dpi) where they surrounded Lm foci. At this time, Lm burden in the MLN was reduced in Batf3−/− mice implicating Batf3-DC in the maximal accumulation of Lm. While both conventional type 1 DC (cDC1) and type 2 DC in the MLN contained Lm by 3 dpi, Batf3−/− mice exhibited a profound defect in the induction and gut homing of Lm-specific CD8 T cells. Surprisingly, restoration of pathogen burden was unable to restore CD8 T cell responses in Batf3−/− mice. Thus, cDC1 play a critical role in the generation of potent anti-Lm immunity following foodborne infection. Collectively, these data demonstrate that DC play diverse and dynamic roles in the early events that follow foodborne Lm infection, and in the establishment of protective, anti-Lm intestinal immunity.