A mouse model for the human pathogen Salmonella typhi

Innate acting memory Th1 cells modulate heterologous diseases

Through immune memory, infections have a lasting effect on the host. While memory cells enable accelerated and enhanced responses upon rechallenge with the same pathogen, their impact on susceptibility to unrelated diseases is unclear. We identify a subset of memory T helper 1 (Th1) cells termed innate acting memory T (TIA) cells that originate from a viral infection and produce IFN-γ with innate kinetics upon heterologous challenge in vivo. Activation of memory TIA cells is induced in response to IL-12 in combination with IL-18 or IL-33 but is TCR independent. Rapid IFN-γ production by memory TIA cells is protective in subsequent heterologous challenge with the bacterial pathogen Legionella pneumophila. In contrast, antigen-independent reactivation of CD4+ memory TIA cells accelerates disease onset in an autoimmune model of multiple sclerosis. Our findings demonstrate that memory Th1 cells can acquire additional TCR-independent functionality to mount rapid, innate-like responses that modulate susceptibility to heterologous challenges.

Live-attenuated virus vaccine defective in RNAi suppression induces rapid protection in neonatal and adult mice lacking mature B and T cells

Global control of infectious diseases depends on the continuous development and deployment of diverse vaccination strategies. Currently available live-attenuated and killed virus vaccines typically take a week or longer to activate specific protection by the adaptive immunity. The mosquito-transmitted Nodamura virus (NoV) is attenuated in mice by mutations that prevent expression of the B2 viral suppressor of RNA interference (VSR) and consequently, drastically enhance in vivo production of the virus-targeting small-interfering RNAs. We reported recently that 2 d after immunization with live-attenuated VSR-disabled NoV (NoVΔB2), neonatal mice become fully protected against lethal NoV challenge and develop no detectable infection. Using Rag1-/- mice that produce no mature B and T lymphocytes as a model, here we examined the hypothesis that adaptive immunity is dispensable for the RNAi-based protective immunity activated by NoVΔB2 immunization. We show that immunization of both neonatal and adult Rag1-/- mice with live but not killed NoVΔB2 induces full protection against NoV challenge at 2 or 14 d postimmunization. Moreover, NoVΔB2-induced protective antiviral immunity is virus-specific and remains effective in adult Rag1-/- mice 42 and 90 d after a single-shot immunization. We conclude that immunization with the live-attenuated VSR-disabled RNA virus vaccine activates rapid and long-lasting protective immunity against lethal challenges by a distinct mechanism independent of the adaptive immunity mediated by B and T cells. Future studies are warranted to determine whether additional animal and human viruses attenuated by VSR inactivation induce similar protective immunity in healthy and adaptive immunity-compromised individuals.

Sexual dimorphism in skin immunity is mediated by an androgen-ILC2-dendritic cell axis

Males and females exhibit profound differences in immune responses and disease susceptibility. However, the factors responsible for sex differences in tissue immunity remain poorly understood. Here, we uncovered a dominant role for type 2 innate lymphoid cells (ILC2s) in shaping sexual immune dimorphism within the skin. Mechanistically, negative regulation of ILC2s by androgens leads to a reduction in dendritic cell accumulation and activation in males, along with reduced tissue immunity. Collectively, our results reveal a role for the androgen-ILC2-dendritic cell axis in controlling sexual immune dimorphism. Moreover, this work proposes that tissue immune set points are defined by the dual action of sex hormones and the microbiota, with sex hormones controlling the strength of local immunity and microbiota calibrating its tone.

Single missense mutations in Vi capsule synthesis genes confer hypervirulence to Salmonella Typhi

Many bacterial pathogens, including the human exclusive pathogen Salmonella Typhi, express capsular polysaccharides as a crucial virulence factor. Here, through S. Typhi whole genome sequence analyses and functional studies, we found a list of single point mutations that make S . Typhi hypervirulent. We discovered a single point mutation in the Vi biosynthesis enzymes that control the length or acetylation of Vi is enough to create different capsule variants of S. Typhi. All variant strains are pathogenic, but the hyper-capsule variants are particularly hypervirulent, as demonstrated by the high morbidity and mortality rates observed in infected mice. The hypo-capsule variants have primarily been identified in Africa, whereas the hyper-capsule variants are distributed worldwide. Collectively, these studies increase awareness about the existence of different capsule variants of S. Typhi, establish a solid foundation for numerous future studies on S. Typhi capsule variants, and offer valuable insights into strategies to combat capsulated bacteria.

A Monocytic Barrier to the Humanization of Immunodeficient Mice

Mice with severe immunodeficiencies have become very important tools for studying foreign cells in an in vivo environment. Xenotransplants can be used to model cells from many species, although most often, mice are humanized through the transplantation of human cells or tissues to meet the needs of medical research. The development of immunodeficient mice is reviewed leading up to the current state-of-the-art strains, such as the NOD-scid-gamma (NSG) mouse. NSG mice are excellent hosts for human hematopoietic stem cell transplants or immune reconstitution through transfusion of human peripheral blood mononuclear cells. However, barriers to full hematopoietic engraftment still remain; notably, the survival of human cells in the circulation is brief, which limits overall hematological and immune reconstitution. Reports have indicated a critical role for monocytic cells - monocytes, macrophages, and dendritic cells - in the clearance of xenogeneic cells from circulation. Various aspects of the NOD genetic background that affect monocytic cell growth, maturation, and function that are favorable to human cell transplantation are discussed. Important receptors, such as SIRPα, that form a part of the innate immune system and enable the recognition and phagocytosis of foreign cells by monocytic cells are reviewed. The development of humanized mouse models has taken decades of work in creating more immunodeficient mice, genetic modification of these mice to express human genes, and refinement of transplant techniques to optimize engraftment. Future advances may focus on the monocytic cells of the host to find ways for further engraftment and survival of xenogeneic cells.

The Salmonella Typhi SPI-2 injectisome enigma

The Salmonella pathogenicity island 2 (SPI-2)-encoded type III secretion system (injectisome) is assembled following uptake of bacteria into vacuoles in mammalian cells. The injectisome translocates virulence proteins (effectors) into infected cells. Numerous studies have established the requirement for a functional SPI-2 injectisome for growth of Salmonella Typhimurium in mouse macrophages, but the results of similar studies involving Salmonella Typhi and human-derived macrophages are not consistent. It is important to clarify the functions of the S. Typhi SPI-2 injectisome, not least because an inactivated SPI-2 injectisome forms the basis for live attenuated S. Typhi vaccines that have undergone extensive trials in humans. Intracellular expression of injectisome genes and effector delivery take longer in the S. Typhi/human macrophage model than for S. Typhimurium and we propose that this could explain the conflicting results. Furthermore, strains of both S. Typhimurium and S. Typhi contain intact genes for several 'core' effectors. In S. Typhimurium these cooperate to regulate the vacuole membrane and contribute to intracellular bacterial replication; similar functions are therefore likely in S. Typhi.

From Eberthella typhi to Salmonella Typhi: The Fascinating Journey of the Virulence and Pathogenicity of Salmonella Typhi

Salmonella Typhi (S. Typhi), the invasive typhoidal serovar of Salmonella enterica that causes typhoid fever in humans, is a severe threat to global health. It is one of the major causes of high morbidity and mortality in developing countries. According to recent WHO estimates, approximately 11-21 million typhoid fever illnesses occur annually worldwide, accounting for 0.12-0.16 million deaths. Salmonella infection can spread to healthy individuals by the consumption of contaminated food and water. Typhoid fever in humans sometimes is accompanied by several other critical extraintestinal complications related to the central nervous system, cardiovascular system, pulmonary system, and hepatobiliary system. Salmonella Pathogenicity Island-1 and Salmonella Pathogenicity Island-2 are the two genomic segments containing genes encoding virulent factors that regulate its invasion and systemic pathogenesis. This Review aims to shed light on a comparative analysis of the virulence and pathogenesis of the typhoidal and nontyphoidal serovars of S. enterica.

Murine Models of Salmonella Infection

The pathogen Salmonella enterica encompasses a range of bacterial serovars that cause intestinal inflammation and systemic infections in humans. Mice are a widely used infection model due to their relative simplicity and versatility. Here, we provide standardized protocols for culturing the prolific zoonotic pathogen S. enterica serovar Typhimurium for intragastric inoculation of mice to model colitis or systemic dissemination, along with techniques for direct extraintestinal infection. Furthermore, we present procedures for quantifying pathogen burden and for characterizing the immune response by analyzing tissue pathology, inflammatory markers, and immune cells from intestinal tissues. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Murine colitis model utilizing oral streptomycin pretreatment and oral S. Typhimurium administration Basic Protocol 2: Intraperitoneal injection of S. Typhimurium for modeling extraintestinal infection Support Protocol 1: Preparation of S. Typhimurium inoculum Support Protocol 2: Preparation of mixed S. Typhimurium inoculum for competitive infection Basic Protocol 3: Assessment of S. Typhimurium burden Support Protocol 3: Preservation and pathological assessment of S. Typhimurium-infected tissues Support Protocol 4: Measurement of inflammatory marker expression in intestinal tissues by qPCR Support Protocol 5: Preparation of intestinal content for inflammatory marker quantification by ELISA Support Protocol 6: Immune cell isolation from Salmonella-infected intestinal tissues.

Untangling Cellular Host-Pathogen Encounters at Infection Bottlenecks

Bacterial pathogens can invade the tissue and establish a protected intracellular niche at the site of invasion that can spread locally (e.g., microcolonies) or to systemic sites (e.g., granulomas). Invasion of the tissue and establishment of intracellular infection are rare events that are difficult to study in the in vivo setting but have critical clinical consequences, such as long-term carriage, reinfections, and emergence of antibiotic resistance. Here, I discuss Salmonella interactions with its host macrophage during early stages of infection and their critical role in determining infection outcome. The dynamics of host-pathogen interactions entail highly heterogenous host immunity, bacterial virulence, and metabolic cross talk, requiring in vivo analysis at single-cell resolution. I discuss models and single-cell approaches that provide a global understanding of the establishment of a protected intracellular niche within the tissue and the host-pathogen landscape at infection bottlenecks during early stages of infection. Studying cellular host-pathogen interactions in vivo can improve our knowledge of the trajectory of infection between the initial inoculation with a dose of pathogens and the appearance of symptoms of disease.

NFATc1 induction by an intronic enhancer restricts NKT γδ cell formation

In thymus, the ablation of T cell receptor (TCR)-activated transcription factor NFATc1 or its inducible isoforms during the double-negative (DN) stages of thymocyte development leads to a marked increase in γδ thymocytes whereas the development of αβ thymocytes remains mostly unaffected. These γδ thymocytes are characterized by the upregulation of the promyelocytic leukemia zinc-finger factor (PLZF), the "master regulator" of natural killer T (NKT) cell development, and the acquisition of an NKT γδ cell phenotype with higher cell survival rates. The suppressive function of NFATc1 in NKT γδ cell formation critically depends on the remote enhancer E2, which is essential for the inducible expression of NFATc1 directed by its distal promoter P1. Thus, the enhancer deciphers a strong γδ TCR signal into the expression of inducible NFATc1 isoforms resulting in high levels of NFATc1 protein that are essential to control the numbers of NKT γδ cells.

Targeted suppression of Dpt-specific B cells in humanized Rag2- γc- mouse model of HDM allergy

Der p 1 is one of the major allergenic molecules of Dermatophagoides pteronyssinus, causing house dust mite (HDM) allergy. The pathological B cells produce allergen-specific IgE antibodies that mediate the hypersensitivity reaction, therefore the selective elimination of these B cells is a legitimate therapeutic goal in allergy. Chimeric molecule Dp51-72 able to cross-link B cell inhibitory complement receptor type 1 and BCR on Der p 1-specific B cells was constructed. The signalling capabilities of this molecule have been tested on human B cells. A humanized mouse model of HDM allergy has been used to test the in vivo effects of the chimeric molecule administration. Administering the chimeric molecule to immunodeficient Rag2- γc- mice transferred with PBMCs from allergic patients resulted in reduction of allergen-specific IgE antibodies in the sera, and reduced infiltration of immune cells in lung histology preparations. Reduced numbers of human CD45⁺ and CD4⁺ cells in the lungs as well as inhibition of mast cell degranulation were also observed. The treatment with Dp51-72 chimera significantly decreased the local levels of anti-Dpt IgE antibodies in the bronchoalveolar lavage fluid (BALF). The binding of the chimeric molecule to tonsillar B cells triggers the tyrosine phosphorylation of 30-32 kDa protein, which is most likely involved in the inhibitory process. Administration of constructed chimeric molecules to humanized mice with developed inflammation resulted in specific suppression of disease-associated IgE antibody-producing cells and preserved lung histology. This effective approach could be further developed into a therapeutic agent for treatment of patients with HDM allergy.

Identification of collaborative cross mouse strains permissive to Salmonella enterica serovar Typhi infection

Salmonella enterica serovar Typhi is the causative agent of typhoid fever restricted to humans and does not replicate in commonly used inbred mice. Genetic variation in humans is far greater and more complex than that in a single inbred strain of mice. The Collaborative Cross (CC) is a large panel of recombinant inbred strains which has a wider range of genetic diversity than laboratory inbred mouse strains. We found that the CC003/Unc and CC053/Unc strains are permissive to intraperitoneal but not oral route of S. Typhi infection and show histopathological changes characteristic of human typhoid. These CC strains are immunocompetent, and immunization induces antigen-specific responses that can kill S. Typhi in vitro and control S. Typhi in vivo. Our results indicate that CC003/Unc and CC053/Unc strains can help identify the genetic basis for typhoid susceptibility, S. Typhi virulence mechanism(s) in vivo, and serve as a preclinical mammalian model system to identify effective vaccines and therapeutics strategies.

The evolutionary diversification of the Salmonella artAB toxin locus

Salmonella enterica is a diverse species of bacterial pathogens comprised of >2,500 serovars with variable host ranges and virulence properties. Accumulating evidence indicates that two AB₅-type toxins, typhoid toxin and ArtAB toxin, contribute to the more severe virulence properties of the Salmonella strains that encode them. It was recently discovered that there are two distinct types of artAB-like genetic elements in Salmonella: those that encode ArtAB toxins (artAB elements) and those in which the artA gene is degraded and the ArtB homolog, dubbed PltC, serves as an alternative delivery subunit for typhoid toxin (pltC elements). Here, we take a multifaceted approach to explore the evolutionary diversification of artAB-like genetic elements in Salmonella. We identify 7 subtypes of ArtAB toxins and 4 different PltC sequence groups that are distributed throughout the Salmonella genus. Both artAB and pltC are encoded within numerous diverse prophages, indicating a central role for phages in their evolutionary diversification. Genetic and structural analyses revealed features that distinguish pltC elements from artAB and identified evolutionary adaptations that enable PltC to efficiently engage typhoid toxin A subunits. For both pltC and artAB, we find that the sequences of the B subunits are especially variable, particularly amongst amino acid residues that fine tune the chemical environment of their glycan binding pockets. This study provides a framework to delineate the remarkably complex collection of Salmonella artAB/pltC-like genetic elements and provides a window into the mechanisms of evolution for AB₅-type toxins.

Divergent roles for the gut intraepithelial lymphocyte GLP-1R in control of metabolism, microbiota, and T cell-induced inflammation

Gut intraepithelial lymphocytes (IELs) are thought to calibrate glucagon-like peptide 1 (GLP-1) bioavailability, thereby regulating systemic glucose and lipid metabolism. Here, we show that the gut IEL GLP-1 receptor (GLP-1R) is not required for enteroendocrine L cell GLP-1 secretion and glucose homeostasis nor for the metabolic benefits of GLP-1R agonists (GLP-1RAs). Instead, the gut IEL GLP-1R is essential for the full effects of GLP-1RAs on gut microbiota. Moreover, independent of glucose control or weight loss, the anti-inflammatory actions of GLP-1RAs require the gut IEL GLP-1R to selectively restrain local and systemic T cell-induced, but not lipopolysaccharide-induced, inflammation. Such effects are mediated by the suppression of gut IEL effector functions linked to the dampening of proximal T cell receptor signaling in a protein-kinase-A-dependent manner. These data reposition key roles of the L cell-gut IEL GLP-1R axis, revealing mechanisms linking GLP-1R activation in gut IELs to modulation of microbiota composition and control of intestinal and systemic inflammation.

Monitoring autochthonous lung tumors induced by somatic CRISPR gene editing in mice using a secreted luciferase

Background

In vivo gene editing of somatic cells with CRISPR nucleases has facilitated the generation of autochthonous mouse tumors, which are initiated by genetic alterations relevant to the human disease and progress along a natural timeline as in patients. However, the long and variable, orthotopic tumor growth in inner organs requires sophisticated, time-consuming and resource-intensive imaging for longitudinal disease monitoring and impedes the use of autochthonous tumor models for preclinical studies.

Methods

To facilitate a more widespread use, we have generated a reporter mouse that expresses a Cre-inducible luciferase from Gaussia princeps (GLuc), which is secreted by cells in an energy-consuming process and can be measured quantitatively in the blood as a marker for the viable tumor load. In addition, we have developed a flexible, complementary toolkit to rapidly assemble recombinant adenoviruses (AVs) for delivering Cre recombinase together with CRISPR nucleases targeting cancer driver genes.

Results

We demonstrate that intratracheal infection of GLuc reporter mice with CRISPR-AVs efficiently induces lung tumors driven by mutations in the targeted cancer genes and simultaneously activates the GLuc transgene, resulting in GLuc secretion into the blood by the growing tumor. GLuc blood levels are easily and robustly quantified in small-volume blood samples with inexpensive equipment, enable tumor detection already several months before the humane study endpoint and precisely mirror the kinetics of tumor development specified by the inducing gene combination.

Conclusions

Our study establishes blood-based GLuc monitoring as an inexpensive, rapid, high-throughput and animal-friendly method to longitudinally monitor autochthonous tumor growth in preclinical studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01661-2.

Malnutrition and maternal vaccination against typhoid toxin

Children are particularly susceptible to typhoid fever caused by the bacterial pathogen Salmonella Typhi. Typhoid fever is prevalent in developing countries where diets can be less well-balanced. Here, using a murine model, we investigated the role of the macronutrient composition of the diet in maternal vaccination efficacies of two subunit vaccines targeting typhoid toxin: ToxoidVac and PltBVac. We found that maternal vaccinations protected all offspring against a lethal-dose typhoid toxin challenge in a balanced, normal diet (ND) condition, but the declined protection in a malnourished diet (MD) condition was observed in the PltBVac group. Despite the comparable antibody titers in both MD and ND mothers, MD offspring had a significantly lower level of typhoid toxin neutralizing antibodies than their ND counterparts. We observed a lower expression of the neonatal Fc receptor on the yolk sac of MD mothers than in ND mothers, agreeing with the observed lower antibody titers in MD offspring. Protein supplementation to MD diets, but not fat supplementation, increased FcRn expression and protected all MD offspring from the toxin challenge. Similarly, providing additional typhoid toxin-neutralizing antibodies to MD offspring was sufficient to protect all MD offspring from the toxin challenge. These results emphasize the significance of balanced/normal diets for a more effective maternal vaccination transfer to their offspring.

Typhoid fever is a life-threatening systemic infectious disease caused by Salmonella Typhi, which is prevalent in developing countries where diets can be less well-balanced. Here, we used mice to study the role of nutrition in maternal vaccination efficacies of two subunit vaccines targeting Salmonella’s typhoid toxin. We found maternal vaccinations protected all offspring from a lethal-dose typhoid toxin challenge in a balanced/normal diet (ND) condition, but the lack of protection in a malnourished diet (MD) condition was observed in the PltBVac group. Our data indicate that the difference in maternal vaccination outcomes between ND and MD offspring was due to the less effective maternal antibody transfer from MD mothers to their offspring. Providing additional proteins to MD mothers or additional toxin-neutralizing antibodies to MD offspring saved all malnourished offspring from a lethal-dose typhoid toxin challenge, highlighting the importance of balanced/normal diets for effective maternal vaccination outcomes.

The Game for Three: Salmonella–Host–Microbiota Interaction Models

Colonization of the gastrointestinal (GI) tract by enteric pathogens occurs in a context strongly determined by host-specific gut microbiota, which can significantly affect the outcome of infection. The complex gameplay between the trillions of microbes that inhabit the GI tract, the host, and the infecting pathogen defines a specific triangle of interaction; therefore, a complete model of infection should consider all of these elements. Many different infection models have been developed to explain the complexity of these interactions. This review sheds light on current knowledge, along with the strengths and limitations of in vitro and in vivo models utilized in the study of Salmonella–host–microbiome interactions. These models range from the simplest experiment simulating environmental conditions using dedicated growth media through in vitro interaction with cell lines and 3-D organoid structure, and sophisticated “gut on a chip” systems, ending in various animal models. Finally, the challenges facing this field of research and the important future directions are outlined.

Overexpression of wild type RRAS2, without oncogenic mutations, drives chronic lymphocytic leukemia

Background

Chronic lymphocytic leukemia (CLL) is the most frequent, and still incurable, form of leukemia in the Western World. It is widely accepted that cancer results from an evolutionary process shaped by the acquisition of driver mutations which confer selective growth advantage to cells that harbor them. Clear examples are missense mutations in classic RAS genes (KRAS, HRAS and NRAS) that underlie the development of approximately 13% of human cancers. Although autonomous B cell antigen receptor (BCR) signaling is involved and mutations in many tumor suppressor genes and oncogenes have been identified, an oncogenic driver gene has not still been identified for CLL.

Methods

Conditional knock-in mice were generated to overexpress wild type RRAS2 and prove its driver role. RT-qPCR analysis of a human CLL sample cohort was carried out to measure RRAS2 transcriptional expression. Sanger DNA sequencing was used to identify a SNP in the 3’UTR region of RRAS2 in human CLL samples. RNAseq of murine CLL was carried out to identify activated pathways, molecular mechanisms and to pinpoint somatic mutations accompanying RRAS2 overexpression. Flow cytometry was used for phenotypic characterization and shRNA techniques to knockdown RRAS2 expression in human CLL.

Results

RRAS2 mRNA is found overexpressed in its wild type form in 82% of the human CLL samples analyzed (n = 178, mean and median = 5-fold) as well as in the explored metadata. A single nucleotide polymorphism (rs8570) in the 3’UTR of the RRAS2 mRNA has been identified in CLL patients, linking higher expression of RRAS2 with more aggressive disease. Deliberate overexpression of wild type RRAS2 in mice, but not an oncogenic Q72L mutation in the coding sequence, provokes the development of CLL. Overexpression of wild type RRAS2 in mice is accompanied by a strong convergent selection of somatic mutations in genes that have been identified in human CLL. R-RAS2 protein is physically bound to the BCR and mediates BCR signals in CLL.

Conclusions

The results indicate that overexpression of wild type RRAS2 is behind the development of CLL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-022-01496-x.

Analysis of Salmonella Typhi Pathogenesis in a Humanized Mouse Model

Efforts to understand molecular mechanisms of pathogenesis of the human-restricted pathogen Salmonella enterica serovar Typhi, the causative agent of typhoid fever, have been hampered by the lack of a tractable small animal model. This obstacle has been surmounted by a humanized mouse model in which genetically modified mice are engrafted with purified CD34+ stem cells from human umbilical cord blood, designated CD34+ Hu-NSG (formerly hu-SRC-SCID) mice. We have shown that these mice develop a lethal systemic infection with S. Typhi that is dependent on the presence of engrafted human hematopoietic cells. Immunological and pathological features of human typhoid are recapitulated in this model, which has been successfully employed for the identification of bacterial genetic determinants of S. Typhi virulence. Here we describe the methods used to infect CD34+ Hu-NSG mice with S. Typhi in humanized mice and to construct and analyze a transposon-directed insertion site sequencing S. Typhi library, and provide general considerations for the use of humanized mice for the study of a human-restricted pathogen.

The IL-3, IL-5, and GM-CSF common receptor beta chain mediates oncogenic activity of FLT3-ITD-positive AML

FLT3-ITD is the most predominant mutation in AML being expressed in about one-third of AML patients and is associated with a poor prognosis. Efforts to better understand FLT3-ITD downstream signaling to possibly improve therapy response are needed. We have previously described FLT3-ITD-dependent phosphorylation of CSF2RB, the common receptor beta chain of IL-3, IL-5, and GM-CSF, and therefore examined its significance for FLT3-ITD-dependent oncogenic signaling and transformation. We discovered that FLT3-ITD directly binds to CSF2RB in AML cell lines and blasts isolated from AML patients. A knockdown of CSF2RB in FLT3-ITD positive AML cell lines as well as in a xenograft model decreased STAT5 phosphorylation, attenuated cell proliferation, and sensitized to FLT3 inhibition. Bone marrow from CSF2RB-deficient mice transfected with FLT3-ITD displayed decreased colony formation capacity and delayed disease onset together with increased survival upon transplantation into lethally irradiated mice. FLT3-ITD-dependent CSF2RB phosphorylation required phosphorylation of the FLT3 juxtamembrane domain at tyrosines 589 or 591, whereas the ITD insertion site and sequence were of no relevance. Our results demonstrate that CSF2RB participates in FLT3-ITD-dependent oncogenic signaling and transformation in vitro and in vivo. Thus, CSF2RB constitutes a rational treatment target in FLT3-ITD-positive AML.

Emerging technologies and infection models in cellular microbiology

The field of cellular microbiology, rooted in the co-evolution of microbes and their hosts, studies intracellular pathogens and their manipulation of host cell machinery. In this review, we highlight emerging technologies and infection models that recently promoted opportunities in cellular microbiology. We overview the explosion of microscopy techniques and how they reveal unprecedented detail at the host-pathogen interface. We discuss the incorporation of robotics and artificial intelligence to image-based screening modalities, biochemical mapping approaches, as well as dual RNA-sequencing techniques. Finally, we describe chips, organoids and animal models used to dissect biophysical and in vivo aspects of the infection process. As our knowledge of the infected cell improves, cellular microbiology holds great promise for development of anti-infective strategies with translational applications in human health.

CD4+ T cell immunity to Salmonella is transient in the circulation

While Salmonella enterica is seen as an archetypal facultative intracellular bacterial pathogen where protection is mediated by CD4⁺ T cells, identifying circulating protective cells has proved very difficult, inhibiting steps to identify key antigen specificities. Exploiting a mouse model of vaccination, we show that the spleens of C57BL/6 mice vaccinated with live-attenuated Salmonella serovar Typhimurium (S. Typhimurium) strains carried a pool of IFN-γ⁺ CD4⁺ T cells that could adoptively transfer protection, but only transiently. Circulating Salmonella-reactive CD4⁺ T cells expressed the liver-homing chemokine receptor CXCR6, accumulated over time in the liver and assumed phenotypic characteristics associated with tissue-associated T cells. Liver memory CD4⁺ T cells showed TCR selection bias and their accumulation in the liver could be inhibited by blocking CXCL16. These data showed that the circulation of CD4⁺ T cells mediating immunity to Salmonella is limited to a brief window after which Salmonella-specific CD4⁺ T cells migrate to peripheral tissues. Our observations highlight the importance of triggering tissue-specific immunity against systemic infections.

Helper T cells are essential for controlling infections by bacterial pathogens, such as Salmonella enterica var Typhimurium (S. Typhimurium). While it is well-established that this role is related to their provision of IFN-γ, when and where helper T cells elicit their protective function in vivo remains unresolved. We identified a protective helper T cell population in the circulation of mice early after inoculation with growth-attenuated S. Typhimurium strains; this population waned overtime. We observed that circulating helper T cell immunity can adoptively protect naïve recipient mice against lethal S. Typhimurium infection when harvested from a short time-window. In comparing helper T cell responses between spleen and liver in Salmonella-infected mice, we have observed a previously uncharacterized trafficking of helper T cells to the liver followed by the residence of S. Typhimurium-specific T cell memory in the organ. Taken together these findings identify that protective immunity to Salmonella infections is transient in the circulation and the liver as a preferential site of helper T memory cells.

Functional roles of graft-infiltrating lymphocytes during early-phase post-transplantation in mouse cardiac transplantation models

Immunological behavior of graft-infiltrating lymphocytes (GILs) determines the graft fate (i.e., rejection or acceptance). Nevertheless, the functional alloreactivity and the phenotype of GILs at various times during the early post-transplantation phase have not been fully elucidated. We examined the immunological activities of early-phase GILs using a murine model of cardiac transplantation. GILs from 120-h allografts, but not 72-h allografts, showed robust activation and produced proinflammatory cytokines. In particular, a significant increase in CD69⁺ T-bet⁺ Nur77⁺ T cells was detected in 120-h allografts. Furthermore, isolated GILs were used to reconstitute BALB/c Rag2^-/- γc^-/- (BRG) mice. BRG mice reconstituted with 120-h GILs displayed donor-specific immune reactivity and rejected donor strain cardiac allografts; conversely, 72-h GILs exhibited weak anti-donor reactivity and did not reject allografts. These findings were confirmed by re-transplantation of cardiac allografts into BRG mice at 72-h post-transplantation. Re-transplanted allografts continued to function for >100 days, despite the presence of CD3⁺ GILs. In conclusion, the immunological behavior of GILs considerably differs over time during the early post-transplantation phase. A better understanding of the functional role of early-phase GILs may clarify the fate determination process in the graft-site microenvironment.

Complete Genome Sequence of Salmonella enterica Serovar Typhi Strain ISP2825

Salmonella enterica serovar Typhi ISP2825, isolated in 1983 from a Chilean patient, is one of the major S. Typhi strains used for research, along with strains Ty2, CT18, and H58. The complete genome sequence of ISP2825, consisting of a 4,774,014-bp circular chromosome, will help us understand typhoid pathogenesis and evolution.

Global Genomic Characterization of Salmonella enterica Serovar Telelkebir

Non-typhoidal Salmonella (NTS) is a common cause for self-limiting gastroenteritis, representing a public health concern globally. NTS is one of the leading causes of foodborne illnesses in China; however, the invasive infection caused by NTS is largely underappreciated. Here, we reported an NTS invasive infection caused by an infrequently reported serovar Telelkebir (13,23:d:e,n,z15) strain FJ001 in China, which carries antimicrobial-resistant genes [fosA7 and aac(6')-Iaa] and typhoid-toxin genes (cdtB, pltA, and pltB). By conducting the whole genomic sequencing, we also investigated the relatedness of this strain with an additional 120 global contextual Salmonella enterica serovar Telelkebir (S. Telelkebir) isolates, and assessed the antimicrobial-resistant determinants and key virulence factors using the available genomic dataset. Notably, all 121 (100%) of the S. Telelkebir strains possessed the typhoid toxin genes cdtB, pltA, and pltB, and 58.67% (71/121) of S. Telelkebir harbored antimicrobial-resistant gene fosaA7. The study by core genome multilocus sequence typing (cgMLST) and core single-nucleotide polymorphism (SNP)-based phylogenomic analysis demonstrated that the S. Telelkebir isolates from different sources and locations clustered together. This suggests that regular international travels might increase the likelihood of rapid and extensive transmissions of potentially pathogenic bacteria. For the first time, our study revealed the antimicrobial resistance, virulence patterns, and genetic diversity of the serovar S. Telelkebir isolate in humans and similar isolates over the world. The present study also suggests that genomic investigation can facilitate surveillance and could offer added knowledge of a previously unknown threat with the unique combination of virulent and antimicrobial-resistant determinants.

New Insights on the Early Interaction Between Typhoid and Non-typhoid Salmonella Serovars and the Host Cells

Salmonella enterica is a common source of food and water-borne infections, causing a wide range of clinical ailments in both human and animal hosts. Immunity to Salmonella involves an interplay between different immune responses, which are rapidly initiated to control bacterial burden. However, Salmonella has developed several strategies to evade and modulate the host immune responses. In this sense, the main knowledge about the pathogenicity of this bacterium has been obtained by the study of mouse models with non-typhoidal serovars. However, this knowledge is not representative of all the pathologies caused by non-typhoidal serovars in the human. Here we review the most important features of typhoidal and non-typhoidal serovars and the diseases they cause in the human host, describing the virulence mechanisms used by these pathogens that have been identified in different models of infection.

Humanized Mice for Infectious and Neurodegenerative disorders

Humanized mice model human disease and as such are used commonly for research studies of infectious, degenerative and cancer disorders. Recent models also reflect hematopoiesis, natural immunity, neurobiology, and molecular pathways that influence disease pathobiology. A spectrum of immunodeficient mouse strains permit long-lived human progenitor cell engraftments. The presence of both innate and adaptive immunity enables high levels of human hematolymphoid reconstitution with cell susceptibility to a broad range of microbial infections. These mice also facilitate investigations of human pathobiology, natural disease processes and therapeutic efficacy in a broad spectrum of human disorders. However, a bridge between humans and mice requires a complete understanding of pathogen dose, co-morbidities, disease progression, environment, and genetics which can be mirrored in these mice. These must be considered for understanding of microbial susceptibility, prevention, and disease progression. With known common limitations for access to human tissues, evaluation of metabolic and physiological changes and limitations in large animal numbers, studies in mice prove important in planning human clinical trials. To these ends, this review serves to outline how humanized mice can be used in viral and pharmacologic research emphasizing both current and future studies of viral and neurodegenerative diseases. In all, humanized mouse provides cost-effective, high throughput studies of infection or degeneration in natural pathogen host cells, and the ability to test transmission and eradication of disease.

Mechanisms of typhoid toxin neutralization by antibodies targeting glycan receptor binding and nuclease subunits

Nearly all clinical isolates of Salmonella Typhi, the cause of typhoid fever, are antibiotic resistant. All S. Typhi isolates secrete an A2B5 exotoxin called typhoid toxin to benefit the pathogen during infection. Here, we demonstrate that antibiotic-resistant S. Typhi secretes typhoid toxin continuously during infection regardless of antibiotic treatment. We characterize typhoid toxin antibodies targeting glycan-receptor-binding PltB or nuclease CdtB, which neutralize typhoid toxin in vitro and in vivo, as demonstrated by using typhoid toxin secreted by antibiotic-resistant S. Typhi during human cell infection and lethal dose typhoid toxin challenge to mice. TyTx11 generated in this study neutralizes typhoid toxin effectively, comparable to TyTx4 that binds to all PltB subunits available per holotoxin. Cryoelectron microscopy explains that the binding of TyTx11 to CdtB makes this subunit inactive through CdtB catalytic-site conformational change. The identified toxin-neutralizing epitopes are conserved across all S. Typhi clinical isolates, offering critical insights into typhoid toxin-neutralizing strategies.

Long-Term Anti-Bacterial Immunity against Systemic Infection by Salmonella enterica Serovar Typhimurium Elicited by a GMMA-Based Vaccine

Salmonella Typhimurium (STm) represents the most prevalent cause of invasive non-typhoidal Salmonella (iNTS) disease, and currently no licensed vaccine is available. In this work we characterized the long-term anti-bacterial immunity elicited by a STm vaccine based on Generalized Modules of Membrane Antigens (GMMA) delivering O:4,5 antigen, using a murine model of systemic infection. Subcutaneous immunization of mice with STmGMMA/Alhydrogel elicited rapid, high, and persistent antigen-specific serum IgG and IgM responses. The serum was bactericidal in vitro. O:4,5-specific IgG were also detected in fecal samples after immunization and positively correlated with IgG observed in intestinal washes. Long-lived plasma cells and O:4,5-specific memory B cells were detected in spleen and bone marrow. After systemic STm challenge, a significant reduction of bacterial load in blood, spleen, and liver, as well as a reduction of circulating neutrophils and G-CSF glycoprotein was observed in STmGMMA/Alhydrogel immunized mice compared to untreated animals. Taken together, these data support the development of a GMMA-based vaccine for prevention of iNTS disease.

Activating an adaptive immune response from a hydrogel scaffold imparts regenerative wound healing

Microporous annealed particle (MAP) scaffolds are flowable, in situ crosslinked, microporous scaffolds composed of microgel building blocks and were previously shown to accelerate wound healing. To promote more extensive tissue ingrowth before scaffold degradation, we aimed to slow MAP degradation by switching the chirality of the crosslinking peptides from L- to D-amino acids. Unexpectedly, despite showing the predicted slower enzymatic degradation in vitro, D-peptide crosslinked MAP hydrogel (D-MAP) hastened material degradation in vivo and imparted significant tissue regeneration to healed cutaneous wounds, including increased tensile strength and hair neogenesis. MAP scaffolds recruit IL-33 type 2 myeloid cells, which is amplified in the presence of D-peptides. Remarkably, D-MAP elicited significant antigen-specific immunity against the D-chiral peptides, and an intact adaptive immune system was required for the hydrogel-induced skin regeneration. These findings demonstrate that the generation of an adaptive immune response from a biomaterial is sufficient to induce cutaneous regenerative healing despite faster scaffold degradation.

TCF7 is not essential for glucose homeostasis in mice

Objective

Glucose-dependent insulinotropic polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1) are incretin hormones that exert overlapping yet distinct actions on islet β-cells. We recently observed that GIP, but not GLP-1, upregulated islet expression of Transcription Factor 7 (TCF7), a gene expressed in immune cells and associated with the risk of developing type 1 diabetes. TCF7 has also been associated with glucose homeostasis control in the liver. Herein we studied the relative metabolic importance of TCF7 expression in hepatocytes vs. islet β-cells in mice.

Methods

Tcf7 expression was selectively inactivated in adult mouse hepatocytes using adenoviral Cre expression and targeted in β-cells using two different lines of insulin promoter-Cre mice. Glucose homeostasis, plasma insulin and triglyceride responses, islet histology, hepatic and islet gene expression, and body weight gain were evaluated in mice fed regular chow or high fat diets. Tcf7 expression within pancreatic islets and immune cells was evaluated using published single cell RNA-seq (scRNA-seq) data, and in islet RNA from immunodeficient Rag2^−/−Il2rg^−/− mice.

Results

Reduction of hepatocyte Tcf7 expression did not impair glucose homeostasis, lipid tolerance or hepatic gene expression profiles linked to control of metabolic or immune pathways. Similarly, oral and intraperitoneal glucose tolerance, plasma insulin responses, islet histology, body weight gain, and insulin tolerance were not different in mice with targeted recombination of Tcf7 in insulin-positive β-cells. Surprisingly, islet Tcf7 mRNA transcripts were not reduced in total islet RNA containing endocrine and associated non-endocrine cell types from Tcf7^{βcell−/−} mice, despite Cre-mediated recombination of islet genomic DNA. Furthermore, glucose tolerance was normal in whole body Tcf7^−/− mice. Analysis of scRNA-seq datasets localized pancreatic Tcf7 expression to islet progenitors during development, and immune cells, but not within differentiated islet β-cells or endocrine lineages within mature islets. Moreover, the expression of Tcf7 was extremely low in islet RNA from Rag2^−/−Il2rg^−/− mice and, consistent with expression within immune cells, Tcf7 was highly correlated with levels of Cd3g mRNA transcripts in RNA from wild type mouse islets.

Conclusions

These findings demonstrate that Tcf7 expression is not a critical determinant of glucose homeostasis in mice. Moreover, the detection of Tcf7 expression within islet mRNA is attributable to the expression of Tcf7 RNA in islet-associated murine immune cells, and not in islet β-cells.

•Reduction of hepatocyte Tcf7 does not impair glucose homeostasis.

•Targeting beta cell Tcf7 using insulin-promoter-Cre does not reduce islet Tcf7 expression.

•RNA-seq localizes pancreatic Tcf7 to islet progenitors and lymphocytes.

•Tcf7 expression is markedly reduced in islet RNA from Rag2^−/−Il2rg^−/− mice.

The NK cell granule protein NKG7 regulates cytotoxic granule exocytosis and inflammation

Immune-modulating therapies have revolutionized the treatment of chronic diseases, particularly cancer. However, their success is restricted and there is a need to identify new therapeutic targets. Here, we show that natural killer cell granule protein 7 (NKG7) is a regulator of lymphocyte granule exocytosis and downstream inflammation in a broad range of diseases. NKG7 expressed by CD4+ and CD8+ T cells played key roles in promoting inflammation during visceral leishmaniasis and malaria-two important parasitic diseases. Additionally, NKG7 expressed by natural killer cells was critical for controlling cancer initiation, growth and metastasis. NKG7 function in natural killer and CD8+ T cells was linked with their ability to regulate the translocation of CD107a to the cell surface and kill cellular targets, while NKG7 also had a major impact on CD4+ T cell activation following infection. Thus, we report a novel therapeutic target expressed on a range of immune cells with functions in different immune responses.

Influenza Infection Induces Alveolar Macrophage Dysfunction and Thereby Enables Noninvasive Streptococcus pneumoniae to Cause Deadly Pneumonia

Secondary Streptococcus pneumoniae infection is a significant cause of morbidity and mortality during influenza epidemics and pandemics. Multiple pathogenic mechanisms, such as lung epithelial damage and dysregulation of neutrophils and alveolar macrophages (AMs), have been suggested to contribute to the severity of disease. However, the fundamental reasons for influenza-induced susceptibility to secondary bacterial pneumonia remain unclear. In this study, we revisited these controversies over key pathogenic mechanisms in a lethal model of secondary bacterial pneumonia with an S. pneumoniae strain that is innocuous to mice in the absence of influenza infection. Using a series of in vivo models, we demonstrate that rather than a systemic suppression of immune responses or neutrophil function, influenza infection activates IFN-γR signaling and abrogates AM-dependent bacteria clearance and thereby causes extreme susceptibility to pneumococcal infection. Importantly, using mice carrying conditional knockout of Ifngr1 gene in different myeloid cell subsets, we demonstrate that influenza-induced IFN-γR signaling in AMs impairs their antibacterial function, thereby enabling otherwise noninvasive S. pneumoniae to cause deadly pneumonia.

Salmonella Persistence and Host Immunity Are Dictated by the Anatomical Microenvironment

The intracellular bacterial pathogen Salmonella is able to evade the immune system and persist within the host. In some cases, these persistent infections are asymptomatic for long periods and represent a significant public health hazard because the hosts are potential chronic carriers, yet the mechanisms that control persistence are incompletely understood. Using a mouse model of chronic typhoid fever combined with major histocompatibility complex (MHC) class II tetramers to interrogate endogenous, Salmonella-specific CD4⁺ helper T cells, we show that certain host microenvironments may favorably contribute to a pathogen's ability to persist in vivo We demonstrate that the environment in the hepatobiliary system may contribute to the persistence of Salmonella enterica subsp. enterica serovar Typhimurium through liver-resident immunoregulatory CD4⁺ helper T cells, alternatively activated macrophages, and impaired bactericidal activity. This contrasts with lymphoid organs, such as the spleen and mesenteric lymph nodes, where these same cells appear to have a greater capacity for bacterial killing, which may contribute to control of bacteria in these organs. We also found that, following an extended period of infection of more than 2 years, the liver appeared to be the only site that harbored Salmonella bacteria. This work establishes a potential role for nonlymphoid organ immunity in regulating chronic bacterial infections and provides further evidence for the hepatobiliary system as the site of chronic Salmonella infection.

Salmonella Typhoid Toxin PltB Subunit and Its Non-typhoidal Salmonella Ortholog Confer Differential Host Adaptation and Virulence

Typhoidal and non-typhoidal Salmonelleae (NTS) cause typhoid fever and gastroenteritis, respectively, in humans. Salmonella typhoid toxin contributes to typhoid disease progression and chronic infection, but little is known about the role of its NTS ortholog. We found that typhoid toxin and its NTS ortholog induce different clinical presentations. The PltB subunit of each toxin exhibits different glycan-binding preferences that correlate with glycan expression profiles of host cells targeted by each bacterium at the primary infection or intoxication sites. Through co-crystal structures of PltB subunits bound to specific glycan receptor moieties, we show that they induce markedly different glycan-binding preferences and virulence outcomes. Furthermore, immunization with the NTS S. Javiana or its toxin offers cross-reactive protection against lethal-dose typhoid toxin challenge. Cumulatively, these results offer insights into the evolution of host adaptations in Salmonella AB toxins, their cell and tissue tropisms, and the design for improved typhoid vaccines and therapeutics.

Improved mouse models and advanced genetic and genomic technologies for the study of neutrophils

Mice have been excellent surrogates for studying neutrophil biology and, furthermore, murine models of human disease have provided fundamental insights into the roles of human neutrophils in innate immunity. The emergence of novel humanized mice and high-diversity mouse populations offers the research community innovative and powerful platforms for better understanding, respectively, the mechanisms by which human neutrophils drive pathogenicity, and how genetic differences underpin the variation in neutrophil biology observed among humans. Here, we review key examples of these new resources. Additionally, we provide an overview of advanced genetic engineering tools available to further improve such murine model systems, of sophisticated neutrophil-profiling technologies, and of multifunctional nanoparticle (NP)-based neutrophil-targeting strategies.

Endogenous PAD4 in Breast Cancer Cells Mediates Cancer Extracellular Chromatin Network Formation and Promotes Lung Metastasis

Peptidyl arginine deiminase 4 (PAD4/PADI4) is a posttranslational modification enzyme that converts protein arginine or mono-methylarginine to citrulline. The PAD4-mediated hypercitrullination reaction in neutrophils causes the release of nuclear chromatin to form a chromatin network termed neutrophil extracellular traps (NET). NETs were first described as antimicrobial fibers that bind and kill bacteria. However, it is not known whether PAD4 can mediate the release of chromatin DNA into the extracellular space of cancer cells. Here, we report that murine breast cancer 4T1 cells expressing high levels of PADI4 can release cancer extracellular chromatin networks (CECN) in vitro and in vivo. Deletion of Padi4 using CRISPR/Cas9 abolished CECN formation in 4T1 cells. Padi4 deletion from 4T1 cells also reduced the rate of tumor growth in an allograft model, and decreased lung metastasis by 4T1 breast cancers. DNase I treatment, which degrades extracellular DNA including CECNs, also reduced breast to lung metastasis of Padi4 wild-type 4T1 cells in allograft experiments in the Padi4-knockout mice. We further demonstrated that DNase I treatment in this mouse model did not alter circulating tumor cells but decreased metastasis through steps after intravasation. Taken together, our genetic studies show that PAD4 plays a cell autonomous role in cancer metastasis, thus revealing a novel strategy for preventing cancer metastasis by inhibiting cancer cell endogenous PAD4. IMPLICATIONS: This study shows that PADI4 can mediate the formation of CECNs in 4T1 cells, and that endogenous PADI4 plays an essential role in breast cancer lung metastasis. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/18/5/735/F1.large.jpg.

An Advanced Human Intestinal Coculture Model Reveals Compartmentalized Host and Pathogen Strategies during Salmonella Infection

Infection research routinely employs in vitro cell cultures or in vivo mouse models as surrogates of human hosts. Differences between murine and human immunity and the low level of complexity of traditional cell cultures, however, highlight the demand for alternative models that combine the in vivo-like properties of the human system with straightforward experimental perturbation. Here, we introduce a 3D tissue model comprising multiple cell types of the human intestinal barrier, a primary site of pathogen attack. During infection with the foodborne pathogen Salmonella enterica serovar Typhimurium, our model recapitulates human disease aspects, including pathogen restriction to the epithelial compartment, thereby deviating from the systemic infection in mice. Combination of our model with state-of-the-art genetics revealed Salmonella-mediated local manipulations of human immune responses, likely contributing to the establishment of the pathogen’s infection niche. We propose the adoption of similar 3D tissue models to infection biology, to advance our understanding of molecular infection strategies employed by bacterial pathogens in their human host.

A major obstacle in infection biology is the limited ability to recapitulate human disease trajectories in traditional cell culture and animal models, which impedes the translation of basic research into clinics. Here, we introduce a three-dimensional (3D) intestinal tissue model to study human enteric infections at a level of detail that is not achieved by conventional two-dimensional monocultures. Our model comprises epithelial and endothelial layers, a primary intestinal collagen scaffold, and immune cells. Upon Salmonella infection, the model mimics human gastroenteritis, in that it restricts the pathogen to the epithelial compartment, an advantage over existing mouse models. Application of dual transcriptome sequencing to the Salmonella-infected model revealed the communication of epithelial, endothelial, monocytic, and natural killer cells among each other and with the pathogen. Our results suggest that Salmonella uses its type III secretion systems to manipulate STAT3-dependent inflammatory responses locally in the epithelium without accompanying alterations in the endothelial compartment. Our approach promises to reveal further human-specific infection strategies employed by Salmonella and other pathogens.

Insulin-like Growth Factor 1 Supports a Pulmonary Niche that Promotes Type 3 Innate Lymphoid Cell Development in Newborn Lungs

Type 3 innate lymphoid cells (ILC3s) are critical for lung defense against bacterial pneumonia in the neonatal period, but the signals that guide pulmonary ILC3 development remain unclear. Here, we demonstrated that pulmonary ILC3s descended from ILC precursors that populated a niche defined by fibroblasts in the developing lung. Alveolar fibroblasts produced insulin-like growth factor 1 (IGF1), which instructed expansion and maturation of pulmonary ILC precursors. Conditional ablation of IGF1 in alveolar fibroblasts or deletion of the IGF-1 receptor from ILC precursors interrupted ILC3 biogenesis and rendered newborn mice susceptible to pneumonia. Premature infants with bronchopulmonary dysplasia, characterized by interrupted postnatal alveolar development and increased morbidity to respiratory infections, had reduced IGF1 concentrations and pulmonary ILC3 numbers. These findings indicate that the newborn period is a critical window in pulmonary immunity development, and disrupted lung development in prematurely born infants may have enduring effects on host resistance to respiratory infections.

Susceptibility of aging mice to listeriosis: Role of anti-inflammatory responses with enhanced Treg-cell expression of CD39/CD73 and Th-17 cells

Foodborne Listeria monocytogenes (Lm) causes serious illness and death in immunosuppressed hosts, including the elderly population. We investigated Lm susceptibility and inflammatory cytokines in geriatric mice. Young-adult and old mice were gavaged with a Lm strain Lmo-InlA^m. Tissues were assayed for Lm burden and splenocytes were analyzed for Th1/Th2/Th17/Treg responses and expression of CD39 and CD73. Old Lm-infected mice lost body-weight dose-dependently, had higher Lm colonization, and showed higher inflammatory responses than Lm-infected young-adult mice. After infection, IL-17 levels increased significantly in old mice whereas IFN-γ levels were unchanged. Levels of IL-10 and Treg cells were increased in infected old mice as compared to infected young-adult mice. Age-dependent enhanced expression of CD39/CD73 was observed in purified Treg prior to infection, suggesting increased baseline adenosine production in old mice. Lm lysate-treated splenocytes from older mice produced significantly higher levels of IL-10, IL17, and IL-1β, produced less IFN-γ and IL-2, and proliferated less than splenocytes from young-adult mice. Data suggests that older mice maybe more susceptible to Lm infection due to an imbalance of Th cell responses with disproportionate and persistent anti-inflammatory responses. Lm infection enhanced differentiation of proinflammatory Th17 cells, which may also exacerbate pathological responses during listeriosis.

Type 1 Innate Lymphoid Cells Protect Mice from Acute Liver Injury via Interferon-γ Secretion for Upregulating Bcl-xL Expression in Hepatocytes

Although type 1 innate lymphoid cells (ILC1s) have been originally found as liver-resident ILCs, their pathophysiological role in the liver remains poorly investigated. Here, we demonstrated that carbon tetrachloride (CCl₄) injection into mice activated ILC1s, but not natural killer (NK) cells, in the liver. Activated ILC1s produced interferon-γ (IFN-γ) and protected mice from CCl₄-induced acute liver injury. IFN-γ released from activated ILC1s promoted the survival of hepatocytes through upregulation of Bcl-xL. An activating NK receptor, DNAM-1, was required for the optimal activation and IFN-γ production of liver ILC1s. Extracellular adenosine triphosphate accelerated interleukin-12-driven IFN-γ production by liver ILC1s. These findings suggest that ILC1s are critical for tissue protection during acute liver injury.

Prophylactic potential of cytolethal distending toxin B (CdtB) subunit of typhoid toxin against Typhoid fever

Typhoid fever caused by Salmonella enterica serovar Typhi (S.Typhi) continues to be a major problem, especially in developing countries. Due to the rapid emergence of multi-drug-resistant (MDR) strains, which limits the efficacy of conventional antibiotics as well as problems associated with the existing vaccines, efforts are being made to develop effective prophylactic agents. CdtB subunit of typhoid toxin was selected for assessing its vaccine potential due to its high conservation throughout the Typhi strains. In-vitro assessment of DNase activity of cloned and purified CdtB protein showed a significant decrease in the band intensity of DNA. The measure of metabolic activity and morphological alterations assessed using different cell lines in the presence of CdtB protein showed no significant signs of toxicity. These observations were further strengthened by cell cycle analysis, assessed by flow cytometry. Keeping these observations in mind, the immunoprotective potential of CdtB was assessed using S.Typhi induced mouse peritonitis model. A significant titer of IgG antibodies (>128000) against CdtB protein was recorded in the immunized mice by enzyme-linked immunosorbent assay (ELISA), which was also validated by immunoblotting. Active immunization with the protein protected 75% mice against a lethal dose of S.Typhi Ty2. The data indicated a significant (up to 5 log) reduction in the bacterial load in the spleen and liver of immunized-infected mice compared to control (unimmunized-infected) mice which might have resulted in the modulation of histoarchitecture of spleen and liver and the levels of cytokines (IL-6, TNF-α and IL-10) production; thereby indicating the effectiveness of the subunit. The observations deduced from the study give the proof of concept of immunogenic potential of protein. However, further studies involving the immunoreactivity of CdtB with the statistically significant number of sera samples obtained from the human patients would be helpful in establishing the relevance of CdtB protein in humans and for making the strategies to develop it as an effective vaccine candidate.

CD271+ Human Mesenchymal Stem Cells Show Antiarrhythmic Effects in a Novel Murine Infarction Model

Background: Ventricular arrhythmias (VA) are a common cause of sudden death after myocardial infarction (MI). Therefore, developing new therapeutic methods for the prevention and treatment of VA is of prime importance. Methods: Human bone marrow derived CD271⁺ mesenchymal stem cells (MSC) were tested for their antiarrhythmic effect. This was done through the development of a novel mouse model using an immunocompromised Rag2^−/− γc^−/− mouse strain subjected to myocardial “infarction-reinfarction”. The mice underwent a first ischemia-reperfusion through the left anterior descending (LAD) artery closure for 45 min with a subsequent second permanent LAD ligation after seven days from the first infarct. Results: This mouse model induced various types of VA detected with continuous electrocardiogram (ECG) monitoring via implanted telemetry device. The immediate intramyocardial delivery of CD271⁺ MSC after the first MI significantly reduced VA induced after the second MI. Conclusions: In addition to the clinical relevance, more closely reflecting patients who suffer from severe ischemic heart disease and related arrhythmias, our new mouse model bearing reinfarction warrants the time required for stem cell engraftment and for the first time enables us to analyze and verify significant antiarrhythmic effects of human CD271⁺ stem cells in vivo.

Human macrophages and innate lymphoid cells: Tissue-resident innate immunity in humanized mice

Macrophages and innate lymphoid cells (ILCs) are tissue-resident cells that play important roles in organ homeostasis and tissue immunity. Their intricate relationship with the organs they reside in allows them to quickly respond to perturbations of organ homeostasis and environmental challenges, such as infection and tissue injury. Macrophages and ILCs have been extensively studied in mice, yet important species-specific differences exist regarding innate immunity between humans and mice. Complementary to ex-vivo studies with human cells, humanized mice (i.e. mice with a human immune system) offer the opportunity to study human macrophages and ILCs in vivo within their surrounding tissue microenvironments. In this review, we will discuss how humanized mice have helped gain new knowledge about the basic biology of these cells, as well as their function in infectious and malignant conditions. Furthermore, we will highlight active areas of investigation related to human macrophages and ILCs, such as their cellular heterogeneity, ontogeny, tissue residency, and plasticity. In the near future, we expect more fundamental discoveries in these areas through the combined use of improved humanized mouse models together with state-of-the-art technologies, such as single-cell RNA-sequencing and CRISPR/Cas9 genome editing.

Spontaneous atopic dermatitis in mice with a defective skin barrier is independent of ILC2 and mediated by IL-1β

BACKGROUND

Atopic dermatitis (AD) is one of the most common skin diseases with a multifactorial etiology. Mutations leading to loss of skin barrier function are associated with the development of AD with group 2 innate lymphoid cells (ILC2) promoting acute skin inflammation. Filaggrin-mutant (Flgft/ft ) mice develop spontaneous skin inflammation accompanied by an increase in skin ILC2 numbers, IL-1β production, and other cytokines recapitulating human AD. Here, we investigated the role of ILC2, effector cytokines, inflammasome activation, and mast cell function on the development of chronic AD-like inflammation in mice.

METHODS

Mice with a frameshift mutation in the filaggrin gene develop spontaneous dermatitis. Flgft/ft mice were crossed to cell- or cytokine-deficient mouse strains, or bred under germ-free conditions. Skin inflammation was scored, and microbiome composition was analyzed. Skin protein expression was measured by multiplex immunoassay. Infiltrating cells were analyzed by flow cytometry.

RESULTS

Wild-type and Flgft/ft mice significantly differ in their microbiome composition. Furthermore, mutant mice do not develop skin inflammation under germ-free conditions. ILC2 deficiency did not ameliorate chronic dermatitis in Flgft/ft mice, which was also independent of IL-4, IL-5, IL-9, IL-13, IL-17A, and IL-22. Inflammation was independent of NLRP3 inflammasome activation but required IL-1β and IL-1R1-signaling. Mechanistically, IL-1β promoted hyperactivation of IL-1R1-expressing mast cells. Treatment with anti-IL-1β-antibody alleviated dermatitis exacerbation, while antibiotic intervention ameliorated dermatitis in neonatal mice but not in adults with established inflammation.

CONCLUSIONS

In summary, we identified a critical role for the microbiome and IL-1β mediating chronic inflammation in mice with an impaired skin barrier.

Typhoid Fever: The More We Learn, the Less We Know (Apologies, Albert Einstein)

In this issue of Cell Host & Microbe, Karlinsey et al. (2019) combine TraDIS with humanized mice to identify genes required for early replication of Salmonella Typhi in vivo. Surprisingly, some expected virulence traits and genes appear dispensable in the replication of S. Typhi, supporting findings from a recent human challenge study by Gibani et al. (2019).

Genome-wide Analysis of Salmonella enterica serovar Typhi in Humanized Mice Reveals Key Virulence Features

Salmonella enterica serovar Typhi causes typhoid fever only in humans. Murine infection with S. Typhimurium is used as a typhoid model, but its relevance to human typhoid is limited. Non-obese diabetic-scid IL2rγnull mice engrafted with human hematopoietic stem cells (hu-SRC-SCID) are susceptible to lethal S. Typhi infection. In this study, we use a high-density S. Typhi transposon library in hu-SRC-SCID mice to identify virulence loci using transposon-directed insertion site sequencing (TraDIS). Vi capsule, lipopolysaccharide (LPS), and aromatic amino acid biosynthesis were essential for virulence, along with the siderophore salmochelin. However, in contrast to the murine S. Typhimurium model, neither the PhoPQ two-component system nor the SPI-2 pathogenicity island was required for lethal S. Typhi infection, nor was the CdtB typhoid toxin. These observations highlight major differences in the pathogenesis of typhoid and non-typhoidal Salmonella infections and demonstrate the utility of humanized mice for understanding the pathogenesis of a human-specific pathogen.

Investigation of the role of typhoid toxin in acute typhoid fever in a human challenge model

Salmonella Typhi is a human host-restricted pathogen that is responsible for typhoid fever in approximately 10.9 million people annually¹. The typhoid toxin is postulated to have a central role in disease pathogenesis, the establishment of chronic infection and human host restriction^2–6. However, its precise role in typhoid disease in humans is not fully defined. We studied the role of typhoid toxin in acute infection using a randomized, double-blind S. Typhi human challenge model⁷. Forty healthy volunteers were randomized (1:1) to oral challenge with 10⁴ colony-forming units of wild-type or an isogenic typhoid toxin deletion mutant (TN) of S. Typhi. We observed no significant difference in the rate of typhoid infection (fever ≥38 °C for ≥12 h and/or S. Typhi bacteremia) between participants challenged with wild-type or TN S. Typhi (15 out of 21 (71%) versus 15 out of 19 (79%); P = 0.58). The duration of bacteremia was significantly longer in participants challenged with the TN strain compared with wild-type (47.6 hours (28.9–97.0) versus 30.3(3.6–49.4); P ≤ 0.001). The clinical syndrome was otherwise indistinguishable between wild-type and TN groups. These data suggest that the typhoid toxin is not required for infection and the development of early typhoid fever symptoms within the context of a human challenge model. Further clinical data are required to assess the role of typhoid toxin in severe disease or the establishment of bacterial carriage.

Typhoid toxin is not essential for the pathogenesis of typhoid fever in healthy humans challenged with Salmonella Typhi.

T Lymphocyte Development and Activation in Humanized Mouse Model

Humanized mice, containing engrafted human cells and tissues, are emerging as an important in vivo platform for studying human diseases. Since the development of Nod scid gamma (NSG) mice bearing mutations in the IL-2 receptor gamma chain, many investigators have used NSG mice engrafted with human hematopoietic stem cells (HSCs) to generate functional human immune systems in vivo, results in high efficacy of human cell engraftment. The development of NSG mice has allowed significant advances to be made in studies on several human diseases, including cancer and graft-versus-host-disease (GVHD), and in regenerative medicine. Based on the human HSC transplantation, organ transplantation including thymus and liver in the renal capsule has been performed. Also, immune reconstruction of cells, of the lymphoid as well as myeloid lineages, has been partly accomplished. However, crosstalk between pluripotent stem cell derived therapeutic cells with human leukocyte antigen (HLA) mis/matched types and immune CD3 T cells have not been fully addressed. To overcome this hurdle, human major histocompatibility complex (MHC) molecules, not mouse MHC molecules, are required to generate functional T cells in a humanized mouse model. Here, we briefly summarize characteristics of the humanized mouse model, focusing on development of CD3 T cells with MHC molecules. We also highlight the necessity of the humanized mouse model for the treatment of various human diseases.

Induction of acute graft vs. host disease in lymphopenic mice

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially life-saving treatment for refractory/relapsing hematological malignancies, blood disorders or autoimmune diseases. However, approximately 40-50% of patients undergoing allogeneic HSCT will develop a multi-organ, inflammatory disorder called acute graft vs. host disease (aGVHD). Experimental and clinical studies suggest that intestinal injury due to toxic, pre-transplant conditioning protocols (e.g. lethal irradiation and/or chemotherapy) may play a major role in the development of aGVHD. However, recent studies from our laboratory suggest that this may not be the case. The objective of this study was to quantify and compare the onset and severity of aGVHD induced by the adoptive transfer of allogeneic T cells into untreated lymphopenic mice. Four million allogeneic or syngeneic CD4⁺CD62L⁺CD25^- T cells were transferred (i.p.) into NK cell-depleted RAG1^-/- mice or RAG2^-/-IL2rγ^-/-double knock-out (DKO) mice and assessed daily for signs of aGVHD. We found that adoptive transfer of allogeneic but not syngeneic T cells into NK cell-depleted RAG1^-/- or DKO mice induced many of the clinical and histological features of aGVHD including weight loss, inflammatory cytokine production and tissue inflammation. In addition, adoptive transfer of allogeneic T cells into each recipient induced severe anemia as well as dramatic reductions in bone marrow and spleen cellularity. Taken together, we conclude that allogeneic CD4⁺ T cells are both necessary and sufficient to induce aGVHD in lymphopenic recipients in the absence of toxic, pre-transplant conditioning.