Infant Mice Research Articles

Effects of sDR5-Fc fusion protein on infant mice with ulcerative colitis via the TRAIL-DR5 pathway.

To explore effects of the sDR5-Fc fusion protein on ulcerative colitis of infant mice via the TRAIL-DR5 pathway, 50 female mice were randomly divided into 5 groups, i.e., control group (group A), dextran sulfate sodium group (group B), hIgG group (group C), 10 mg/kg sDR5-Fc group (group D), and 20 mg/ kg sDR5-Fc group (group E). The acute ulcerative colitis models were established. The weights and disease activity index (DAI) of each group were monitored daily. In addition, the pathological changes of colon tissues were observed by Hematoxylin-Eosin staining. The number of macrophages in colon tissues was detected by immunohistochemistry assay. Changes in the expression of inflammatory factors in colon tissues were detected by quantitative real-time polymerase chain reaction (PCR). Lipopolysaccharide (LPS) of different concentrations was utilized alone or in combination with TRAIL to stimulate the NCM460 cells. The activation of NLRP3 inflammasomes was detected by Western blot. The apoptosis of NCM460 cells was detected by flow cytometry. The results showed that in groups B and C, the body weights decreased, the DAI increased, the colon epithelial cells were injured, the inflammatory cells were infiltrated, and the macrophages in colon tissues increased significantly. In groups D and E, the body weights increased, the DAI decreased, the inflammation was significantly improved, the macrophages decreased significantly, and the gene expression levels of NLRP3, Caspase-1, and IL-1β decreased significantly. Thus, sDR5-Fc could inhibit the activation of NLRP3 inflammasomes induced by TRAIL, thereby decreasing the apoptosis of NCM460 cells. In conclusion, the sDR5-Fc fusion protein could block the TRAIL-DR5 pathway to reduce the expression of NLRP3 inflammasomes, thereby improving ulcerative colitis.

Comparisons of infant and adult mice reveal age effects for liver depot gene therapy in Pompe disease

Comparisons of infant and adult mice reveal age effects for liver depot gene therapy in Pompe disease

Early life experiences selectively mature learning and memory abilities

The mechanisms underlying the maturation of learning and memory abilities are poorly understood. Here we show that episodic learning produces unique biological changes in the hippocampus of infant rats and mice compared to juveniles and adults. These changes include persistent neuronal activation, BDNF-dependent increase in the excitatory synapse markers synaptophysin and PSD-95, and significant maturation of AMPA receptor synaptic responses. Inhibition of PSD-95 induction following learning impairs both AMPA receptor response maturation and infantile memory, indicating that the synapse formation/maturation is necessary for creating infantile memories. Conversely, capturing the learning-induced changes by presenting a subsequent learning experience or by chemogenetic activation of the neural ensembles tagged by learning matures memory functional competence. This memory competence is selective for the type of experience encountered, as it transfers within similar hippocampus-dependent learning domains but not to other hippocampus-dependent types of learning. Thus, experiences in early life produce selective maturation of memory abilities.

Environmental Tobacco Smoke During the Early Postnatal Period of Mice Interferes With Brain 18 F-FDG Uptake From Infancy to Early Adulthood - A Longitudinal Study.

Exposure to environmental tobacco smoke (ETS) is associated with high morbidity and mortality, mainly in childhood. Our aim was to evaluate the effects of postnatal ETS exposure in the brain 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) uptake of mice by positron emission tomography (PET) neuroimaging in a longitudinal study. C57BL/6J mice were exposed to ETS that was generated from 3R4F cigarettes from postnatal day 3 (P3) to P14. PET analyses were performed in male and female mice during infancy (P15), adolescence (P35), and adulthood (P65). We observed that ETS exposure decreased 18F-FDG uptake in the whole brain, both left and right hemispheres, and frontal cortex in both male and female infant mice, while female infant mice exposed to ETS showed decreased 18F-FDG uptake in the cerebellum. In addition, all mice showed reduced 18F-FDG uptake in infancy, compared to adulthood in all analyzed VOIs. In adulthood, ETS exposure during the early postnatal period decreased brain 18F-FDG uptake in adult male mice in the cortex, striatum, hippocampus, cingulate cortex, and thalamus when compared to control group. ETS induced an increase in 18F-FDG uptake in adult female mice when compared to control group in the brainstem and cingulate cortex. Moreover, male ETS-exposed animals showed decreased 18F-FDG uptake when compared to female ETS-exposed in the whole brain, brainstem, cortex, left amygdala, striatum, hippocampus, cingulate cortex, basal forebrain and septum, thalamus, hypothalamus, and midbrain. The present study shows that several brain regions are vulnerable to ETS exposure during the early postnatal period and these effects on 18F-FDG uptake are observed even a long time after the last exposure. This study corroborates our previous findings, strengthening the idea that exposure to tobacco smoke in a critical period interferes with brain development of mice from late infancy to early adulthood.

Supplemental Material for Ethanol Exposure During the Brain Growth Spurt Impairs Habituation and Promotes Locomotor Hyperactivity of Infant Mice in the Tail Suspension Test

Supplemental Material for Ethanol Exposure During the Brain Growth Spurt Impairs Habituation and Promotes Locomotor Hyperactivity of Infant Mice in the Tail Suspension Test

Nucleoside-modified mRNA vaccination partially overcomes maternal antibody inhibition of de novo immune responses in mice.

Maternal antibodies provide short-term protection to infants against many infections. However, they can inhibit de novo antibody responses in infants elicited by infections or vaccination, leading to increased long-term susceptibility to infectious diseases. Thus, there is a need to develop vaccines that are able to elicit protective immune responses in the presence of antigen-specific maternal antibodies. Here, we used a mouse model to demonstrate that influenza virus-specific maternal antibodies inhibited de novo antibody responses in mouse pups elicited by influenza virus infection or administration of conventional influenza vaccines. We found that a recently developed influenza vaccine, nucleoside-modified mRNA encapsulated in lipid nanoparticles (mRNA-LNP), partially overcame this inhibition by maternal antibodies. The mRNA-LNP influenza vaccine established long-lived germinal centers in the mouse pups and elicited stronger antibody responses than did a conventional influenza vaccine approved for use in humans. Vaccination with mRNA-LNP vaccines may offer a promising strategy for generating robust immune responses in infants in the presence of maternal antibodies.

Interaction between autophagy, apoptosis and necrosis of infant mice (Mus musculus) brain cells from its carbofuran exposed mothers during lactation periods

This study aimed to determine the mechanism of autophagy, apoptosis and necrosis in the neurons of infant mice (Mus musculus) whose mothers were exposed to carbofuran during the lactation period. This experimental study included 20 mice; carbofuran was administered at LD50 fractions by gavage to mice at the doses of 1.25 mg/kg body weight (BW) (1/4 LD50), 0.625 mg/kg BW (1/8 LD50), and 0.3125 mg/kg BW (1/16 LD50). Mothers were exposed to carbofuran during lactation on Days 1–9. On Day 10, infant mice were sacrificed in order to determine the number of neuron cells expressing protein kinase B (Akt) and the mammalian target of rapamycin complex 1 (mTORC1) as autophagy pathway using immunohistochemistry, apoptosis using the Tunel Assay, and necrosis using haematoxylin and eosin staining. The results of Akt, mTORC1, apoptosis, and cell necrosis were analyzed by analysis of variance (ANOVA) and Duncan tests. The results of the study showed that exposing the mothers to carbofuran during lactation caused an increase in necrosis and apoptosis of neuronal cells but did not cause autophagy in neuron cells via the Akt/mTOR pathway of infant mice. The increase in apoptotic neurons opens up opportunities for the prevention and handling of the effects of reactive oxygen species activities due to carbofuran exposure during lactation periods.

Comparisons of Infant and Adult Mice Reveal Age Effects for Liver Depot Gene Therapy in Pompe Disease

Pompe disease is caused by the deficiency of lysosomal acid α-glucosidase (GAA). It is expected that gene therapy to replace GAA with adeno-associated virus (AAV) vectors will be less effective early in life because of the rapid loss of vector genomes. AAV2/8-LSPhGAA (3 × 1010 vector genomes [vg]/mouse) was administered to infant (2-week-old) or adult (2-month-old) GAA knockout mice. AAV vector transduction in adult mice significantly corrected GAA deficiency in the heart (p < 0.0001), diaphragm (p < 0.01), and quadriceps (p < 0.001) for >50 weeks. However, in infant mice, the same treatment only partially corrected GAA deficiency in the heart (p < 0.05), diaphragm (p < 0.05), and quadriceps (p < 0.05). The clearance of glycogen was much more efficient in adult mice compared with infant mice. Improved wire hang test latency was observed for treated adults (p < 0.05), but not for infant mice. Abnormal ventilation was corrected in both infant and adult mice. Vector-treated female mice demonstrated functional improvement, despite a lower degree of biochemical correction compared with male mice. The relative vector dose for infants was approximately 3-fold higher than adults, when normalized to body weight at the time of vector administration. Given these data, the dose requirement to achieve similar efficacy will be higher for the treatment of young patients.

Developmental and cellular age direct conversion of CD4+ T cells into RORγ+ or Helios+ colon Treg cells.

RORγ+ and Helios+ Treg cells in the colon are phenotypically and functionally distinct, but their origins and relationships are poorly understood. In monocolonized and normal mice, single-cell RNA-seq revealed sharing of TCR clonotypes between these Treg cell populations, potentially denoting a common progenitor. In a polyclonal Treg cell replacement system, naive conventional CD4+ (Tconv) cells, but not pre-existing tTregs, could differentiate into RORγ+ pTregs upon interaction with gut microbiota. A smaller proportion of Tconv cells converted into Helios+ pTreg cells, but these dominated when the Tconv cells originated from preweaning mice. T cells from infant mice were predominantly immature, insensitive to RORγ-inducing bacterial cues and to IL6, and showed evidence of higher TCR-transmitted signals, which are also characteristics of recent thymic emigrants (RTEs). Correspondingly, transfer of adult RTEs or Nur77high Tconv cells mainly yielded Helios+ pTreg cells, recapitulating the infant/adult difference. Thus, CD4+ Tconv cells can differentiate into both RORγ+ and Helios+ pTreg cells, providing a physiological adaptation of colonic Treg cells as a function of the age of the cell or of the individual.

Poison frog moms and dads use similar brain cells for parenting

![Graphic][1] Parenting is hard, and everyone takes a different approach. Infant mice are usually reared by mom, whereas songbirds tend to be exemplar co-parents. While scientists know how parenting gets kick-started in feathered and furry vertebrates, other animals, such as poison frogs (

Effects of curcumin on pulmonary inflammation and p38 expression in an infant murine model of pneumococcal pneumonia

Objective To investigate the effects of curcumin on pneumococcal pneumonia-induced pneumonia, apoptosis and p38 MAPK expression in infant mice. Methods A total of 60 male infant C57BL/6 mice at three weeks of age were randomly divided into 6 groups: control group, model group, high-dose curcumin treatment group, middle-dose curcumin treatment group, low-dose curcumin treatment group and SB203580 treatment group. The Curcumin and SB203580 were intraperitoneally applied at doses of 200, 60, and 20 mg/kg (for curcumin) and 100 mg/kg (for SB203580) from two days before bacterial infection to three days post-infection. The control group and model group were intraperitoneally injected with an equal volume of saline. The model group, curcumin treatment groups and SB203580 treatment group were transnasally inoculated with approximately 106 CFU/ml of pneumococcal pneumonia in 50 μl of PBS applied to the tip of the nose to establish the experimental pneumococcal pneumonia. Subsequently, all the mice were killed and lung tissues were harvested for hematoxylin-eosin staining, calculation of lung score indexes, measurement of IL-1β and TNF-α contents by ELISA, and measurement of Bax, Bcl-2and p38 MAPK expression by Western blot. Results Compared to the model group, the edema score (0.50 ± 0.10, 1.51 ± 0.16, 1.38±0.11, vs. 2.50 ± 0.20), hemorrhage score (0.32 ± 0.09, 1.01 ± 0.11, 0.85±0.09 vs. 1.80 ± 0.20), inflammatory cell infiltrate score (0.35 ± 0.09, 1.61 ± 0.16, 1.52±0.10 vs. 3.21 ± 0.22), small airway damage score (0.12 ± 0.03, 0.53 ± 0.14, 0.50±0.04 vs. 1.12 ± 0.19) in the medium-, high-dose group and SB203580 treatment group significantly decreased (P<0.01). Compared to the model group, the contents of IL-1β (20.38 ± 1.69 pg/ml, 25.73 ± 2.08 pg/ml vs. 40.22 ± 5.70 pg/ml) and TNF-α (160.39 ± 15.81 pg/ml, 198.67 ± 18.97 pg/ml vs. 282.22 ± 25.30 pg/ml), Bax/Bcl-2 (0.31 ± 0.05, 0.53 ± 0.06 vs. 1.79 ± 0.17) and expression of phosphorylated p38 MAPK (0.69 ± 0.05, 0.81 ± 0.07 vs. 1.71 ± 0.14) in the high-dose group and SB203580 treeatment group significantly decreased (P<0.01). Conclusions Curcumin can inhibit the inflammatory response and cellular apoptosis in the lungs of mice with pneumococcal pneumonia, and the mechanisms maybe related to its inhibition of p38 MAPK expression. Key words: Curcumin; Pneumonia; Pneumococcal infections; Apoptosis; Inflammation; p38 Mitogen-activated protein kinases; Mice

Neonatal priming and infancy boosting with a novel respiratory syncytial virus vaccine induces protective immune responses without concomitant respiratory disease upon RSV challenge

ABSTRACT Although respiratory syncytial virus (RSV) infection in infants and young children is a global public health issue, development of a safe RSV vaccine has been impeded by formalin-inactivated RSV-enhanced respiratory disease (ERD). In developing a safer yet effective RSV vaccine for children, a strategy to decrease over-reactive T cells and increase neutralizing anti-RSV antibodies should be considered. We previously demonstrated that adult mice immunized with RSV recombinant G protein plus low-dose Cyclosporine A (G+ CsA) could, upon subsequent RSV challenge, produce increased levels of antigen-specific T regulatory cells in lungs that overcame the ERD. Neutralizing anti-RSV antibodies that prevented viral infection were also elicited. In this study, we investigated if such a G+ CsA vaccine could provide infant mice with the same protection from RSV infection without ERD. The results showed that the G+ CsA vaccine could prevent RSV infection with only a mild loss of body weight. Importantly, there was nearly normal morphology and no mucus appearance in lung tissues after RSV challenge. These results demonstrate that the G+ CsA vaccine strategy achieved similar benefits in the neonatal prime and infancy boost model as in the adult mouse model. The G+ CsA immunization strategy is potentially safe and effective in neonates and infants because it suppresses the devastating ERD.

Maternal Antibodies Elicited by Immunization With an O- Polysaccharide Glycoconjugate Vaccine Protect Infant Mice Against Lethal Salmonella Typhimurium Infection.

Non-typhoidal Salmonella (NTS) are a leading cause of pediatric invasive bacterial infections in sub-Saharan Africa with high associated case fatality rates in children under 5 years old. We have developed glycoconjugate vaccines consisting of the lipid A-removed surface polysaccharide of NTS, core and O-polysaccharide (COPS), and the flagellar monomer protein (FliC) from the homologous serovar as the carrier. We previously established that COPS:FliC was immunogenic and protective in mice immunized as adults or infants; however, the brief period of murine infancy precluded the evaluation of protection against invasive NTS (iNTS) disease in early life. In the present study, we used a mouse model of maternal immunization to investigate transmission of S. Typhimurium COPS:FliC-induced maternal antibodies and protection against lethal iNTS challenge in infant mice. We found that vaccinated dams developed high levels of COPS- and FliC-specific IgG, which were transferred to their offspring. Sera from both vaccinated mothers and their litters mediated complement-dependent bactericidal activity in-vitro. Passively immunized 2-week old infant mice born to vaccinated mothers were fully protected from challenge with an S. Typhimurium blood isolate from sub-Saharan Africa. The pre-clinical findings reported herein demonstrate that anti-COPS:FliC antibodies induced by vaccination are sufficient for protection of murine infants against experimental S. Typhimurium infection. By underscoring the protective role of antibody, our results suggest that maintaining an adequate titer of protective anti-Salmonella antibodies during early life, either through pediatric or maternal COPS:FliC vaccination, may reduce iNTS disease in young children in sub-Saharan Africa.

A Novel Peptide Nucleic Acid against the Cytidine Monophosphate Kinase of S. aureus Inhibits Staphylococcal Infection In Vivo

Here, we report a novel bactericidal peptide nucleic acid (PNA) that can induce the antisense effect on the cytidine monophosphate kinase (Cmk) of Staphylococcus aureus, a putative essential component for bacterial species. Based on the genome sequence of S. aureus N315, a set of PNA conjugates with a bacterial penetration peptide, (KFF)3K, were synthesized to target the seven potentially essential genes (cmk, deoD, ligA, smpB, glmU, pyrH, and ftsA) and further evaluated for their antibacterial properties in vitro as well as in vivo. The results demonstrated that two peptide-conjugated PNAs (P-PNAs), antisense P-PNA (ASP)-cmk1 and ASP-deoD1, targeting either the cmk or the deoD genes, had the strongest inhibitory effects on the growth of S. aureus ATCC 29740 (a bovine mastitic milk isolate) in a dose-dependent manner. In vivo application of ASP-cmk1 resulted in a significant reduction of bacterial loads in mice intraperitoneally infected with a sublethal dose of S. aureus. Moreover, ASP-cmk1 significantly increased the survival rate of the breast-fed infant mice after intramammary infection of the lactating CD-1 mice. Taken together, our characterization of ASP-cmk1 demonstrated its bactericidal activity against S. aureus as well as its effectiveness in vivo.

Remarkable characterization and determination of atypical E. coli O157 none producing shiga toxin which can produce cytopathic effect on Vero cell and diarrhea in mice

This study focused on the cytopathic effect of an unusual form of E. coli O157:H7 (atypical E. coli O157 (a-O157)) on Vero cell and infant mice. Multiplex PCR assay showed that they did not carry the gene for either shiga toxin 1 (stx1) or stx2 and other virulence factors. Increased changes in epithelial cell morphology, inter and intracellular gap junction and invading were assessed using Vero assay. In addition, a-O157infection causes disruptions of intercellular tight junctions, leading to clinical sequelae that include acute diarrhea in mice. Vero cell monolayers were exposed to a-O157influx and disintegrated tight junction of Vero cell line. Infected Vero cell enhance the number of attaching and effacing (A/E) lesions. Collectively, these findings provide in vitro evidence that Vero cell infected by a-O157was shown injury in epithelial cell barrier and induced A/E lesion the same as E. coli O157:H7 stx positive. These variants cannot be diagnosed by routine monitoring methods like biochemical assay for E. coli O157:H7 stx positive control. Finally, the data suggest that not only typical but also a-O157are an important cause of diarrhea in mice and produce cytopathic effect on Vero cell and may be harmful for food animal and also human.

Characterization of the Vibrio cholerae Phage Shock Protein Response.

The phage shock protein (Psp) system is a stress response pathway that senses and responds to inner membrane damage. The genetic components of the Psp system are present in several clinically relevant Gram-negative bacteria, including Vibrio cholerae However, most of the current knowledge about the Psp response stems from in vitro studies in Escherichia coli and Yersinia enterocolitica In fact, the Psp response in V. cholerae has remained completely uncharacterized. In this study, we demonstrate that V. cholerae does have a functional Psp response system. We found that overexpression of GspD (EpsD), the type II secretion system secretin, induces the Psp response, whereas other V. cholerae secretins do not. In addition, we have identified several environmental conditions that induce this stress response. Our studies on the genetic regulation and induction of the Psp system in V. cholerae suggest that the key regulatory elements are conserved with those of other Gram-negative bacteria. While a psp null strain is fully capable of colonizing the infant mouse intestine, it exhibits a colonization defect in a zebrafish model, indicating that this response may be important for disease transmission in the environment. Overall, these studies provide an initial understanding of a stress response pathway that has not been previously investigated in V. choleraeIMPORTANCEVibrio cholerae leads a dual life cycle, as it can exist in the aquatic environment and colonize the human small intestine. In both life cycles, V. cholerae encounters a variety of stressful conditions, including fluctuating pH and temperature and exposure to other agents that may negatively affect cell envelope homeostasis. The phage shock protein (Psp) response is required to sense and respond to such insults in other bacteria but has remained unstudied in V. cholerae Interestingly, the Psp system has protein homologs, principally, PspA, in a number of bacterial clades as well as in archaea and plants. Therefore, our findings not only fill a gap in knowledge about an unstudied extracytoplasmic stress response in V. cholerae, but also may have far-reaching implications.

BeATing back obesity

Immunology![Figure][1] Lipids in breast milk delay the transition from beige to white adipose tissue and protect against obesity. PHOTO: LIFEBRARY/SHUTTERSTOCK.COM Children who are breastfed appear to be at a lower risk for obesity later in life. One explanation is that breast milk may somehow prevent the premature transition from beige adipose tissue (BeAT) to white adipose tissue during childhood and adolescence. Yu et al. report that alkylglycerol ether lipids found in breast milk maintain the BeAT of infant mice. Adipose tissue macrophages metabolize these lipids into platelet-activating factor, which then induces macrophage release of interleukin-6, signal transducer and activator of transcription 3 (STAT3) signaling in adipocytes, and the development of BeAT. Although usually inactivated in adulthood, this pathway resurrects in obese adipose tissue, indicating a degree of metabolic flexibility that could be exploited for therapeutic applications. J. Clin. Invest. 129 , 2485 (2019). [1]: pending:yes

A unique combination adjuvant modulates immune responses preventing vaccine-enhanced pulmonary histopathology after a single dose vaccination with fusion protein and challenge with respiratory syncytial virus

Alum adjuvanted formalin-inactivated respiratory syncytial virus (RSV) vaccination resulted in enhanced respiratory disease in young children upon natural infection. Here, we investigated the adjuvant effects of monophosphoryl lipid A (MPL) and oligodeoxynucleotide CpG (CpG) on vaccine-enhanced respiratory disease after fusion (F) protein prime vaccination and RSV challenge in infant and adult mouse models. Combination CpG + MPL adjuvant in RSV F protein single dose priming of infant and adult age mice was found to promote the induction of IgG2a isotype antibodies and neutralizing activity, and lung viral clearance after challenge. CpG + MPL adjuvanted F protein (Fp) priming of infant and adult age mice was effective in avoiding lung histopathology, in reducing interleukin-4+ CD4 T cells and cellular infiltration of monocytes and neutrophils after RSV challenge. This study suggests that combination CpG and MPL adjuvant in RSV subunit vaccination might contribute to priming protective immune responses and preventing inflammatory RSV disease after infection.

Effect of a pneumococcal whole cell vaccine on influenza A-induced pneumococcal otitis media in infant mice

The pneumococcus remains a common cause of otitis media (OM) despite the widespread introduction of pneumococcal conjugate vaccines. In mice, a pneumococcal whole cell vaccine (WCV) induces serotype-independent protection against pneumococcal colonisation and invasive disease via TH17- and antibody-mediated immunity, respectively. We investigated the effect of WCV on influenza A-induced pneumococcal OM in an infant mouse model.C57BL/6 mice were immunised subcutaneously with a single dose of WCV or adjuvant at 6 days of age, infected with pneumococci (EF3030 [serotype 19F] or PMP1106 [16F]) at 12 days of age, and given influenza A virus (A/Udorn/72/307 [H3N2], IAV) at 18 days of age to induce pneumococcal OM. Pneumococcal density in middle ear and nasopharyngeal tissues was determined 6 and 12 days post-virus. Experiments were repeated in antibody (B6.μMT−/−)- and CD4+ T-cell-deficient mice to investigate the immune responses involved.A single dose of WCV did not prevent the development of pneumococcal OM, nor accelerate pneumococcal clearance compared with mice receiving adjuvant alone. However, WCV reduced the density of EF3030 in the middle ear at 6 days post-viral infection (p = 0.022), and the density of both isolates in the nasopharynx at 12 days post-viral infection (EF3030, p = 0.035; PMP1106, p = 0.011), compared with adjuvant alone. The reduction in density in the middle ear required antibodies and CD4+ T cells: WCV did not reduce EF3030 middle ear density in B6.μMT−/− mice (p = 0.35) nor in wild-type mice given anti-CD4 monoclonal antibody before and after IAV inoculation (p = 0.91); and WCV-immunised CD4+ T cell-deficient GK1.5 mice had higher levels of EF3030 in the middle ear than their adjuvant-immunised counterparts (p = 0.044).A single subcutaneous dose of WCV reduced pneumococcal density in the middle ears of co-infected mice in one of two strains tested, but did not prevent OM from occurring in this animal model.

S100-Alarmins are Crucial Host Factors for the Postnatal Development of Gut Homeostasis

SummaryAfter birth, the immune system experiences considerable reprogramming by interacting with the colonizing microbiota. Host factors involved in this relationship are largely unknown. Our studies in two infant cohorts and newborn mice reveal that abundant enteral S100A8/A9 trains the inflammatory and regulatory phenotype of colonic lamina propria macrophages. Neonatal S100A8/A9-alarmin deficiency results in an impaired expression of Cx3cr1, Il-10 and Tgf-β, reduced expansion of regulatory T cells, and dominant gut colonization with aerobes and facultative anaerobes, translating into a higher risk of gut dysbiosis and septic diseases preventable by one-time feeding of S100A8 at birth. Our results establish S100A8/A9 as an important host factor for developing gut homeostasis and a promising target for enteral supplementation aiming to prevent dysbiosis and associated diseases.