Introduction  Human microbiota-associated (HMA) models are used to allow in vivo studies of the human gut microbiome and its effects on host physiology. In particular, alterations in early life microbiota have been linked to allergy development during childhood. In this study, we investigated how pools of human microbiota collected from infants with different allergy risk, thrive in mice and their offspring, as well as how they influence the host metabolome.

Method  We used a two-generation HMA mouse model in which dams were colonized with human feces from three groups of infants (n = 19, samples collected during the first 8 weeks of life). In two of the groups, all infants had a strong hereditary risk for allergic disease (n = 12), but only 6 of them developed allergy before 2 years of age. In the third group, which was used as a control, none of the infants had allergic heredity or developed allergy (n = 7). Microbiota trajectories were followed from inoculation to mouse offspring, and metabolic profiles were monitored in several intestinal organs as well as in the serum of the murine offspring.

Results  The human microbiota adapted to the murine host but still presented distinct compositional features, reflecting the original inoculated samples. These microbial differences were mirrored in the mouse offspring metabolome, with group-associated patterns in sphingolipids, acylcarnitines and tryptophan metabolites. Furthermore, the metabolic profiles of the mouse offspring aligned with those observed in fecal water preparations from the corresponding human infant fecal samples.

Conclusion  Our findings highlight the significant impact of early-life microbiota on the host metabolome and show that our two-generation HMA model is suitable for studying microbiota‒metabolome relationships relevant to humans. The differences in microbiota‒metabolome correlations between individuals who develop or do not develop allergic disease suggest that an allergic predisposition might be more multifaceted than previously believed.

Hemozoin (HZ), the malaria pigment, is associated with the disease when released during the pro-inflammatory blood stage and co-infections with bacteria lead to a more severe disease progression. The underlying mechanisms are poorly understood and, here, we show that the impact of co-exposure to HZ and lipopolysaccharide (LPS) on monocyte-derived dendritic cells (moDC) alters the early transcriptional response to a subset of IFNγ controlled genes, HLA-DR, and PD-L1. HZ-exposure had no effect on inflammatory genes, which were substantially induced by LPS. The reduced expression of HLA-DR and PD-L1 by HZ was associated with the chromatin remodeling complex NuRD and a decreased binding of the NF-κB transcription factor RELA compared to cells stimulated with LPS alone. NuRD replaced the SWI/SNF complex variant PBAF at the specific promoters, without chromatin accessibility changes. The immune modulatory effect of HZ may lead to changed immune responses to bacterial co-infections.

Vγ9/Vδ2 T cells represent the largest γδ T-cell population in human blood and possess a unique responsiveness towards microbial organisms by sensing the metabolite (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP) in the context of the butyrophilin family members BTN2A1 and BTN3A1. Curiously, the bacterium Staphylococcus aureus does not produce HMB-PP but appears to be capable of inducing activation, cytokine expression and proliferation of Vγ9/Vδ2 T cells regardless, through a largely unknown mechanism. We here provide a comprehensive review of the existing literature around Vγ9/Vδ2 T-cell responses to S. aureus and discuss potential pathways, ligands and biological functions.

One-year peanut OIT in young children seems to increase gut microbiota richness and Clostridia abundance.

Plasma acylcarnitines and fatty acids follow opposite trajectories over time in OIT-treated and untreated children.

Bacterial toxins, called superantigens, are produced by Staphylococcus aureus and are known to activate γδ T cells. γδ T cells contribute to long-lasting immunity against bacterial skin infections caused by S. aureus. γδ T cells are a distinct subgroup of T cells containing the T cell receptor (TCR) γ and δ chains. The γδ TCR harbouring the variable chains TRGV9/TRDV2 is the most common TCR in human peripheral blood and is known to be activated by superantigens and are also promising candidates for tumor immunotherapy. However, detailed analyses of antigen binding to γδ TCR have been severely hampered by difficulties in producing large amounts of γδ TCR. In this study, we report a protocol to produce recombinant γδ TCR (TRGV9/TRDV2) by fusing the variable domains γδ TCR with the constant domains of αβ TCR. Subsequently, binding analyses were executed applying microscale thermophoresis showing a clear binding between superantigen and the γδ TCR in the micro molar range. In addition, the superantigen SEA was shown to induce cytokine expression in γδ T cells with moderate MHC dependence, suggesting that other receptors can act as antigen presenting molecules upon γδ T cell activation. These results pave the way towards a better understanding of superantigen recognition by the γδ T cells and facilitates the future use of γδ TCR in cellular tumor immunotherapy.

Introduction: Knowledge of IgE-verified allergy in young adults is limited as most studies are based on self-reported data. Allergic heredity is important in allergy development in early life, but less is known about the hereditary component later in life. The aim was to investigate IgE-verified and self-reported allergy and asthma at 20 years of age in association to parental allergy and environmental factors. Methods: In total, 281 individuals born into the cohort of well-characterized parents regarding allergic disease were followed to 20 years of age. The participantswere categorized by parental allergy and examined regarding allergic diseases (IgE sensitization and allergic symptoms) at 2, 5, 10, and 20 years of age. FeNO wasmeasured at 10 and 20 years. Results: In total, 45% of the study participants were allergic, with twice as many self-reported cases at age 20. Rhinitis was key to distinguishing confirmed allergy from self-reported. Having two allergic parents and increased FeNO were associated with an increased prevalence of allergic disease at 20 years. From a longitudinal perspective, rhinitis increased from childhood to young adulthood, in all heredity groups. Conclusion: In this longitudinal study, we have shown that two allergic parents as well as increased FeNO levels seem to be of importance for being allergic at 20 years old. Selfreported allergy was overreported - a result that should be considered in future survey-based reports on allergic diseases.

The aim of this study was to identify a Bifidobacterium strain that improves the performance of Limosilactobacillus reuteri DSM 17938. Initial tests showed that Bifidobacterium longum subsp. longum strains boosted the growth of DSM 17938 during in vivo-like conditions. Further characterization revealed that one of the strains, BG-L47, had better bile and acid tolerance compared to BG-L48, as well as mucus adhesion compared to both BG-L48 and the control strain BB536. BG-L47 also had the capacity to metabolize a broad range of carbohydrates and sugar alcohols. Mapping of glycoside hydrolase (GH) genes of BG-L47 and BB536 revealed many GHs associated with plant-fiber utilization. However, BG-L47 had a broader phenotypic fiber utilization capacity. In addition, B. longum subsp. longum cells boosted the bioactivity of extracellular membrane vesicles (MV) produced by L. reuteri DSM 17938 during co-cultivation. Secreted 5'-nucleotidase (5'NT), an enzyme that converts AMP into the signal molecule adenosine, was increased in MV boosted by BG-L47. The MV exerted an improved antagonistic effect on the pain receptor transient receptor potential vanilloid 1 (TRPV1) and increased the expression of the immune development markers IL-6 and IL-1ß in a peripheral blood mononuclear cell (PBMC) model. Finally, the safety of BG-L47 was evaluated both by genome safety assessment and in a human safety study. Microbiota analysis showed that the treatment did not induce significant changes in the composition. In conclusion, B. longum subsp. longum BG-L47 has favorable physiological properties, can boost the in vitro activity of L. reuteri DSM 17938, and is safe for consumption, making it a candidate for further evaluation in probiotic studies. IMPORTANCE: By using probiotics that contain a combination of strains with synergistic properties, the likelihood of achieving beneficial interactions with the host can increase. In this study, we first performed a broad screening of Bifidobacterium longum subsp. longum strains in terms of synergistic potential and physiological properties. We identified a superior strain, BG-L47, with favorable characteristics and potential to boost the activity of the known probiotic strain Limosilactobacillus reuteri DSM 17938. Furthermore, we demonstrated that BG-L47 is safe for consumption in a human randomized clinical study and by performing a genome safety assessment. This work illustrates that bacteria-bacteria interactions differ at the strain level and further provides a strategy for finding and selecting companion strains of probiotics.

Objectives: Extremely preterm (EPT; gestational week < 28 + 0, < 1000 g) neonates are vulnerable to infections and necrotising enterocolitis, important contributors to mortality and morbidity. However, knowledge regarding their immune maturation remains limited. We here investigated the longitudinal development of functional T-cell capacity in EPT infants. Methods: Peripheral blood mononuclear cells were isolated at 14th and 28th day (D) and at gestational week 36 + 0 (Gw36) from EPT infants, participated in a randomised, double-blind, placebo-controlled study of Lactobacillus reuteri DSM 17938 probiotic supplementation. Blood collected from 25 full-term (FT) infants at D14 was used as control. The secretion of immune mediators was determined through comprehensive Luminex panels after stimulation with human T-cell activator CD3/CD28 beads. Results: The levels of many mediators were low in EPT infants at D14, whereas the secretion of several chemokines was higher in EPT than in FT infants. Furthermore, Th2:Th1 cytokine ratios were higher in EPT than in FT infants. Progressively elevated secretion of, for example, IFN-γ, TNF and IL-17A in EPT infants was observed from D14 to D28 and then at Gw36. Elevated levels were observed for many proinflammatory mediators at D28. Probiotic supplementation or perinatal factors (e.g. clinical chorioamnionitis, preeclampsia and delivery mode) did not influence the cytokine and chemokine responses. Conclusions: Immune mediators induced by T-cell activation in EPT infants were mainly reduced at D14 and Th2 skewed compared to those in FT infants, but mostly recovered at Gw36, indicating immune maturation. Increased proinflammatory responses at D28 may be related to the heightened risk of severe immune-associated complications seen in EPT infants.

Background: The prevalence of peanut allergy is about 2% and mostly lifelong. Studies of oral immunotherapy (OIT) with peanut (the daily oral intake of an initially low and then increasing dose of peanut) often show problematic side effects, but there are indications of better safety and effect in younger children compared with older children and adults.

Objective: To determine the safety and effectiveness of peanut OIT with a slow up-dosing strategy and low maintenance dose in children aged 1 to 3 years who were allergic to peanut, through a 1-year interim analysis.

Method: In a randomized controlled trial (2:1 ratio), 75 children, median age 31 months (interquartile range [IQR], 23-40 months) were assigned to receive peanut OIT (n = 50) or peanut avoidance (n = 25).

Results: In the OIT and avoidance groups, 43 of 50 and 20 of 25 children, respectively, performed the 1-year open oral peanut challenge. A cumulative dose of 750 mg peanut protein after 1 year was tolerated by 72% (36 of 50 children) in the OIT group compared with 4% (1 of 25) in the avoidance group (P < .001). Median tolerated cumulative dose was 2,750 mg (IQR, 275-5,000 mg) peanut protein in the OIT group compared with 2.8 mg (IQR, 0.3-27.8 mg) in the avoidance group (P < .001). Of the doses administered at home during the first year of OIT, 1.4% resulted in adverse events and 79% were mild, and three doses of epinephrine were given at home to two individuals.

Conclusion: In children aged 1 to 3 years, peanut OIT with the combination of slow up-dosing and low maintenance dose seems safe and effective after 1 year.

Introduction: The innate branch of the immune system is important in early life, in particular for infants born preterm. Methods: We performed a longitudinal analysis of the peripheral monocyte compartment in extremely preterm children from a randomized, placebo-controlled study of probiotic supplementation. PBMCs and fecal samples were collected at several timepoints during the first months of life. Monocyte characteristics were analyzed by flow cytometry, and LPS-stimulated PBMC culture supernatants were analyzed by Luminex or ELISA. Plasma cytokines and gut microbiota composition were analyzed by ELISA and 16S rRNAsequencing, respectively. Results: The extremely preterm infants had persistent alterations in their monocyte characteristics that were further aggravated in chorioamnionitis cases. They showed a markedly reduced TLR4 expression and hampered LPS-stimulated cytokine responses 14 days after birth. Notably, at later timepoints, TLR4 expression and LPS responses no longer correlated. Sepsis during the first weeks of life strongly associated with increased proinflammatory, and reduced IL-10, responses also at postmenstrual week 36. Further, we report a correlation between gut microbiota features and monocyte phenotype and responses, but also that probiotic supplementation associated with distinct monocyte phenotypic characteristics, without significantly influencing their responsiveness. Conclusion: Extremely preterm infants have monocyte characteristics and functional features that deviate from infants born fullterm. Some of these differences persist until they reach an age corresponding to full-term, potentially making them more vulnerable to microbial exposures during the first months of life.