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Background Infections are a major cause for morbidity and mortality in neonates; however, the underling mechanisms for increased infection susceptibility are incompletely understood. Hypoxia, which is present in inflamed tissues, has been identified as an important activation signal for innate immune cells in adults and is mainly mediated by hypoxia-inducible factor 1α (HIF-1α). Fetal tissue pO2 physiologically is low but rises immediately after birth. Methods In this study, the effect of low oxygen partial pressure (pO2) on HIF-1α expression and its targets phagocytosis, reactive oxygen species (ROS) production and vascular endothelial growth factor (VEGF) secretion was compared in vitro between immune cells from adult peripheral blood and cord blood using anoxia, HIF-1α stabilizer desferroxamin (DFO) and E. coli as stimuli. Results We show that anoxia-induced HIF-1α protein accumulation, phagocytosis, ROS-production and VEGF-expression were greatly diminished in cord blood compared to adult cells. E. coli led to HIF-1α gene expression in adult and cord blood immune cells; however, cord blood cells failed to accumulate HIF-1α protein and VEGF upon E. coli stimulation. Conclusions Taken together, our results show a diminished activation of cord blood immune cells by low pO2, which might contribute to impaired reactivity in the context of infection. Impact Neonatal immune cells do not accumulate HIF-1α under low oxygen partial pressure leading to decreased phagocytosis and decreased ROS production. We demonstrate a previously unknown mechanism of reduced activation of neonatal immune cells in the context of an inflammatory response. This could contribute to the increased susceptibility of newborns and preterm infants to infection.

Background Sepsis is one of the leading causes of morbidity and mortality in the neonatal period. Compared to adults, neonates are more susceptible to infections, especially to systemic infections with Group B Streptococcus (GBS). Furthermore, neonates show defects in terminating inflammation. The immunological causes for the increased susceptibility to infection and the prolonged inflammatory response are still incompletely understood. Methods In the present study, we aimed to investigate the reaction of cord blood mononuclear cells (MNC) to stimulation with GBS in comparison to that of MNC from adult blood with focus on the proliferative response in an in vitro infection model with heat-inactivated GBS. Results We demonstrate that after stimulation with GBS the proliferation of T cells from adult blood strongly decreased, while the proliferation of cord blood T cells remained unchanged. This effect could be traced back to a transformation of adult monocytes, but not cord blood monocytes, to a suppressive phenotype with increased expression of the co-inhibitory molecule programmed death ligand 1 (PD-L1). Conclusions These results point towards an increased inflammatory capacity of neonatal MNC after stimulation with GBS. Targeting the prolonged inflammatory response of neonatal immune cells may be a strategy to prevent complications of neonatal infections. Impact Neonatal sepsis often leads to post-inflammatory complications. Causes for sustained inflammation in neonates are incompletely understood. We show that cord blood T cells exhibited increased proliferative capacity after stimulation with group B streptococci (GBS) in comparison to adult T cells. Adult monocytes but not cord blood monocytes acquired suppressive activity and expressed increased levels of PD-L1 after GBS stimulation. Increased proliferative capacity of neonatal T cells and decreased suppressive activity of neonatal monocytes during GBS infection may contribute to prolonged inflammation and development of post-inflammatory diseases in newborns.

Infection and sepsis remain among the leading causes of neonatal mortality. The susceptibility of newborns to infection can be attributed to their immature immune system. Regarding immune response, monocytes represent a numerically minor population of leukocytes. However, they contribute to a variety of immunological demands, such as continuous replenishment of resident macrophages under non-infectious conditions and migration to inflamed sites where they neutralize pathogens and secrete cytokines. Further functions include the presentation of antigens and T-cell activation. Cytokines coordinate host responses to bacterial and viral infections and orchestrate ongoing physiological signaling between cells of non-immune tissues. A critical event is the skewing of the cytokine repertoire to achieve a resolution of infection. In this regard, monocytes may hold a key position as deciders in addition to their phagocytic activity, securing the extinction of pathogens to prevent broader organ damage by toxins and pro-inflammatory reactions. Neonatal monocytes undergo various regulatory and metabolic changes. Thus, they are thought to be vulnerable in anticipating pro-inflammatory conditions and cause severe progressions which increase the risk of developing sepsis. Furthermore, clinical studies have shown that exposure to inflammation puts neonates at a high risk for adverse pulmonary, immunological and other organ developments, which may result in multiorgan disease. This review discusses significant functions and impairments of neonatal monocytes that are decisive for the outcome of bacterial infections.

Background Probiotics have a protective effect on various diseases. In neonatology, they are predominantly used to prevent necrotising enterocolitis (NEC), a severe inflammatory disease of the neonatal intestine. The mechanisms by which probiotics act are diverse; little is known about their direct effect on neonatal immune cells. Methods In this study, we investigated the effect of probiotics on the functions of neonatal monocytes in an in vitro model using three different strains (Lactobacillus rhamnosus (LR), Lactobacillus acidophilus (LA) and Bifidobacterium bifidum (BB)) and mononuclear cells isolated from cord blood. Results We show that stimulation with LR induces proinflammatory effects in neonatal monocytes, such as increased expression of surface molecules involved in monocyte activation, increased production of pro-inflammatory and regulatory cytokines and increased production of reactive oxygen species (ROS). Similar effects were observed when monocytes were stimulated simultaneously with LPS. Stimulation with LA and BB alone or in combination also induced cytokine production in monocytes, with BB showing the least effects. Conclusions Our results suggest that probiotics increase the defence functions of neonatal monocytes and thus possibly favourably influence the newborn’s ability to fight infections. Impact Probiotics induce a proinflammatory response in neonatal monocytes in vitro. This is a previously unknown mechanism of how probiotics modulate the immune response of newborns. Probiotic application to neonates may increase their ability to fight off infections.

BackgroundSepsis is one of the most important complications in preterm infants. For this reason, many such infants receive antibiotics during their hospital stay. However, early antibiotic therapy has also been associated with adverse outcome. It is yet largely unclear if the time of onset of antibiotic therapy influences the outcome. We here investigated whether the timing of initiation of antibiotic therapy plays a role in the association between antibiotic exposure and short-term outcome.MethodsRetrospective analysis of data from 1762 very low birthweight infants born in a German neonatal intensive care unit (NICU) between January 2004 and December 2021.ResultsAntibiotics were administered to 1214 of the 1762 (68.9%) infants. In 973 (55.2%) of the 1762 of infants, antibiotic therapy was initiated within the first two postnatal days. Only 548 (31.1%) infants did not have any antibiotic prescription during their stay in the NICU. Antibiotic exposure at every timepoint was associated with an increased risk of all short-term outcomes analysed in univariable analyses. In multivariable analyses, initiation of antibiotic therapy within the first two postnatal days and initiation between postnatal days 3 and 6 was independently associated with an increased risk of developing bronchopulmonary dysplasia (BPD) (OR 3.1 and 2.8), while later initiation of antibiotic therapy was not.ConclusionVery early initiation of antibiotic therapy was associated with an increased risk of BPD. Due to the study design, no conclusions on causality can be drawn. If confirmed, our data suggest that an improved identification of infants at low risk of early-onset sepsis is needed to reduce antibiotic exposure.

Newborns and especially preterm infants are much more susceptible to infections than adults. Due to immature adaptive immunity, especially innate immune cells play an important role in a newborn’s infection defense. Neonatal neutrophils exhibit profound differences in their functionality compared to neutrophils of adults. In particular, neonates possess a relevant population of suppressive neutrophils, which not only inhibit but also specifically modulate the function of T-cells. In this study, we investigated whether neonatal neutrophils are already involved in T-cell development in the thymus. For this purpose, we used a newly developed model of antibody-mediated immune cell depletion in which we administered a depleting antibody to pregnant and then lactating dams. Using this method, we were able to sufficiently deplete Ly6G-positive neutrophils in offspring. We demonstrated that the depletion of neutrophils in newborn mice resulted in altered peripheral T-cell homeostasis with a decreased CD4+/CD8+ T-cell ratio and decreased expression of CD62L. Neutrophil depletion even affected T-cell development in the thymus, with increased double positive thymocytes and a decreased CD4+/CD8+ single positive thymocyte ratio. Altogether, we demonstrated a previously unknown mechanism mediating neutrophils’ immunomodulatory effects in newborns.

For almost nearly a century, memory functions have been attributed only to acquired immune cells. Lately, this paradigm has been challenged by an increasing number of studies revealing that innate immune cells are capable of exhibiting memory-like features resulting in increased responsiveness to subsequent challenges, a process known as trained immunity (known also as innate memory). In contrast, the refractory state of endotoxin tolerance has been defined as an immunosuppressive state of myeloid cells portrayed by a significant reduction in the inflammatory capacity. Both training as well tolerance as adaptive features are reported to be accompanied by epigenetic and metabolic alterations occurring in cells. While training conveys proper protection against secondary infections, the induction of endotoxin tolerance promotes repairing mechanisms in the cells. Consequently, the inappropriate induction of these adaptive cues may trigger maladaptive effects, promoting an increased susceptibility to secondary infections—tolerance, or contribute to the progression of the inflammatory disorder—trained immunity. This review aims at the discussion of these opposing manners of innate immune and non-immune cells, describing the molecular, metabolic and epigenetic mechanisms involved and interpreting the clinical implications in various inflammatory pathologies.

Neonatal sepsis is a leading cause of neonatal morbidity and mortality, associated with immunosuppression. Myeloid-derived suppressor cells (MDSCs) are cells with immunosuppressive activity, present in high amounts in cord blood. Mechanisms regulating MDSC expansion are incompletely understood. Adenosine is a metabolite with immunoregulatory effects that are elevated in cord blood.Impact of adenosine on peripheral and cord blood mononuclear cells (PBMCs and CBMCs) was analysed by quantification of ectonucleotidases and adenosine receptor expression, MDSC induction from PBMCs and CBMCs, their suppressive capacity on T cell proliferation and effector enzyme expression by flow cytometry.Cord blood monocytes mainly expressed CD39, while cord blood T cells expressed CD73. Adenosine-induced MDSCs from PBMCs induced indoleamine-2,3-dioxygenase (IDO) expression and enhanced arginase I expression in monocytes. Concerted action of IDO and ArgI led to effective inhibition of T cell proliferation. In addition, adenosine upregulated inhibitory AAdenosine acts by inducing MDSCs and upregulating inhibitory AImmune effector cells, that is, monocytes, T cells and MDSCs from cord blood express ectonucleotidases CD39 and CD73 and may thus serve as a source for adenosine as an immunomodulatory metabolite. Adenosine mediates its immunomodulatory properties in cord blood by inducing MDSCs, and by modulating the inhibitory adenosine A

Background Sepsis is one of the most important complications in preterm infants. For this reason, most preterm infants receive antibiotics during their first postnatal week. Since 2013, a weekly colonization screening has been installed in German neonatal intensive care units (NICUs), including multi-drug resistant organisms (MDRO) and pathogens with increased epidemic potential. We here investigated the impact of early antibiotic exposure on the colonization with these pathogens. Methods Data from 1407 preterm infants with gestational age Results Antibiotics were administered to 911/1407 (64.7%) participating infants during their first postnatal week. Screening-targeted pathogens were detected in 547/1407 (38.9%). Early antibiotic exposure did not increase the risk of colonization with screening-targeted pathogens. The only independent risk factor for colonisation with potential pathogens was the admitting hospital. Interestingly, longer antibiotic therapy (> 7 days) decreased the risk for acquiring pathogens with increased epidemic potential. Conclusion Early antibiotic exposure did not impact the risk for colonization with MDRO or highly epidemic pathogens in preterm infants. Further studies are needed to identify risk factors for the acquisition of MDRO and highly epidemic pathogens and potential associations with long-term outcome.

Immunologic research 71(2), 185-196 (2023). doi:10.1007/s12026-022-09340-6, Published by Humana Press, Totowa, NJ

The study aims to investigate the attitudes of medical students regarding the importance and relevance of vaccinations, whether vaccinations should be compulsory and how to employ a new teaching concept to deal with vaccination-critical parents.This mixed-method study consists of a quantitative questionnaire and focus groups. Quantitative data were analysed by calculating the descriptive statistics, and interviews were analysed using Mayring's content analysis.A total of 170 medical students completed the questionnaire, and 59 students participated in 9 focus groups. Students reported that they felt more confident dealing with vaccination-critical parents after learning the new teaching concept. Similar results were found for medical students prior to and during the pandemic. During the pandemic, medical students viewed vaccinations for several diseases, such as measles or COVID-19, as important (range: M = 3.56, SD = 0.54 to M = 3.97, SD = 0.17). Similar results were found for medical students prior to the pandemic (range: M = 3.26, SD = 0.77 to M = 3.94, SD = 0.24). In the focus groups, however, medical students displayed controversial attitudes regarding compulsory vaccinations.While the medical students agreed on the use of vaccination for highly infectious diseases, their level of agreement decreased depending on the severity of the disease. Practical recommendations that come out of the study are creating a trustful relationship with and delivering information to patients.

During pregnancy, maternal immune system has to balance tightly between protection against pathogens and tolerance towards a semi-allogeneic organism. Dysfunction of this immune adaptation can lead to severe complications such as pregnancy loss, preeclampsia or fetal growth restriction. In the present study we analyzed the impact of the murine MHC class Ib molecule Qa-2 on pregnancy outcome in vivo. We demonstrate that lack of Qa-2 led to intrauterine growth restriction and increased abortion rates especially in late pregnancy accompanied by a disturbed trophoblast invasion and altered spiral artery remodeling as well as protein aggregation in trophoblast cells indicating a preeclampsia-like phenotype. Furthermore, lack of Qa-2 caused imbalanced immunological adaptation to pregnancy with altered immune cell and especially T-cell homeostasis, reduced Treg numbers and decreased accumulation and functional activation of myeloid-derived suppressor cells. Lastly, we show that application of sHLA-G reduced abortion rates in Qa-2 deficient mice by inducing MDSC. Our results highlight the importance of an interaction between HLA-G and MDSC for pregnancy success and the therapeutic potential of HLA-G for treatment of immunological pregnancy complications.

Neonatal sepsis is a leading cause of perinatal morbidity and mortality. In comparison to adults, neonates exhibit a higher susceptibility to infections. Myeloid-derived suppressor cells (MDSCs) are myeloid cells with suppressive activity on other immune cells accumulating during foetal life and controlling inflammation in neonates. Most studies investigating the mechanisms for MDSC-mediated immune suppression have been focused on T-cells. Thus far, little is known about the role of MDSC for monocyte function. The impact of human cord blood MDSCs (CB-MDSCs) on monocytes was investigated in an in vitro model. CB-MDSCs were co-cultured with peripheral blood mononuclear cells and monocytes were analysed for expression of surface markers, T cell stimulatory and phagocytic capacity, as well as the production of intracellular cytokines by flow cytometry. CB-MDSCs increased the expression of co-inhibitory molecules and decreased the expression of major histocompatibility complex class II molecules on monocytes, leading to an impaired T-cell stimulatory capacity. Upon bacterial stimulation, expression of phagocytosis receptors, phagocytosis rates and production of tumor necrosis factor-α by monocytes was diminished by CB-MDSCs. We show that CB-MDSCs profoundly modulate monocyte functions, thereby indirectly impairing T-cell activation. Further research is needed to figure out if MDSCs could be a therapeutic target for inflammatory diseases in neonates like neonatal sepsis.

BACKGROUND Sepsis is a major cause of death in neonates. Knowledge about epidemiology, risk factors, causative pathogens and outcome of neonatal sepsis is important to improve neonatal care. For Germany, only few data on neonatal sepsis in very low birth weight (VLBW) infants exist. METHODS Data from 14,926 preterm infants with birth weight

Background In 2013 German infection surveillance guidelines recommended weekly colonization screening for multidrug-resistant (MDRO) or highly epidemic organisms for neonatal intensive care units (NICUs) and extended hygiene measures based on screening results. It remains a matter of debate whether screening is worth the effort. We therefore aimed to evaluate sepsis related outcomes before and after the guideline update. Methods The German Neonatal Network (GNN) is a prospective cohort study including data from extremely preterm infants between 22 + 0 and 28 + 6 gestational weeks born in 62 German level III NICUs. Results Infants treated after guideline update (n = 8.903) had a lower mortality (12.5% vs. 13.8%, p = 0.036), reduced rates for clinical sepsis (31.4 vs. 42.8%, p p = 0.003) as compared to infants treated before update (n = 3.920). In a multivariate logistic regression analysis, nine pathogens of culture-proven sepsis were associated with sepsis-related death, e.g. Pseudomonas aeruginosa [OR 59 (19–180), p p p Conclusions The introduction of weekly screening and extended hygiene measures is associated with reduced sepsis rates, but has no effects on sepsis-related mortality and sepsis with screening-relevant pathogens. The high exposure rate to meropenem should be a target of antibiotic stewardship programs.

Neutrophils, as the first cellular line of innate host defense, employ phagocytosis and formation of neutrophil extracellular traps (NETs) to combat infections. Classical NET formation induced by phorbol myristate acetate requires several hours to complete. However, recent studies demonstrated rapid NET formation in neutrophils upon stimulation by platelets, Staphylococcus aureus or fungal products. Here we describe that antibody- or complement-induced phagocytosis triggers rapid NET formation. In contrast to classical NETosis, chemical inhibition of NADPH oxidase as well as using NADPH oxidase-deficient patient neutrophils did not affect rapid NET formation. Although phagocytosis and rapid NET formation may not be the prerequisite of each other, cooperation of phagocytosis and rapid NET formation may be essential to improve the efficiency of defense mechanisms in combating disseminating bacteria. Dissecting the differential mechanisms of NET formation is crucial to develop novel therapeutic strategies for infectious and auto-immune diseases where NETs play an essential role.

Summary Extracorporeal photopheresis (ECP) is a widely used immunomodulatory therapy for the treatment of various T cell-mediated disorders such as cutaneous T cell lymphoma (CTCL), graft-versus-host disease (GvHD) or systemic sclerosis. Although clinical benefits of ECP are already well described, the underlying mechanism of action of ECP is not yet fully understood. Knowledge on the fate of CD14+ monocytes in the context of ECP is particularly limited and controversial. Here, we investigated the immunoregulatory function of ECP treated monocytes on T cells in an in-vitro ECP model. We show that ECP-treated monocytes significantly induce proinflammatory T cell types in co-cultured T cells, while anti-inflammatory T cells remain unaffected. Furthermore, we found significantly reduced proliferation rates of T cells after co-culture with ECP-treated monocytes. Both changes in interleukin secretion and proliferation were dependent on cell-contact between monocytes and T cells. Interestingly, blocking interactions of programmed death ligand 1 (PD-L1) to programmed death 1 (PD-1) in the in-vitro model led to a significant recovery of T cell proliferation. These results set the base for further studies on the mechanism of ECP, especially the regulatory role of ECP-treated monocytes.

SUMMARY Preterm delivery is the leading cause of perinatal morbidity and mortality. Among the most important complications in preterm infants are peri- or postnatal infections. Myeloid-derived suppressor cells (MDSC) are myeloid cells with suppressive activity on other immune cells. Emerging evidence suggests that granulocytic MDSC (GR-MDSC) play a pivotal role in mediating maternal-foetal tolerance. The role of MDSC for postnatal immune-regulation in neonates is incompletely understood. Until now, nothing is known about expression of MDSC in preterm infants. In the present pilot study, we quantified GR-MDSC counts in cord blood and peripheral blood of preterm infants born between 23 + 0 and 36 + 6 weeks of gestation (WOG) during the first three months of life and analysed the effect of perinatal infections. We show that GR-MDSC are increased in cord blood independent of gestational age and remain elevated in peripheral blood of preterm infants during the neonatal period. After day 28 they drop to nearly adult levels. In case of perinatal or postnatal infection, GR-MDSC further accumulate and correlate with inflammatory markers C-reactive protein (CRP) and white blood cell counts (WBC). Our results point towards a role of GR-MDSC for immune-regulation in preterm infants and render them to a potential target for cell-based therapy of infections in these patients. This article is protected by copyright. All rights reserved.

Purpose The optimal surgical management of extremely (ELBW) and very low-birth-weight (VLBW) neonates with esophageal atresia and distal tracheoesophageal fistula (EA/TEF) (Gross type C) is still debated. The aim of this study was to evaluate the surgical outcome of primary repair in these patients and compare it to ≥1500g neonates. Methods Medical records of neonates with repaired EA from 2002 to 2016 were reviewed. Results 4 ELBW, 7 VLBW, and 24 ≥1500g infants had type C EA/TEF and underwent primary repair. Anastomotic leakage occurred in 0% ELBW, 0% VLBW and 8.3% ≥1500g patients and anastomotic stricture in 25% ELBW, 28.5% VLBW and 37.5% ≥1500g patients. 50% ELBW, 14.2% VLBW and 20.8% ≥1500g patients underwent secondary fundoplication. One patient of the VLBW group and one patient of the ≥1500g group died postoperatively of causes not related to EA/TEF. Conclusions In extremely and very low-birth-weight neonates with type C EA/TEF surgical outcome after primary repair is comparable to the outcome in ≥1500g neonates. Primary repair can be performed in most of these patients and staged repair can be restricted to unstable patients. Level of evidence Treatment study level III.

Infections are a leading cause of perinatal morbidity and mortality. The outstandingly high susceptibility to infections early in life is mainly attributable to the compromised state of the neonatal immune system. One important difference to the adult immune system is a bias towards T helper type 2 (Th2) responses in newborns. However, mechanisms regulating neonatal T‐cell responses are incompletely understood. Granulocytic myeloid‐derived suppressor cells (GR‐MDSC) are myeloid cells with a granulocytic phenotype that suppress various functions of other immune cells and accumulate under physiological conditions during pregnancy in maternal and fetal blood. Although it has been hypothesized that GR‐MDSC accumulation during fetal life could be important for the maintenance of maternal–fetal tolerance, the influence of GR‐MDSC on the immunological phenotype of neonates is still unclear. Here, we investigated the impact of GR‐MDSC isolated from cord blood (CB‐MDSC) on the polarization of Th cells. We demonstrate that CB‐MDSC inhibit Th1 responses and induced Th2 responses and regulatory T (Treg) cells. Th1 inhibition was cell‐contact dependent and occurred independent of other cell types, while Th2 induction was mediated independently of cell contact through expression of ArgI and reactive oxygen species by CB‐MDSC and partially needed the presence of monocytes. Treg cell induction by CB‐MDSC also occurred cell‐contact independently but was partially mediated through inducible nitric oxide synthase. These results point towards a role of MDSC in regulating neonatal immune responses. Targeting MDSC function in neonates could be a therapeutic opportunity to improve neonatal host defence.

Susceptibility to infection during the neonatal period and reduced control of inflammation in neonates are attributed to immunosuppression persisting from fetal life. Myeloid-derived suppressor cells (MDSCs) are immature myeloid progenitors with suppressive activity and increased numbers in cord blood. We hypothesized that MDSCs contribute to innate host defence in neonates, paralleled by anti-inflammatory signalling.Phagocytic activity, infection induced apoptosis, expression of B-cell lymphoma (Bcl)-2 family proteins, production of reactive oxygen species (ROS), cytokine production and T-cell suppression of neonatal granulocytic-MDSCs (G-MDSCs) after infection with Escherichia coli (E. coli) were compared to neonatal autologous mature polymorphonuclear leukocytes (PMNs). Phagocytic activity of G-MDSCs upon infection with E. coli was equal to that of mature PMNs, however, apoptosis of G-MDSCs was decreased. G-MDSCs showed enhanced Bcl-2-expression and lower ROS production compared to PMNs. Inhibition of Bcl-2 reduced apoptosis rates of G-MDSCs to that of mature PMNs. Induction of anti-inflammatory transforming growth factor beta (TGF-β) was enhanced, while pro-inflammatory IL-8 decreased in G-MDSCs compared to PMNs. Infected G-MDSCs strongly suppressed proliferation of T cells. We show a direct role of G-MDSCs for anti-bacterial host defence. Prolonged survival and anti-inflammatory capacity suggest that G-MDSCs are important for immune-regulation after bacterial infection.

Establishing and maintaining maternal-fetal tolerance is essential for a successful pregnancy; failure of immunological adaptation to pregnancy leads to severe complications such as abortion or preterm delivery. Myeloid-derived suppressor cells (MDSCs) are innate immune cells that suppress T-cell responses, expand during pregnancy and thus may play a role in tolerance induction. Human leucocyte antigen G (HLA-G) is a major histocompatibility complex (MHC) I molecule with immune-modulatory properties, which is expressed during pregnancy. Here, we investigated the impact of HLA-G on MDSCs accumulation and activation in pregnant women. We demonstrate that granulocytic MDSCs (GR-MDSCs) express receptors for HLA-G, namely immunoglobulin-like transcript (ILT) 2 and 4, and that ILT4-expression by GR-MDSCs is regulated during pregnancy. Stimulation with soluble HLA-G (sHLA-G) increased suppressive activity of GR-MDSCs, induced MDSCs from peripheral blood mononuclear cells (PBMCs) and led to phosphorylation of the signal transducer and activator of transcription 3 (STAT3) and induction of indoleamine-2,3-dioxygenase (IDO) in myeloid cells. Effects of sHLA-G on MDSC accumulation were mediated through ILT4. These results suggest an interaction between MDSCs and HLA-G in humans as a potential mechanism for maintaining maternal-fetal tolerance. Modulating MDSC function during pregnancy via HLA-G might provide new opportunities for a therapeutic manipulation of immunological pregnancy complications.

Background: Hypoxemia and bradycardia occur frequently in preterm infants, but are incompletely understood. They are more prevalent during infections and following immunization. Data on adults suggested an increased immune response if subjects slept following vaccination, suggesting an interaction between circadian rhythm and the immune system. Whether this holds true for preterm infants with their less well-established circadian rhythm is unclear. Objective: Do infants born at 26–30 weeks’ gestation and having received their first routine hexavalent vaccination in the morning have a lower cardiorespiratory event rate (CER) after vaccination than those receiving it in the evening? Methods: Twenty-six infants were randomized to an evening versus morning vaccination group in a pilot and main study with 10 and 16 participants, respectively. Pulse oximeter saturation, actigraphy, and rectal temperature were obtained for 24 h before and after vaccination. Blood samples for vaccination titers were taken before vaccination and during a follow-up examination in our outpatient clinic; another blood sample was taken 24 h after vaccination to determine inflammatory markers. Results: Vaccination led to an increase in CER in both groups, but there was no difference in CER between the morning and evening groups. Vaccination titers for Bordetella pertussis were increased in both groups, with no difference in inflammatory markers 24 h after vaccination. Body temperature increased in both groups after vaccination. Participants in the evening group slept longer after vaccination. Conclusions: We did not identify a difference in CER between morning and evening vaccination but could confirm increased body temperatures and vaccination titers following vaccination.

Immunological pregnancy complications are a main challenge in reproductive medicine. Mechanisms regulating the adaptation of the maternal immune system to pregnancy are incompletely understood and therapeutic options limited. Myeloid derived suppressor cells (MDSC) are immune-modulatory cells expanding during healthy pregnancy and seem to play a crucial role for maternal-fetal tolerance. Recent studies showed that exosomes produced by MDSC have immune-modulatory effects corresponding to their parental cells under different pathological conditions. Here, we investigated immunological effects of exosomes of GR-MDSC during pregnancy. Isolated GR-MDSC exosomes from peripheral blood of pregnant women were tested for functionality in different in vitro assays. We show that GR-MDSC exosomes exhibited profound immune-modulatory effects such as suppression of T-cell proliferation, T helper 2 (Th2)-cell polarization, induction of regulatory T-cells and inhibition of lymphocyte cytotoxicity. Our results confirm that MDSC-derived exosomes functionally correspond to their parental cells and identify them as an interesting therapeutic target for immunological pregnancy complications.

Summary The predisposition of preterm neonates to invasive infection is, as yet, incompletely understood. Regulatory T cells (Tregs) are potential candidates for the ontogenetic control of immune activation and tissue damage in preterm infants. It was the aim of our study to characterize lymphocyte subsets and in particular CD4+CD25+forkhead box protein 3 (FoxP3)+ Tregs in peripheral blood of well-phenotyped preterm infants (n = 117; 23 + 0 – 36 + 6 weeks of gestational age) in the first 3 days of life in comparison to term infants and adults. We demonstrated a negative correlation of Treg frequencies and gestational age. Tregs were increased in blood samples of preterm infants compared to term infants and adults. Notably, we found an increased Treg frequency in preterm infants with clinical early-onset sepsis while cause of preterm delivery, e.g. chorioamnionitis, did not affect Treg frequencies. Our data suggest that Tregs apparently play an important role in maintaining maternal-fetal tolerance, which turns into an increased sepsis risk after preterm delivery. Functional analyses are needed in order to elucidate whether Tregs have potential as future target for diagnostics and therapeutics.

BACKGROUNDBetween 2010 and 2012, 3 outbreaks of nosocomial infections in German neonatal intensive care units (NICUs) attracted considerable public interest. Headlines on national television channels and in newspapers had important consequences for the involved institutions and a negative impact on the relationship between families and staff in many German NICUs.OBJECTIVETo determine whether NICU outbreaks reported in the media influenced provider behavior in the community of neonatal care and led to more third-line antibiotic prescribing.DESIGNObservational cohort study.METHODSTo investigate secular trends, we evaluated data for very-low-birth-weight infants (VLBWIs, birth weight RESULTSThe exposure of all VLBWIs to third-line antibiotics increased after outbreaks (19.4% before vs 22.5% after; P=.007). This trend particularly affected male infants (4.6% increase; P=.005) and infants with a birth weight between 1,000 and 1,499 g (3.5% increase; P=.001)In a logistic regression analysis, month of discharge as linear variable of time was associated with increased exposure to third-line antibiotics (odds ratio [OR], 1.01; 95% confidence interval [CI], 1.009–1.014; PP=.024).CONCLUSIONSMedia reports directly affect medical practice, eg, overuse of third-line antibiotics. Future communication and management strategies must be based on objective dialogues between the scientific community and investigative journalists.Infect Control Hosp Epidemiol 2016;37:924–930

BACKGROUND NOD2 loss-of-function mutations, that is, R702W [rs2066844], G908R [rs2066845], and Leu1007fsinsC [rs5743293], have been linked to inflammatory bowel diseases. It is yet unknown whether these variants are also associated with necrotizing enterocolitis (NEC) or focal intestinal perforation (FIP) in infants of very low birth weight (VLBW). METHODS To test this hypothesis, we genotyped 9082 VLBW infants with European ancestry enrolled in a prospective, population-based cohort study of the German Neonatal Network. We assessed the effect of the NOD2 gene variants on the risk for major morbidities of the gastrointestinal tract, that is, NEC/FIP requiring surgery in multivariable logistic regression analyses. RESULTS In the whole cohort of VLBW infants, carriers of ≥ 2 NOD2 variant alleles had an increased risk for NEC requiring surgery (odds ratio [OR], 3.57; 95% confidence interval [CI], 1.27-10.04; P = 0.03) and NEC or FIP requiring surgery (OR, 3.81; 95% CI, 1.70-8.51; P = 0.004) as compared with wild-type genotypes. In a multivariable logistic regression analysis including gestational age, birth weight, gender, multiple birth, and inborn delivery, the association between ≥ 2 NOD2 variant alleles and NEC surgery (OR, 4.14; 95% CI, 1.41-12.12; P = 0.009), FIP surgery (OR, 3.50; 95% CI, 1.02-12.04; P = 0.047), and NEC or FIP surgery (OR, 4.10; 95% CI, 1.74-9.73; P = 0.001) proved to be independent. We also performed a regression analysis in the subgroup of infants with available information on Lactobacillus acidophilus/Bifidobacterium infantis probiotic supplementation (n = 3638). Although probiotics had a protective effect on NEC and NEC or FIP requiring surgery, the NOD2 variants had no significant impact in this subgroup. CONCLUSIONS VLBW infants carrying ≥ 2 NOD2 genetic risk factors of inflammatory bowel disease in adults have an increased risk for severe gastrointestinal complications, such as NEC requiring surgery. Therefore, infants might benefit from NOD2 genotyping followed by supplementation with probiotics. Replication studies are needed along with genome-wide arrays to allow risk-adapted prevention and therapeutic strategies.

Graft-versus-host disease (GvHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. However, the pathophysiology of GvHD remains poorly understood. In this study, we analyzed the induction of Th17 cells by monocytes of patients with GvHD in vitro, demonstrating that monocytes isolated from patients with acute skin and intestinal GvHD stage I–IV and chronic GvHD induce significantly increased levels of Th17 cells compared with patients without GvHD. S100 proteins are known to act as innate amplifier of inflammation. We therefore investigated the presence of S100 proteins in the stool, serum, and bowel tissue of patients with GvHD and the influence of S100 proteins on the induction of Th17 cells. Elevated levels of S100 proteins could be detected in patients with acute GvHD, demonstrating the release of these phagocyte-specific proteins during GvHD. Furthermore, stimulation of monocytes with S100 proteins was found to promote Th17 development, emphasizing the role of S100 proteins in Th17-triggered inflammation. Altogether, our results indicate that induction of Th17 cells by activated monocytes and the stimulatory effects of proinflammatory S100 proteins might play a relevant role in the pathogenesis of acute GvHD. Regarding our data, S100 proteins might be novel markers for the diagnosis and follow-up of GvHD.

Immune tolerance toward the semiallogeneic fetus plays a crucial role in the maintenance of pregnancy. Myeloid-derived suppressor cells (MDSCs) are innate immune cells characterized by their ability to modulate T-cell responses. Recently, we showed that MDSCs accumulate in cord blood of healthy newborns, yet their role in materno-fetal tolerance remained elusive. In the present study, we demonstrate that MDSCs with a granulocytic phenotype (GR-MDSCs) are highly increased in the peripheral blood of healthy pregnant women during all stages of pregnancy compared with nonpregnant controls, whereas numbers of monocytic MDSCs were unchanged. GR-MDSCs expressed the effector enzymes arginase-I and iNOS, produced high amounts of ROS and efficiently suppressed T-cell proliferation. After parturition, GR-MDSCs decreased within a few days. In combination, our results show that GR-MDSCs expand in normal human pregnancy and may indicate a role for MDSCs in materno-fetal tolerance.

Background: Cleaving ligands and receptors of the tumor necrosis factor (TNF) superfamily can critically regulate the induction of apoptosis. Matrix metalloproteinases (MMPs) such as MMP-9 and tumor necrosis factor-&alpha, converting enzyme (TACE) have been shown to cleave CD95-Ligand (CD95L) and TNF/(TNF receptor-1) TNFR1 which induce phagocytosis induced cell death (PICD) in adult monocytes. This process is reduced in neonatal monocytes. Methods: Here we tested in vitro, whether Escherichia coli infection mounts for activation of MMP-9 and TACE in monocytes and whether this process regulates PICD. Results: The surface expression of TACE was most prominent on infected adult monocytes. In contrast, surface presentation of MMP-9 was highest on infected neonatal monocytes. Selective blocking of MMP-9 decreased CD95L secretion, while inhibition of TACE left CD95L secretion unaltered. Blocking of MMP-9 increased surface CD95L (memCD95L) expression on infected neonatal monocytes to levels comparable to infected adult monocytes. Moreover, MMP-9 inhibition raised PICD of infected neonatal monocytes to levels observed for infected adult monocytes. In contrast, TACE inhibition decreased PICD in infected monocytes. Addition of extracellular TNF effectively induced memCD95L presentation and PICD of adult monocytes and less of neonatal monocytes. Conclusion: MMP-9 activity is crucial for downregulating cell-contact dependent PICD in E. coli infected neonatal monocytes. By this mechanism, MMP-9 could contribute to reducing sustained inflammation in neonates.

Summary Neonates show an impaired anti-microbial host defence, but the underlying immune mechanisms are not understood fully. Myeloid-derived suppressor cells (MDSCs) represent an innate immune cell subset characterized by their capacity to suppress T cell immunity. In this study we demonstrate that a distinct MDSC subset with a neutrophilic/granulocytic phenotype (Gr-MDSCs) is highly increased in cord blood compared to peripheral blood of children and adults. Functionally, cord blood isolated Gr-MDSCs suppressed T cell proliferation efficiently as well as T helper type 1 (Th1), Th2 and Th17 cytokine secretion. Beyond T cells, cord blood Gr-MDSCs controlled natural killer (NK) cell cytotoxicity in a cell contact-dependent manner. These studies establish neutrophilic Gr-MDSCs as a novel immunosuppressive cell subset that controls innate (NK) and adaptive (T cell) immune responses in neonates. Increased MDSC activity in cord blood might serve as key fetomaternal immunosuppressive mechanism impairing neonatal host defence. Gr-MDSCs in cord blood might therefore represent a therapeutic target in neonatal infections.

We performed an observational study with very-low-birth weight infants (VLBWI) ≤33 weeks of gestation born in centers of the German Neonatal Network (GNN; (total n = 8534, n = 6229 received probiotics). The primary objectives of our study were (a) to assess the effect of Lactobacillus acidophilus/Bifidobacterium infantis probiotics on growth in VLBWI during primary stay in hospital and (b) to determine whether this effect is modified by antibiotic exposure. In linear regression models the administration of probiotics was independently associated with improved weight gain [g/d; effect size B = 0.62 (95% CI: 0.37–0.87), p

Prenatal exposure to parasite antigens or allergens will influence the profile and strength of postnatal immune responses, such contact may tolerize and increase susceptibility to future infections or sensitize to environmental allergens. Exposure in utero to parasite antigens will distinctly alter cellular gene expression in newborns. Gene microarrays were applied to study gene expression in umbilical cord blood cell (UCBC) from parasite-exposed (Para-POS) and non-exposed (Para-NEG) neonates. UCBC were activated with antigens of helminth (Onchocerca volvulus), amoeba (Entamoeba histolytica) or allergens of mite (Dermatophagoides farinae). When UCBC from Para-POS and Para-NEG newborns were exposed to helminth antigens or allergens consistent differences occurred in the expression of genes encoding for MHC class I and II alleles, signal transducers of activation and transcription (STATs), cytokines, chemokines, immunoglobulin heavy and light chains, and molecules associated with immune regulation (SOCS, TLR, TGF), inflammation (TNF, CCR) and apoptosis (CASP). Expression of genes associated with innate immune responses were enhanced in Para-NEG, while in Para-POS, the expression of MHC class II and STAT genes was reduced. Within functional gene networks for cellular growth, proliferation and immune responses, Para-NEG neonates presented with significantly higher expression values than Para-POS. In Para-NEG newborns, the gene cluster and pathway analyses suggested that gene expression profiles may predispose for the development of immunological, hematological and dermatological disorders upon postnatal helminth parasite infection or allergen exposure. Thus, prenatal parasite contact will sensitize without generating aberrant inflammatory immune responses, and increased pro-inflammatory but decreased regulatory gene expression profiles will be present in those neonates lacking prenatal parasite antigen encounter.

Background: Immunoglobulins (IVIG) have been shown to be useful in adults suffering from sepsis. In contrast, prophylactic and curative IVIG trials failed to show beneficial effects in neonates. We tested the hypothesis that IVIG, have different effects on monocytes from cord blood (CBMO) and peripheral blood monocytes from adults (PBMO) with respect to survival, phenotype, and function. Methods: Mononuclear cells, or purified monocytes, were cultured in 5% human serum, incubated with polyvalent IVIG (1 mg/ml), stimulated with green fluorescent protein (GFP)-labeled Escherichia coli (E. Coli-GFP), Interferon-c (IFN-c, 50 U/ml), or the T cell mitogen anti-CD3 monoclonal antibody, aCD3-mAb, (5 lg/ml). Phagocytosis, phenotype, T cell proliferation, and apoptosis were assessed by flow cytometry. Results: IVIG enhanced phagocytosis in PBMO or CBMO when infected directly after isolation, while IVIG had no effect on monocytes cultured 48 h prior to infection. In contrast to PBMO, IVIG inhibited the IFN-c mediated up-regulation of CD80, CD86, and HLA-DR on CBMO. In the presence of IVIG, stimulation with aCD3 in cord blood enhanced deletion, inhibited blast formation and CD28 up-regulation of T cells (P < 0.05 vs. T cells from adults). IVIG induced monocyte apoptosis, associated with up-regulation of Annexin V and loss of nuclear DNA, which was more pronounced in CBMO. Although phagocytosis induced cell death (PICD) was lower in CBMO (P < 0.05 vs. PBMO), the addition of IVIG enhanced PICD levels of CBMO to the extent of PBMO. Conclusions: IVIG inhibits co-stimulatory receptors and functions of CBMO and induces apoptosis. These findings may be of clinical relevance for the failure of IVIG benefit in neonatal sepsis. V C 2011

Kurzfassung Zur nachhaltigen Sicherung von Wettbewerbsvorteilen in einem zunehmend turbulenten Umfeld wird eine wandlungsfähige Unternehmensausrichtung gefordert. Insbesondere das verarbeitende Gewerbe, wie z.B. der Fahrzeug- und Maschinenbau, sieht sich dabei der Herausforderung ausgesetzt, den Auftragsabwicklungsprozess an sich wandelnde Anforderungen anzupassen. Für die Auswahl der richtigen Maßnahmen ist allerdings zunächst die Kenntnis über die tatsächlich relevanten Wandlungstreiber und deren Auswirkungen notwendig. Anhand der in diesem Beitrag beschriebenen Vorgehensweise kann in Unternehmen eine systematische Identifikation, Bewertung und Prognose von Wandlungstreibern durchgeführt werden.

Allogeneic hematopoietic stem cell transplantation represents the most effective form of immunotherapy for chemorefractory diseases. However, animal models have been missing that allow evaluation of donor-patient–specific graft-versus-leukemia effects. Thus, we sought to establish a patient-tailored humanized mouse model that would result in long-term engraftment of various lymphocytic lineages and would serve as a donor-specific surrogate. Following transfer of donor-derived peripheral blood stem cells into NOD/SCID/IL-2Rγnull (NSG) mice with supplementation of human IL-7, we could demonstrate robust engraftment and multilineage differentiation comparable to earlier studies using cord blood stem cells. Phenotypical and functional analyses of lymphoid lineages revealed that >20 wk posthematopoietic stem cell transplantation, the majority of T lymphocytes consisted of memory-type CD4+ T cells capable of inducing specific immune functions, whereas CD8+ T cells were only present in low numbers. Analysis of NSG-derived NK cells revealed the expression of constitutively activated CD56brightCD16− killer Ig-like receptornegative NK cells that exhibited functional impairments. Thus, the data presented in this study demonstrate that humanized NSG mice can be successfully used to develop a xenotransplantation model that might allow patient-tailored treatment strategies in the future, but also highlight the need to improve this model, for example, by coadministration of differentiation-promoting cytokines and induction of human MHC molecules to complement existing deficiencies in NK and CD8+ T cell development.

Phagocytosis of apoptotic cells, e.g., neutrophils, by monocytes is essential for resolution of inflammation. Delayed removal leads to secondary necrosis, perpetuating inflammation, and tissue destruction. Common histologic features in neonatal chronic inflammatory disorders are an accumulation of apoptotic cells in inflamed tissues. We hypothesized that apoptotic cell removal by monocytes is compromised in newborns. PKH-26 labeled autologous or allogeneic apoptotic neutrophils were fed to monocytes of adult donors (PBMO) and cord blood (CBMO), and phagocytic activity was analyzed by flow cytometry and confocal microscopy. Relative mRNA-expression levels of 21 surface receptors and bridging molecules relevant for apoptotic cell removal were measured, as was postphagocytic IL-8 production upon LPS-stimulation. Compared with PBMO, CBMO exhibited a significantly diminished phagocytotic competence for autologous and allogeneic apoptotic neutrophils. mRNA-expression levels of milk fat globule-EGF factor 8 and T cell immunoglobulin- and mucin-domain-containing molecule, two crucial members of the phagocytic synapse of apoptotic cell removal, were reduced in CBMO. In PBMO, interaction with autologous apoptotic neutrophils reduced LPS-induced IL-8 production whereas it was enhanced in CBMO. Our data suggest a specific defect in CBMO during clearance of apoptotic neutrophils resulting in impaired anti-inflammatory capacity.

An imbalance in apoptosis or survival of immune cells plays an essential role in the pathophysiology of sepsis. Phagocytosis-induced cell death (PICD) is a common result of the pathogen-host cell interaction mediated by reactive oxygen species (ROS). Neonatal sepsis is frequently characterized by hyperinflammation. Cord blood monocytes (CBMO) are equivalent to monocytes of adults [peripheral blood monocytes (PBMO)], both in terms of phagocytosis and killing of Escherichia coli. We investigated whether CBMO are less sensitive toward PICD compared with PBMO. Monocytes were infected with green fluorescent protein (GFP)-labeled E. coli. Phagocytic activity, cell-count, Annexin V staining, hypoploid DNA content, CD95 and CD95L expression, and caspase-8 and -9 activities were analyzed by flow cytometry, ROS production by chemiluminescence, and CD95L mRNA expression by reverse-transcriptase polymerase chain reaction. With equal phagocytic activity and ROS production, PBMO cell count was decreased by 82 +/- 6% versus 28 +/- 8% for CBMO after infection. Annexin V binding was enhanced fivefold on PBMO; 56 +/- 15% of PBMO showed a hypodiploid DNA content compared with 9 +/- 6% of CBMO. Caspases CD95L and CD95L mRNA were up-regulated in PBMO. Our results indicate that CBMO are less sensitive toward E. coli-mediated PICD than PBMO. Modifying monocyte apoptosis may be a target for future interventions in sepsis.

Kurzfassung Das produzierende Gewerbe in Deutschland ist auf Grund starker internationaler Konkurrenz, ständig zunehmender Qualitäts- und Leistungsanforderungen sowie einer steigenden Variantenvielfalt zur permanenten Weiterentwicklung der Wertschöpfungsprozesse gezwungen. Das Forschungsprojekt IDproBlech befasst sich vor diesem Hintergrund mit der Entwicklung, Implementierung und Steuerung innovativer Leistungsbündel aus physischen Produkten und produktionsnahen Dienstleistungen in der Prozesskette Blechverarbeitung. Übergeordnetes Ziel ist die optimierte Allokation vorhandener und neuer Leistungen innerhalb der Prozesskette. Durch eine umfassende Identifikation und Analyse bereits vorhandener Dienstleistungen, die Gestaltung neuer Dienstleistungen sowie durch die anschließende Entwicklung von Leistungsbündeln und Geschäftsmodellen sollen neue Marktpotenziale erschlossen werden. Die Vorgehensweise umfasst für die Leistungsbündel entwickelte technische Lösungen sowie ein Konzept zur erweiterten Bewertung der Wirtschaftlichkeit von Geschäftsmodellen.

Blood monocyte-derived macrophages invading the alveolus encounter pulmonary surfactant, a phospholipoprotein complex that changes composition during lung development. We tested the hypothesis that characteristic phosphatidylcholine (PC) components differentially influence macrophage phenotype and function, as determined by phagocytosis of green fluorescent protein-labeled Escherichia coli and alphaCD3-induced T cell proliferation. Human macrophages were exposed to surfactant (Curosurf(R)), to two of its characteristic phosphadidylcholine (PC) components (dipalmitoyl-PC and palmitoylmyristoyl-PC), and to a ubiquituous PC (palmitoyloleoyl-PC) as control. Interaction of Curosurf and PC species with macrophages was assessed using Lissaminetrade mark-dihexadecanoyl-phosphoethanolamine-labeled liposomes. Curosurf and both saturated surfactant PC species downregulated CD14 expression and upregulated CD206. HLA-DR and CD80 were upregulated by Curosurf and palmitoylmyristoyl-PC, whereas dipalmitoyl-PC showed no effect. The latter upregulated TLR2 and TLR4 expression, whereas Curosurf and palmitoylmyristoyl-PC had no effect. PC species tested were incorporated in comparable amounts by macrophages. Curosurf and PC species inhibited phagocytosis of E. coli. Scavenger receptor CD36, CD68, SR-A, and LOX-1 mRNA expression was upregulated by Curosurf, whereas PC species only upregulated SR-A. Curosurf and palmitoylmyristoyl-PC inhibited alphaCD3-induced T cell proliferation by 50%, whereas dipalmitoyl-PC and palmitoyloleoyl-PC showed no effect. These data identify individual surfactant PC species as modifiers of macrophage differentiation and suggest differential effects on innate and adaptive immune functions.

Bacterial infection remains the main cause of neonatal morbidity and mortality. With clinical signs unspecific and little, its course is fulminant, and only early antibiotic therapy protects from d

Tolerance induction toward the semiallogeneic fetus is crucial to enable a successful pregnancy; its failure is associated with abortion or preterm delivery. Skewing T cell differentiation toward a Th2-dominated phenotype seems to be pivotal in maternal immune adaption, yet underlying mechanisms are incompletely understood. Myeloid-derived suppressor cells (MDSCs) are innate immune cells that mediate T cell suppression and are increased in cord blood of healthy newborns and in peripheral blood of pregnant women. In this study, we demonstrate that granulocytic MDSCs (GR-MDSCs) accumulate in human placenta of healthy pregnancies but are diminished in patients with spontaneous abortions. Placental GR-MDSCs effectively suppressed T cell responses by expression of arginase I and production of reactive oxygen species and were activated at the maternal–fetal interface through interaction with trophoblast cells. Furthermore, GR-MDSCs isolated from placenta polarized CD4+ T cells toward a Th2 cytokine response. These results highlight a potential role of GR-MDSCs in inducing and maintaining maternal–fetal tolerance and suggest them as a promising target for therapeutic manipulation of pregnancy complications.

The expanding genus Bartonella includes zoonotic and human-specific pathogens that can cause a wide range of clinical manifestations. A productive infection allowing bacterial transmission by blood-sucking arthropods is marked by an intraerythrocytic bacteremia that occurs exclusively in specific human or animal reservoir hosts. Incidental human infection by animal-adapted bartonellae can cause disease without evidence for erythrocyte parasitism. A better understanding of the intraerythrocytic lifestyle of bartonellae may permit the design of strategies to control the reservoir and transmittable stages of these emerging pathogens. We have dissected the process of Bartonella erythrocyte parasitism in experimentally infected animals using a novel approach for tracking blood infections based on flow cytometric quantification of green fluorescent protein–expressing bacteria during their interaction with in vivo–biotinylated erythrocytes. Bacteremia onset occurs several days after inoculation by a synchronous wave of bacterial invasion into mature erythrocytes. Intracellular bacteria replicate until reaching a stagnant number, which is sustained for the remaining life span of the infected erythrocyte. The initial wave of erythrocyte infection is followed by reinfection waves occurring at intervals of several days. Our findings unravel a unique bacterial persistence strategy adapted to a nonhemolytic intracellular colonization of erythrocytes that preserves the pathogen for efficient transmission by blood-sucking arthropods.