Phagocytosis induced cell death (PICD) is crucial for controlling phagocyte effector cells, such as monocytes, at sites of infection, and essentially contributes to termination of inflammation. Here ...we tested the hypothesis, that during PICD bystander apoptosis of non-phagocyting monocytes occurs, that apoptosis induction is mediated via tumor necrosis factor-alpha (TNF-α and that TNF-α secretion and -signalling is causal. Monocytes were infected with Escherichia coli (E. coli), expressing green fluorescent protein (GFP), or a pH-sensitive Eos-fluorescent protein (EOS-FP). Monocyte phenotype, phagocytic activity, apoptosis, TNF-receptor (TNFR)-1, -2-expression and TNF-α production were analyzed. Apoptosis occured in phagocyting and non-phagocyting, bystander monocytes. Bacterial transport to the phagolysosome was no prerequisite for apoptosis induction, and desensitized monocytes from PICD, as confirmed by EOS-FP expressing E. coli. Co-cultivation with non-infected carboxyfluorescein-succinimidyl-ester- (CFSE-) labelled monocytes resulted in significant apoptotic cell death of non-infected bystander monocytes. This process required protein de-novo synthesis and still occurred in a diminished way in the absence of cell-cell contact. E. coli induced a robust TNF-α production, leading to TNF-mediated apoptosis in monocytes. Neutralization with an anti-TNF-α antibody reduced monocyte bystander apoptosis significantly. In contrast to TNFR2, the pro-apoptotic TNFR1 was down-regulated on the monocyte surface, internalized 30 min. p.i. and led to apoptosis predominantly in monocytes without phagocyting bacteria by themselves. Our results suggest, that apoptosis of bystander monocytes occurs after infection with E. coli via internalization of TNFR1, and indicate a relevant role for TNF-α. Modifying monocyte apoptosis in sepsis may be a future therapeutic option.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
Data from 14,926 preterm infants with birth weight <1500 g and gestational age between 22 0/7 weeks and 31 6/7 collected between January 2009 and December 2017 were analyzed for frequency of early-onset sepsis (EOS) and late-onset sepsis (LOS) and for causative pathogens. Risk factors for the development of EOS and LOS and outcomes after EOS and LOS were analyzed by multivariate logistic regression models.
EOS occurred in 1.1% of infants and LOS in 11.9%. Escherichia coli was the most common pathogen in EOS, coagulase-negative staphylococci in LOS. Multidrug-resistant organisms were detected in 8.4% of EOS and 3.9% of LOS cases. Risk factors for EOS were lower gestational age, intra-amniotic infection and spontaneous delivery. Risk factors for LOS were lower gestational age, small for gestational age, central lines, endotracheal ventilation and history of EOS. Both EOS and LOS were independently associated with adverse neonatal outcome.
These data from a large German neonatal cohort confirm neonatal sepsis as the most common cause of morbidity and mortality in VLBW infants, as well as E. coli and coagulase-negative staphylococci as the most prevalent pathogens. Multidisciplinary approaches such as antibiotic stewardship, hygiene and feeding strategies are necessary to further reduce the burden of sepsis in VLBW infants.
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 pO
physiologically is low but rises immediately after birth.
In this study, the effect of low oxygen partial pressure (pO
) 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.
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.
Taken together, our results show a diminished activation of cord blood immune cells by low pO
, which might contribute to impaired reactivity in the context of infection.
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.
The newborn's immune system is faced with the challenge of having to learn quickly to fight off infectious agents, but tolerating the colonization of the body surfaces with commensals without ...reacting with an excessive inflammatory response. Myeloid‐derived suppressor cells (MDSC) are innate immune cells with suppressive activity on other immune cells that regulate fetal‐maternal tolerance during pregnancy and control intestinal inflammation in neonates. Until now, nothing is known about the role of MDSC in microbiome establishment. One of the transcription factors regulating MDSC homeostasis is the hypoxia‐inducible factor 1α (HIF‐1α). We investigated the impact of HIF‐1α on MDSC accumulation and microbiome establishment during the neonatal period in a mouse model with targeted deletion of HIF‐1α in myeloid cells (Hif1a loxP/loxPLysMCre+). We show that in contrast to wildtype mice, where an extensive expansion of MDSC was observed, MDSC expansion in neonatal Hif1a loxP/loxPLysMCre+ mice was dramatically reduced both systemically and locally in the intestine. This was accompanied by an altered microbiome composition and intestinal T‐cell homeostasis. Our results point toward a role of MDSC in inflammation regulation in the context of microbiome establishment and thus reveal a new aspect of the biological role of MDSC during the neonatal period.
The first article reporting that injections of synthetic non‐replicating mRNA could be used for vaccination, originated from a French team and was published in the European Journal of Immunology in 1993. Research performed before and after in several countries has contributed to the development of the efficient modern mRNA vaccines.
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 A
receptors on monocytes.
Adenosine acts by inducing MDSCs and upregulating inhibitory A
receptors, probably as a mode of autoregulation. Thus, adenosine contributes to immunosuppressive status and may be a target for immunomodulation during pre- and postnatal development.
Immune 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
receptor on monocytes. Adenosine upregulates expression of IDO in MDSCs and monocytes potentially contributing to their suppressive activity.
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.
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.
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.
Our results suggest that probiotics increase the defence functions of neonatal monocytes and thus possibly favourably influence the newborn's ability to fight infections.
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.
Bacterial re‐programming of PBMC‐derived monocytes induces the emergence of a distinct monocytic phenotype with profound phagocytic impairments but a preserved ability for naïve T cell stimulation.
...Septic diseases are characterized by an initial systemic, proinflammatory phase, followed by a period of anti‐inflammation. In the context of the latter, monocytes have been described to display altered functions, including reduced TNF secretion and T cell‐stimulating capacities in response to recall antigens. This hyporesponsiveness is supposed to be detrimental for coping with secondary infections. We here characterize bacterially reprogrammed PBMC‐derived monocytes with special focus on their phagocytic activity. Hence, we have implemented a surrogate model of the early, postinflammatory period by exposing PBMCs to Escherichia coli on d0 and rechallenging them with bacteria on d2. This induced the emergence of a distinct monocytic phenotype with profound phagocytic impairments but a preserved ability for naïve T cell stimulation. The compromising effects on phagocytosis required the presence of bacteria and were not mimicked by TLR4 ligation or exposure to isolated cytokines alone. Moreover, the impairments were specific for the engulfment of bacteria and were coupled to a selective down‐regulation of FcγR and SR expression. Intriguingly, this monocytic phenotype contributed to the stimulation of a TH17‐polarized adaptive immune response in the context of secondary infection. Our findings extend the current knowledge of monocytic reprogramming and identify the phagocytic capacity of monocytes as a putative sepsis biomarker.
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.
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.
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).
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.
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.
Newborns and especially preterm infants are much more susceptible to infections than adults. The pathogens causing infections in newborns are often detectable in the intestinal flora of affected ...children even before disease onset. Therefore, it seems reasonable to prevent dysbiosis in newborns and preterm infants. An approach followed in many neonatal intensive care units (NICUs) is to prevent infections in preterm infants with probiotics however their mechanisms of action of probiotics are incompletely understood. Here, we investigated the effect of perinatal probiotic exposure on immune cells in newborn mice.
Pregnant mice were orally treated with a combination of Lactobacillus acidophilus and Bifidobacterium bifidum (Infloran®) from mid-pregnancy until the offspring were harvested. Immune cell composition in organs of the offspring were analyzed by flow cytometry.
Perinatal probiotic exposure had profound effects on immune cell composition in the intestine, liver and lungs of newborn mice with reduction of myeloid and B cells and induction of T cells in the probiotic treated animals' organs at weaning. Furthermore, probiotic exposure had an effect on T cell development in the thymus.
Our results contribute to a better understanding of the interaction of probiotics with the developing immune system.
probiotics have profound effects on immune cell composition in intestines, livers and lungs of newborn mice. probiotics modulate T cell development in thymus of newborn mice. effects of probiotics on neonatal immune cells are particularly relevant in transition phases of the microbiome. our results contribute to a better understanding of the mechanisms of action of probiotics in newborns.
PDF
