Fetal lung growth predicts the risk for early-life respiratory infections and childhood asthma.

BACKGROUND: Early-life respiratory infections and asthma are major health burdens during childhood. Markers predicting an increased risk for early-life respiratory diseases are sparse. Here, we identified the predictive value of ultrasound-monitored fetal lung growth for the risk of early-life respiratory infections and asthma. METHODS: Fetal lung size was serially assessed at standardized time points by transabdominal ultrasound in pregnant women participating in a pregnancy cohort. Correlations between fetal lung growth and respiratory infections in infancy or early-onset asthma at five years were examined. Machine-learning models relying on extreme gradient boosting regressor or classifier algorithms were developed to predict respiratory infection or asthma risk based on fetal lung growth. For model development and validation, study participants were randomly divided into a training and a testing group, respectively, by the employed algorithm. RESULTS: Enhanced fetal lung growth throughout pregnancy predicted a lower early-life respiratory infection risk. Male sex was associated with a higher risk for respiratory infections in infancy. Fetal lung growth could also predict the risk of asthma at five years of age. We designed three machine-learning models to predict the risk and number of infections in infancy as well as the risk of early-onset asthma. The models' R2 values were 0.92, 0.90 and 0.93, respectively, underscoring a high accuracy and agreement between the actual and predicted values. Influential variables included known risk factors and novel predictors, such as ultrasound-monitored fetal lung growth. CONCLUSION: Sonographic monitoring of fetal lung growth allows to predict the risk for early-life respiratory infections and asthma.

Towards decoding the space-time continuum of pregnancy.

Pregnancy is likely nature's most elaborate model of dynamic adaptations occurring over a distinct period of time at specific sites of the maternal body. Spatially-resolved transcriptomic analyses now enable the comprehensive decoding of these dynamic adaptations during the early onset stages of mammalian pregnancies and throughout fetal development.

Increased late preterm birth risk and altered uterine blood flow upon exposure to heat stress.

BACKGROUND: Climate change, in particular the exposure to heat, impacts on human health and can trigger diseases. Pregnant people are considered a vulnerable group given the physiological changes during pregnancy and the potentially long-lasting consequences for the offspring. Evidence published to date on higher risk of pregnancy complications upon heat stress exposure are from geographical areas with high ambient temperatures. Studies from geographic regions with temperate climates are sparse; however, these areas are critical since individuals may be less equipped to adapt to heat stress. This study addresses a significant gap in knowledge due to the temperature increase documented globally. METHODS: Birth data of singleton pregnancies (n = 42,905) from a tertiary care centre in Hamburg, Germany, between 1999 and 2021 were retrospectively obtained and matched with climate data from the warmer season (March to September) provided by the adjacent federal meteorological station of the German National Meteorological Service to calculate the relative risk of heat-associated preterm birth. Heat events were defined by ascending temperature percentiles in combination with humidity over exposure periods of up to 5 days. Further, ultrasound data documented in a longitudinal prospective pregnancy cohort study (n = 612) since 2012 were used to identify pathophysiological causes of heat-induced preterm birth. FINDINGS: Both extreme heat and prolonged periods of heat exposure increased the relative risk of preterm birth (RR: 1.59; 95% CI: 1.01-2.43; p = 0.045; RR: 1.20; 95% CI: 1.02-1.40; p = 0.025). We identified a critical period of heat exposure during gestational ages 34-37 weeks that resulted in increased risk of late preterm birth (RR: 1.67; 95% CI: 1.14-1.43; p = 0.009). Pregnancies with a female fetus were more prone to heat stress-associated preterm birth. We found heat exposure was associated with altered vascular resistance within the uterine artery. INTERPRETATION: Heat stress caused by high ambient temperatures increases the risk of preterm birth in a geographical region with temperate climate. Prenatal routine care should be revised in such regions to provide active surveillance for women at risk. FUNDING: Found in acknowledgements.

Climate change and pregnancy complications: From hormones to the immune response.

Pregnant women are highly vulnerable to adverse environments. Accumulating evidence highlights that increasing temperatures associated with the ongoing climate change pose a threat to successful reproduction. Heat stress caused by an increased ambient temperature can result in adverse pregnancy outcomes, e.g., preterm birth, stillbirth and low fetal weight. The pathomechanisms through which heat stress interferes with pregnancy maintenance still remain vague, but emerging evidence underscores that the endocrine system is severely affected. It is well known that the endocrine system pivotally contributes to the physiological progression of pregnancy. We review - sometimes speculate - how heat stress can offset hormonal dysregulations and subsequently derail other systems which interact with hormones, such as the immune response. This may account for the heat-stress related threat to successful pregnancy progression, fetal development and long-term children's health.

Anti-SARS-CoV-2 antibodies in breast milk during lactation after infection or vaccination: A cohort study.

Breast milk is a pivotal source to provide passive immunity in newborns over the first few months of life. Very little is known about the antibody transfer levels over the period of breastfeeding. We conducted a prospective study in which we evaluated concentrations of anti-SARS-CoV-2 Spike IgA and RBD IgG/M/A antibodies in maternal serum and breast milk over a duration of up to 6 months after delivery. We compared antibody levels in women with confirmed COVID-19 infection during pregnancy (n = 16) to women with prenatal SARS-CoV-2 vaccination (n = 5). Among the recovered women, n = 7 (44%) had been vaccinated during the lactation period as well. We observed intraindividual moderate positive correlations between antibody levels in maternal serum and breast milk (r = 0.73, p-value<0.0001), whereupon the median levels were generally higher in serum. Anti-RBD IgA/M/G transfer into breast milk was significantly higher in women recovered from COVID-19 and vaccinated during lactation (35.15 AU/ml; IQR 21.96-66.89 AU/ml) compared to the nonvaccinated recovered group (1.26 AU/ml; IQR 0.49-3.81 AU/ml), as well as in the vaccinated only group (4.52 AU/ml; IQR 3.19-6.23 AU/ml). Notably, the antibody level in breast milk post SARS-CoV-2 infection sharply increased following a single dose of vaccine. Breast milk antibodies in all groups showed neutralization capacities against an early pandemic SARS-CoV-2 isolate (HH-1) and moreover, also against the Omicron variant, although with lower antibody titer. Our findings highlight the importance of booster vaccinations especially after SARS-CoV-2 infection in pregnancy in order to optimize protection in mother and newborn.

Tissue-resident immunity in the female and male reproductive tract.

The conception of how the immune system is organized has been significantly challenged over the last years. It became evident that not all lymphocytes are mobile and recirculate through secondary lymphoid organs. Instead, subsets of immune cells continuously reside in tissues until being reactivated, e.g., by a recurring pathogen or other stimuli. Consequently, the concept of tissue-resident immunity has emerged, and substantial evidence is now available to support its pivotal function in maintaining tissue homeostasis, sensing challenges and providing antimicrobial protection. Surprisingly, insights on tissue-resident immunity in the barrier tissues of the female reproductive tract are sparse and only slowly emerging. The need for protection from vaginal and amniotic infections, the uniqueness of periodic tissue shedding and renewal of the endometrial barrier tissue, and the demand for a tailored decidual immune adaptation during pregnancy highlight that tissue-resident immunity may play a crucial role in distinct compartments of the female reproductive tract. This review accentuates the characteristics of tissue-resident immune cells in the vagina, endometrium, and the decidua during pregnancy and discusses their functional role in modulating the risk for infertility, pregnancy complications, infections, or cancer. We here also review data published to date on tissue-resident immunity in the male reproductive organs, which is still a largely uncharted territory.

Infant immunity against viral infections is advanced by the placenta-dependent vertical transfer of maternal antibodies.

Neonatal passive immunity, derived from transplacental transfer of IgG antibodies from mother to fetus during pregnancy, can mitigate the risk for severe infections in the early postnatal period. Understanding the placenta as the gateway organ in this process, we aimed to evaluate the influence of specific factors modulating the transplacental IgG transfer rate (TPTR) in 141 mother/neonate pairs. We further evaluated the potential health advantage elicited by maternal IgG with regard to respiratory tract infections during infancy and early childhood. Data and biological samples collected within the prospective longitudinal pregnancy cohort study PRINCE (Prenatal Identification of Children's Health) were used for these analyses. We tested IgG antibody levels against seven pathogens (measles, mumps, rubella, tetanus, diphtheria, pertussis and influenza A) by ELISA and detected seropositivity in 72.6-100% of pregnant women and in 76.3-100% of their neonates, respectively. Cord blood IgG levels reached 137-160% of levels detected in maternal blood. Strikingly, assessment of TPTR for all seven antigens highlighted that TPTR strongly depends on individual placental function. Subsequent in-depth analysis of anti-influenza A IgG revealed a link between cord blood levels and uterine perfusion, measured by uterine artery pulsatility index. Moreover, higher cord blood anti-influenza A IgG levels were associated with a significantly reduced risk for respiratory tract infections during the first six months of life, indicating a high degree of cross-reactivity and possible pathogen-agnostic effects of anti-influenza A antibodies. Taken together, our data suggest that early life immunity is modulated by maternal IgG levels and individual placental features such as perfusion. Vaccination of pregnant women, i.e. against influenza, can increase neonatal antibody levels and hereby protect against early life respiratory infections. Consequently, specific guidelines should evolve in order to safeguard neonates born from pregnancies with poorer placental capacity for vertical transfer of protective antibodies.

Disruption of Glucocorticoid Action on CD11c+ Dendritic Cells Favors the Generation of CD4+ Regulatory T Cells and Improves Fetal Development in Mice.

A wealth of innate and adaptive immune cells and hormones are involved in mounting tolerance towards the fetus, a key aspect of successful reproduction. We could recently show that the specific cross talk between the pregnancy hormone progesterone and dendritic cells (DCs) is significantly engaged in the generation of CD4+ FoxP3+ regulatory T (Treg) cells while a disruption led to placental alterations and intra-uterine growth restriction. Apart from progesterone, also glucocorticoids affect immune cell functions. However, their functional relevance in the context of pregnancy still needs clarification. We developed a mouse line with a selective knockout of the glucocorticoid receptor (GR) on DCs, utilizing the cre/flox system. Reproductive outcome and maternal immune and endocrine adaptation of Balb/c-mated C57Bl/6 GRflox/floxCD11ccre/wt (mutant) females was assessed on gestation days (gd) 13.5 and 18.5. Balb/c-mated C57Bl/6 GRwt/wtCD11ccre/wt (wt) females served as controls. The number of implantation and fetal loss rate did not differ between groups. However, we identified a significant increase in fetal weight in fetuses from mutant dams. While the frequencies of CD11c+ cells remained largely similar, a decreased expression of co-stimulatory molecules was observed on DCs of mutant females on gd 13.5, along with higher frequencies of CD4+ and CD8+ Treg cells. Histomorphological and gene expression analysis revealed an increased placental volume and an improved functional placental capacity in mice lacking the GR on CD11c+ DCs. In summary, we here demonstrate that the disrupted communication between GCs and DCs favors a tolerant immune microenvironment and improves placental function and fetal development.

Vertically transferred maternal immune cells promote neonatal immunity against early life infections.

During mammalian pregnancy, immune cells are vertically transferred from mother to fetus. The functional role of these maternal microchimeric cells (MMc) in the offspring is mostly unknown. Here we show a mouse model in which MMc numbers are either normal or low, which enables functional assessment of MMc. We report a functional role of MMc in promoting fetal immune development. MMc induces preferential differentiation of hematopoietic stem cells in fetal bone marrow towards monocytes within the myeloid compartment. Neonatal mice with higher numbers of MMc and monocytes show enhanced resilience against cytomegalovirus infection. Similarly, higher numbers of MMc in human cord blood are linked to a lower number of respiratory infections during the first year of life. Our data highlight the importance of MMc in promoting fetal immune development, potentially averting the threats caused by early life exposure to pathogens.

Inefficient Placental Virus Replication and Absence of Neonatal Cell-Specific Immunity Upon Sars-CoV-2 Infection During Pregnancy.

Pregnant women have been carefully observed during the COVID-19 pandemic, as the pregnancy-specific immune adaptation is known to increase the risk for infections. Recent evidence indicates that even though most pregnant have a mild or asymptomatic course, a severe course of COVID-19 and a higher risk of progression to diseases have also been described, along with a heightened risk for pregnancy complications. Yet, vertical transmission of the virus is rare and the possibility of placental SARS-CoV-2 infection as a prerequisite for vertical transmission requires further studies. We here assessed the severity of COVID-19 and onset of neonatal infections in an observational study of women infected with SARS-CoV-2 during pregnancy. Our placental analyses showed a paucity of SARS-CoV-2 viral expression ex vivo in term placentae under acute infection. No viral placental expression was detectable in convalescent pregnant women. Inoculation of placental explants generated from placentas of non-infected women at birth with SARS-CoV-2 in vitro revealed inefficient SARS-CoV-2 replication in different types of placental tissues, which provides a rationale for the low ex vivo viral expression. We further detected specific SARS-CoV-2 T cell responses in pregnant women within a few days upon infection, which was undetectable in cord blood. Our present findings confirm that vertical transmission of SARS-CoV-2 is rare, likely due to the inefficient virus replication in placental tissues. Despite the predominantly benign course of infection in most mothers and negligible risk of vertical transmission, continuous vigilance on the consequences of COVID-19 during pregnancy is required, since the maternal immune activation in response to the SARS-CoV2 infection may have long-term consequences for children's health.

Pathogenesis of preterm birth: bidirectional inflammation in mother and fetus.

Preterm birth (PTB) complicates 5-18% of pregnancies globally and is a leading cause of maternal and fetal morbidity and mortality. Most PTB is spontaneous and idiopathic, with largely undefined causes. To increase understanding of PTB, much research in recent years has focused on using animal models to recapitulate the pathophysiology of PTB. Dysfunctions of maternal immune adaptations have been implicated in a range of pregnancy pathologies, including PTB. A wealth of evidence arising from mouse models as well as human studies is now available to support that PTB results from a breakdown in fetal-maternal tolerance, along with excessive, premature inflammation. In this review, we examine the current knowledge of the bidirectional communication between fetal and maternal systems and its role in the immunopathogenesis of PTB. These recent insights significantly advance our understanding of the pathogenesis of PTB, which is essential to ultimately designing more effective strategies for early prediction and subsequent prevention of PTB.

In-depth characterization of monocyte subsets during the course of healthy pregnancy.

Pregnancy represents an immunological challenge for the maternal immune system. Pregnancy augments innate immune responses, and particularly monocytes contribute to maintaining the balance between pro- and anti-inflammatory immune responses required for the successful sequence of distinct immunological phases throughout pregnancy. Nonetheless, studies that focus on the heterogeneity of monocytes and analyze the alteration of monocyte subsets in a longitudinal approach throughout healthy pregnancies have remained scarce. In this study, we characterized the gradual phenotypic changes of monocyte subsets and the secretory potential of bulk monocytes in peripheral blood mononuclear cells of healthy pregnant women from a population-based prospective birth cohort study. Blood samples at predefined time points were analyzed using flow cytometry for in-depth characterization of monocyte subsets, which confirmed a shift from classical towards intermediate monocytes throughout pregnancy. Principal component analysis revealed characteristic phenotypic changes on monocyte subsets, especially on the intermediate monocyte subset, throughout pregnancy. Pregnancy-related hormones were measured in serum and ß-human chorionic gonadotropin levels were significantly associated with expression of CD11b, CD116 and CCR2 on monocyte subsets. TLR4 and TLR7/8 stimulation of monocytes furthermore showed reduced polycytokine production towards the end of pregnancy. These data provide a comprehensive overview of phenotypic changes and secretory potential of monocytes in healthy pregnant women and establish a selective contribution of different monocyte subsets to healthy pregnancy. The results from this study therefore build a basis for future comparisons and evaluation of women with adverse pregnancy outcomes.

Vertically Transferred Immunity in Neonates: Mothers, Mechanisms and Mediators.

Over the last years, an increasing number of outbreaks of vaccine-preventable infectious diseases has been reported. Besides elderly and immunocompromised individuals, newborns and small infants are most susceptible to infections, as their immune system is still immature. This vulnerability during infancy can be mitigated by the transplacental transfer of pathogen-specific antibodies and other mediators of immunity from mother to the fetus during pregnancy, followed postnatally by breast milk-derived immunity. Since this largely antibody-mediated passive immunity can prevent the newborn from infections, neonatal immunity depends strongly on the maternal concentration of respective specific antibodies during pregnancy. If titers are low or wane rapidly after birth, the protection transferred to the child may not be sufficient to prevent disease. Moreover, emerging concepts propose that mothers may transfer active immunity to the newborns via vertical transfer of pathogen-specific T cells. Overall, a promising strategy to augment and prolong neonatal immunity is to vaccinate the mother before or during pregnancy in order to boost maternal antibody concentrations or availability of specific T cells. Hence, a large number of pre-and postconceptional vaccine trials have been carried out to test and confirm this concept. We here highlight novel insights arising from recent research endeavors on the influence of prenatal maternal vaccination against pathogens that can pose a threat for newborns, such as measles, pertussis, rubella and influenza A. We delineate pathways involved in the transfer of specific maternal antibodies. We also discuss the consequences for children's health and long-term immunity resulting from an adjustment of prenatal vaccination regimes.

The mnemonic code of pregnancy: Comparative analyses of pregnancy success and complication risk in first and second human pregnancies.

Obstetrical complications such as spontaneous abortion/miscarriage, fetal growth restriction, preeclampsia or preterm birth occur in approx. 15% of human pregnancies. Clinical experts often state that a previous uncomplicated pregnancy reduces the risk for complications in subsequent pregnancies. Vice versa, a prior pregnancy affected by obstetrical complications increases the risk for reoccurrence. However, published evidence directly underpinning these clinical statements is sparse. Considering that the maternal immune adaptation may be causally involved in determining the outcome of subsequent pregnancies, a comprehensive analysis of clinical data was long overdue. We here present a systematic analysis of clinical data using a PubMed-based approach to identify human studies with relevant information on birth weight and incidences of pregnancy complications in first and second pregnancies. From initially 18,592 publications, 37 studies were included in the quantitative data analysis. Women with a previous pregnancy affected by complications where a derailed immune response can be inferred have a 2.2-3.2-fold increased risk to be affected again in a subsequent pregnancy. Conversely, a normally progressing primary pregnancy reduced the risk for complications in a subsequent pregnancy by 35-65%. Moreover, an uncomplicated primary pregnancy was associated with a 4.2% increased birth weight in a following pregnancy without a difference in gestational age at delivery. In conclusion, the increased birth weight after previously uncomplicated pregnancies suggests that an immune memory is mounted during primary pregnancies. This immune memory may promote the successful outcome of subsequent pregnancies or - if missing or compromised - account for a risk perpetuation of pregnancy complications.

When 3 Rs meet a forth R: Replacement, reduction and refinement of animals in research on reproduction.

Research endeavors aiming to understand the maternal immune adaptation to pregnancy significantly rely on the use of animal models, such as mice and rats. These models have provided important insights into the pathophysiology of a number of pregnancy disorders in humans. However, the use of animal models in scientific research is a vividly debated and emotive topic. The 3R principles - replacement, reduction and refinement of research animals - have been propagated a few decades ago. The present review advocates a forward-thinking consciousness to address the 3R principles in research projects in the field of reproductive biology and immunology. Specific measures and alternative methods are being proposed to replace research animals by using e.g. tissue engineering approaches, biobank-derived tissue, 'placenta-on-a-chip' devices or in silico methods. The latter may involve data queries from repositories now available to provide single cell sequencing information on reproductive tissues. Reduction of research animals by gestational imaging and a wealth of suggestions for refinement are proposed. Taken together, the measures and guidelines introduced in this review are expected to spark a reconsideration of experimental designs in the area of reproductive biology and immunology in order to implement 3R principle where applicable.

Impaired Progesterone-Responsiveness of CD11c+ Dendritic Cells Affects the Generation of CD4+ Regulatory T Cells and Is Associated With Intrauterine Growth Restriction in Mice.

Up to 10% of pregnancies in Western societies are affected by intrauterine growth restriction (IUGR). IUGR reduces short-term neonatal survival and impairs long-term health of the children. To date, the molecular mechanisms involved in the pathogenesis of IUGR are largely unknown, but the failure to mount an adequate endocrine and immune response during pregnancy has been proposed to facilitate the occurrence of IUGR. A cross talk between the pregnancy hormone progesterone and innate immune cell subsets such as dendritic cells (DCs) is vital to ensure adequate placentation and fetal growth. However, experimental strategies to pinpoint distinct immune cell subsets interacting with progesterone in vivo have long been limited. In the present study, we have overcome this limitation by generating a mouse line with a specific deletion of the progesterone receptor (PR) on CD11c+ DCs. We took advantage of the cre/loxP system and assessed reproductive outcome in Balb/c-mated C57Bl/6 PRflox/floxCD11ccre/wt females. Balb/c-mated C57Bl/6 PRwt/wtCD11ccre/wt females served as controls. In all dams, fetal growth and development, placental function and maternal immune and endocrine adaptation were evaluated at different gestational time points. We observed a significantly reduced fetal weight on gestational day 13.5 and 18.5 in PRflox/floxCD11ccre/wt females. While frequencies of uterine CD11c+ cells were similar in both groups, an increased frequency of co-stimulatory molecules was observed on DCs in PRflox/floxCD11ccre/wt mice, along with reduced frequencies of CD4+ FoxP3+ and CD8+ CD122+ regulatory T (Treg) cells. Placental histomorphology revealed a skew toward increased junctional zone at the expense of the labyrinth in implantations of PRflox/floxCD11ccre/wt females, accompanied by increased plasma progesterone concentrations. Our results support that DCs are highly responsive to progesterone, subsequently adapting to a tolerogenic phenotype. If such cross talk between progesterone and DCs is impaired, the generation of pregnancy-protective immune cells subsets such as CD4+ and CD8+ Treg cells is reduced, which is associated with poor placentation and IUGR in mice.

Progesterone modulates the T-cell response via glucocorticoid receptor-dependent pathways.

PROBLEM: Steroid hormones such as progesterone and glucocorticoids rise during pregnancy and are accountable for the adaptation of the maternal immune system to pregnancy. How steroid hormones induce fetal tolerance is not fully understood. We hypothesized that steroid hormones selectively regulate the T-cell response by promoting T-cell death. METHOD OF STUDY: We incubated murine spleen cells isolated from non-pregnant and pregnant mice with physiological concentrations of steroid hormones in vitro and analyzed T-cell subsets after 48 h of incubation. Results We found that progesterone and the synthetic glucocorticoid dexamethasone induce T-cell death. CD4+ regulatory T (Treg ) cells were refractory toward progesterone-induced cell death, in contrast to conventional CD4+ T cells, which resulted in a preferential enrichment of CD4+ Treg cells in culture. T cells isolated from pregnant mice at early and late gestation showed comparable sensitivity to steroid-induced cell death. The target receptor for progesterone in immune cells is controversially discussed. We provide here support of progesterone binding to the glucocorticoid receptor as only T cells lacking the glucocorticoid but not the progesterone receptor showed resistance against progesterone-induced death. Conclusions Our results indicate that high levels of progesterone during pregnancy can induce selective T-cell death by binding the glucocorticoid receptor. Although physiological hormone concentrations were used, due to different bioavailability of steroid hormones in vivo these results have to be validated in an in vivo model. This mechanism might ensure immunological tolerance at the feto-maternal interface at gestation.

Developmental origin and sex-specific risk for infections and immune diseases later in life.

The intrauterine environment is an important determinant of immunity later in life of the offspring. An altered prenatal immune development can result in a high postnatal risk for infections, chronic immune diseases, and autoimmunity. Many of these immune diseases show a strong sex bias, such as a high incidence of autoimmune diseases and allergies in adult females or a high risk for infections in males. Here, we comprehensively review established pathways and propose novel concepts modulating the risk for such poor immunity during childhood and throughout life. Moreover, we highlight how an adverse fetal environment may affect or aggravate the risk for poor immunity in a sex-specific manner. An improved understanding of a sex-specific susceptibility to poor immunity along with insights on how such risk can be modulated before or around birth will allow the development of tailored prevention strategies.