Fetal microchimerism and maternal health: a review and evolutionary analysis of cooperation and conflict beyond the womb

Maternal-driven immune education in offspring

Maternal environmental exposures, particularly during gestation and lactation, significantly influence the immunological development and long-term immunity of offspring. Mammalian immune systems develop through crucial inputs from the environment, beginning in utero and continuing after birth. These critical developmental windows are essential for proper immune system development and, once closed, may not be reopened. This review focuses on the mechanisms by which maternal exposures, particularly to pathogens, diet, and microbiota, impact offspring immunity. Mechanisms driving maternal-offspring immune crosstalk include transfer of maternal antibodies, changes in the maternal microbiome and microbiota-derived metabolites, and transfer of immune cells and cytokines via the placenta and breastfeeding. We further discuss the role of transient maternal infections, which are common during pregnancy, in providing tissue-specific immune education to offspring. We propose a "maternal-driven immune education" hypothesis, which suggests that offspring can use maternal encounters that occur during a critical developmental window to develop optimal immune fitness against infection and inflammation.

Are fetal microchimerism and circulating fetal extracellular vesicles important links between spontaneous preterm delivery and maternal cardiovascular disease risk?

Trafficking and persistence of fetal microchimeric cells (fMCs) and circulating extracellular vesicles (EVs) have been observed in animals and humans, but their consequences in the maternal body and their mechanistic contributions to maternal physiology and pathophysiology are not yet fully defined. Fetal cells and EVs may help remodel maternal organs after pregnancy-associated changes, but the cell types and EV cargos reaching the mother in preterm pregnancies after exposure to various risk factors can be distinct from term pregnancies. As preterm delivery-associated maternal complications are rising, revisiting this topic and formulating scientific questions for future research to reduce the risk of maternal morbidities are timely. Epidemiological studies report maternal cardiovascular risk as one of the major complications after preterm delivery. This paper suggests a potential link between fMCs and circulating EVs and adverse maternal cardiovascular outcomes post-pregnancies, the underlying mechanisms, consequences, and methods for and how this link might be assessed.

The 'communicatome' of pregnancy: spotlight on cellular and extravesicular chimerism

Communication via biological mediators between mother and fetus are key to reproductive success and offspring's future health. The repertoire of mediators coding signals between mother and fetus is broad and includes soluble factors, membrane-bound particles and immune as well as non-immune cells. Based on the emergence of technological advancements over the last years, considerable progress has been made toward deciphering the "communicatome" between fetus and mother during pregnancy and even after birth. In this context, pregnancy-associated chimerism has sparked the attention among immunologists, since chimeric cells-although low in number-are maintained in the allogeneic host (mother or fetus) for years after birth. Other non-cellular structures of chimerism, e.g. extracellular vesicles (EVs), are increasingly recognized as modulators of pregnancy outcome and offspring's health. We here discuss the origin, distribution and function of pregnancy-acquired microchimerism and chimeric EVs in mother and offspring. We also highlight the pioneering concept of maternal microchimeric cell-derived EVs in offspring. Such insights expand the understanding of pregnancy-associated health or disease risks in mother and offspring.

Maternal gut microbiota in the health of mothers and offspring: from the perspective of immunology

Due to the physiological alteration during pregnancy, maternal gut microbiota changes following the metabolic processes. Recent studies have revealed that maternal gut microbiota is closely associated with the immune microenvironment in utero during pregnancy and plays a vital role in specific pregnancy complications, including preeclampsia, gestational diabetes, preterm birth and recurrent miscarriages. Some other evidence has also shown that aberrant maternal gut microbiota increases the risk of various diseases in the offspring, such as allergic and neurodevelopmental disorders, through the immune alignment between mother and fetus and the possible intrauterine microbiota. Probiotics and the high-fiber diet are effective inventions to prevent mothers and fetuses from diseases. In this review, we summarize the role of maternal gut microbiota in the development of pregnancy complications and the health condition of future generations from the perspective of immunology, which may provide new therapeutic strategies for the health management of mothers and offspring.

Sperm intrusion into the implantation-stage blastocyst and its potential biological significance

The human embryo derives from fusion of oocyte and sperm, undergoes growth and differentiation, resulting in a blastocyst. To initiate implantation, the blastocyst hatches from the zona pellucida, allowing access from external inputs. Modelling of uterine sperm distribution indicates that 200-5000 sperm cells may reach the implantation-stage blastocyst following natural coitus. We show ultrastructural evidence of sperm cells intruding into trophectoderm cells of zona-free blastocysts obtained from the uterus of rhesus monkeys. Interaction between additional sperm and zona-free blastocyst could be an evolutionary feature yielding adaptive processes influencing the developmental fate of embryos. This process bears potential implications in pregnancy success, sperm competition and human health.

Pregnancy and superior moral status: a proposal for two thresholds of personhood

In this paper, I suggest that, if we are committed to accepting a threshold approach to personhood, according to which all beings above the threshold are persons with equal moral status, there are strong reasons to also recognise a second threshold that would be reached through human pregnancy, and that would confer on pregnant women a temporary superior moral status. This proposal is not based on the moral status of the fetus, but on the moral status of the pregnant woman. It is not only the fetus which is an organism sui generis: the pregnant woman, also, is a unique being. Following almost any view on the moral status of the fetus, the pregnant woman should be regarded, herself, as more than a singular individual. She is, herself, 'more than one'. Pregnant women are also necessary for the continued survival of the human species, and there are important justice-based reasons to recognise the higher status. Furthermore, the recognition of a superior moral status for pregnant women does not imply that pregnancy should always be viewed as desirable, or imply any position on the permissibility of abortion. My proposal is not as radical as it might seem, as it does not require that pregnant women should always receive superior treatment, but only that they should to some extent. It could have a range of potential positive practical consequences. Finally, my approach does not threaten, but rather promotes, human equality.

Sex dimorphism and cancer immunotherapy: May pregnancy solve the puzzle?

In the immunoncology era, growing evidence has shown a clear sex dimorphism in antitumor immune response with a potential impact on outcomes upon immunecheckpoint blockade (ICI) in patients with cancer. Sex dimorphism could affect tumor microenvironment composition and systemic anticancer immunity; however, the modifications induced by sex are heterogeneous. From a clinical perspective, six metanalyses have explored the role of sex in cancer patients receiving ICI with conflicting results. Environmental and reproductive factors may further jeopardize the sex-related heterogeneity in anticancer immune response. In particular, pregnancy is characterized by orchestrated changes in the immune system, some of which could be long lasting. A persistence of memory T-cells with a potential fetal-antigen specificity has been reported both in human and mice, suggesting that a previous pregnancy may positively impact cancer development or response to ICI, in case of fetal-antigen sharing from tumor cells. On the other hand, a previous pregnancy may also be associated with a regulatory memory characterized by increased tolerance and anergy towards cancer-fetal common antigens. Finally, fetal-maternal microchimerism could represent an additional source of chronic exposure to fetal antigens and may have important immunological implications on cancer development and ICI activity. So far, the role of pregnancy dimorphism (nulliparous vs parous) in women and the impact of pregnancy-related variables remain largely underexplored in cancer patients. In this review, we summarize the evidence regarding sex and pregnancy dimorphism in the context of immune response and anticancer immunotherapy and advocate the importance of analyzing pregnancy variables on ICIs clinical trials.

Adaptation in the face of internal conflict: the paradox of the organism revisited

The paradox of the organism refers to the observation that organisms appear to function as coherent purposeful entities, despite the potential for within-organismal components like selfish genetic elements and cancer cells to erode them from within. While it is commonly accepted that organisms may pursue fitness maximisation and can be thought to hold particular agendas, there is a growing recognition that genes and cells do so as well. This can lead to evolutionary conflicts between an organism and the parts that reside within it. Here, we revisit the paradox of the organism. We first outline its conception and relationship to debates about adaptation in evolutionary biology. Second, we review the ways selfish elements may exploit organisms, and the extent to which this threatens organismal integrity. To this end, we introduce a novel classification scheme that distinguishes between selfish elements that seek to distort transmission versus those that seek to distort phenotypic traits. Our classification scheme also highlights how some selfish elements elude a multi-level selection decomposition using the Price equation. Third, we discuss how the organism can retain its status as the primary fitness-maximising agent in the face of selfish elements. The success of selfish elements is often constrained by their strategy and further limited by a combination of fitness alignment and enforcement mechanisms controlled by the organism. Finally, we argue for the need for quantitative measures of both internal conflicts and organismality.

Poor glucose control and markers of placental dysfunction correlate with increased circulating fetal microchimerism in diabetic pregnancies

Fetal microchimerism (FMc) arises during pregnancy as fetal cells enter maternal circulation and remain decades postpartum. Circulating FMc is increased in preeclampsia, fetal growth restriction, and as we recently showed, is associated with biomarkers of placental dysfunction in normotensive term pregnancies. Diabetes mellitus (DM) also correlates with placental dysfunction. We hypothesize that poor glucose control and markers of placental dysfunction are associated with increased circulating FMc in diabetic pregnancies. We included 122 pregnancies preceding active labor (pregestational DM, n = 77, gestational DM (GDM), n = 45) between 2001 and 2017. Maternal and fetal samples were genotyped for various human leukocyte antigen (HLA) loci, and other polymorphisms to identify fetus-specific alleles. We used validated polymerase chain reaction (PCR) assays to quantify FMc in maternal peripheral blood buffy coat. Negative binomial regression with adjustment for confounders was used to assess FMc quantity. In pregestational DM, increased circulating FMc correlated with elevation of HbA1c (≥ 6.0 %) (detection rate ratio (DRR) = 4.9, p = 0.010) and a 1000 pg/mL rise in the anti-angiogenic biomarker soluble fms-like tyrosine kinase-1 (sFlt-1) (DRR = 1.1, p = 0.011). In GDM, increased FMc correlated with elevated 2-hour oral glucose tolerance test results (DRR = 2.3, p = 0.046) and birthweight < 10th or > 90th percentile (DRR = 4.2, p = 0.049). These findings support our novel hypothesis that FMc correlates with poor glucose control and various aspects of placental dysfunction in DM. Whether increased FMc in pregnancies with poor glucose control and placental dysfunction contributes to the risk of preeclampsia in diabetic pregnancies and to the increased risk of chronic cardiovascular disease later in life remains to be investigated.

Fetal microchimerism and the two-stage model of preeclampsia

Fetal cells cross the placenta during pregnancy and some have the ability to persist in maternal organs and circulation long-term, a phenomenon termed fetal microchimerism. These cells often belong to stem cell or immune cell lineages. The long-term effects of fetal microchimerism are likely mixed, potentially depending on the amount of fetal cells transferred, fetal-maternal histocompatibility and fetal cell-specific properties. Both human and animal data indicate that fetal-origin cells partake in tissue repair and may benefit maternal health overall. On the other hand, these cells have been implicated in inflammatory diseases by studies showing increased fetal microchimerism in women with autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. During pregnancy, preeclampsia is associated with increased cell-transfer between the mother and fetus, and an increase in immune cell subsets. In the current review, we discuss potential mechanisms of transplacental transfer, including passive leakage across the compromised diffusion barrier and active recruitment of cells residing in the placenta or fetal circulation. Within the conceptual framework of the two-stage model of preeclampsia, where syncytiotrophoblast stress is a common pathophysiological pathway to maternal and fetal clinical features of preeclampsia, we argue that microchimerism may represent a mechanistic link between stage 1 placental dysfunction and stage 2 maternal cardiovascular inflammation and endothelial dysfunction. Finally, we postulate that fetal microchimerism may contribute to the known association between placental syndromes and increased long-term maternal cardiovascular disease risk. Fetal microchimerism research represents an exciting opportunity for developing new disease biomarkers and targeted prophylaxis against maternal diseases.

Microchimerism as a source of information on future pregnancies

Small numbers of fetal cells cross the placenta during pregnancy turning mothers into microchimeras. Fetal cells from all previous pregnancies accumulate forming the mother's fetal microchiome. What is significant about microchimeric cells is that they have been linked to health problems including reproductive and autoimmune diseases. Three decades after the discovery of fetal microchimerism, the function of these cells remains a mystery. Here, we contend that the role of microchimeric cells is to inform the fetus about the likelihood that its genes are present in future pregnancies. We argue that, when genes are more likely than average to be in future maternal siblings, fetuses will send a fixed number of cells that will not elicit a maternal immune response against them. However, when genes are less likely to be in future maternal siblings, fetuses will send an ever-increasing number of cells that will elicit an ever-stronger maternal immune response. Our work can explain the observed clinical association between microchimeric cells and pre-eclampsia. However, our work predicts that this association should be stronger in women with a genetically diverse microchiome. If supported by medical tests, our work would allow establishing the likelihood of pregnancy or autoimmune problems advising medical interventions.

Quantification of Female Chimeric Cells in the Tonsils of Male Children and Their Determinants

The factors influencing mother-to-child cell trafficking and persistence over children's lives have yet to be established. The quantification of maternal microchimerism was previously reported through HLA-based approaches, which introduced bias regarding the tolerogenic environment. We aimed to identify cells of maternal origin irrespective of the HLA repertoire and to ascertain the determinants of microchimeric cells. This case-control study enrolled 40 male infants attending pediatric surgery from January 2022 to October 2022. Female cells were quantified in infants' tonsil tissue by using cytogenetic fluorescent in situ hybridization (FISH) coupled with optimized automated microscopy. Out of the 40 infants, half (47.4%) had been breastfed for more than one month, a quarter for less a month, and 10 children (26.3%) were never breastfed. XX cells were observed in male tonsils in two-thirds of participants at a median density of 5 cells per 100,000 cells. In univariate analyses, child age was negatively associated with a high female cell density. In exploratory multivariate analyses, previous breastfeeding is a likely determinant of the persistence of these cells in the host, as well as the rank among siblings. Part of the benefit of breastmilk for child health may therefore be driven by breastfeeding-related microchimerism.

Y-chromosome in the olfactory neuroepithelium as a potential biomarker of depression in women with male offspring: an exploratory study

The persistence of fetal cells in the mother (fetal microchimerism (FMc)) has been described in maternal tissues essential to the newborn. FMc is associated with several diseases that start or worsen in pregnancy or postpartum. This exploratory study reports-for the first time-the presence of FMc in the olfactory neuroepithelium (ON) of both healthy and depressed women with male offspring. However, depressed women had fewer microchimeric cells (digital PCR). The existence of FMc in the ON could facilitate mother-child bonding. These findings open new pathways to study FMc in the ON, female depression, and mother-child bonding.

Is chimerism associated with cancer across the tree of life?

Chimerism is a widespread phenomenon across the tree of life. It is defined as a multicellular organism composed of cells from other genetically distinct entities. This ability to 'tolerate' non-self cells may be linked to susceptibility to diseases like cancer. Here we test whether chimerism is associated with cancers across obligately multicellular organisms in the tree of life. We classified 12 obligately multicellular taxa from lowest to highest chimerism levels based on the existing literature on the presence of chimerism in these species. We then tested for associations of chimerism with tumour invasiveness, neoplasia (benign or malignant) prevalence and malignancy prevalence in 11 terrestrial mammalian species. We found that taxa with higher levels of chimerism have higher tumour invasiveness, though there was no association between malignancy or neoplasia and chimerism among mammals. This suggests that there may be an important biological relationship between chimerism and susceptibility to tissue invasion by cancerous cells. Studying chimerism might help us identify mechanisms underlying invasive cancers and also could provide insights into the detection and management of emerging transmissible cancers.

Microchimerism as Post-Transplant Marker of a Chronic Rejection Process

The risk of losing a transplanted organ is high, and non-invasive markers to warn of this phenomenon are still being sought. We investigated the impact of post-transplant microchimerism on the function of the transplanted kidney. The study included 100 kidney transplant recipients, mostly women. All transplanted organs were from opposite-sex deceased donors. Microchimerism was assessed using multiplex PCR. Male DNA was detected in all urine samples from female recipients and in 13/56 blood samples from female kidney recipients. Female DNA was found in 31/44 urine samples from male recipients, but in none of the blood samples. Microchimerism in the urine of female recipients correlated positively with blood urea (Rs = 0.45; p = 5.84 × 10^-4) and K⁺ ions (Rs = 0.29; p = 0.03), while microchimerism in the blood of female recipients also correlated positively with blood urea (Rs = 0. 28; p = 0.04), cystatin C (Rs = 0.31; p = 0.02) and the number of incompatible HLA alleles (Rs = 0.42; p = 0.01). A history of DGF was associated with higher urinary donor DNA concentrations in female recipients.: Post-transplant microchimerism may serve as a potential marker of chronic kidney rejection.

Role of Inflammaging on the Reproductive Function and Pregnancy

During female lifetime and pregnancy, inflammation and cellular senescence are implicated in physiological processes, from ovulation and menstruation, to placental homeostasis and delivery. Several lifestyles, nutritional, and environmental insults, as well as long-lasting pregestational inflammatory diseases may lead to detrimental effects in promoting and sustaining a chronic excessive inflammatory response and inflammaging, which finally contribute to the decay of fertility and pregnancy outcome, with a negative effect on placental function, fetal development, and future health risk profile in the offspring. Maladaptation to pregnancy and obstetric disease may in turn increase maternal inflammaging in a feedback loop, speeding up aging processes and outbreak of chronic diseases. Maternal inflammaging may also impact, through transgenerational effects, on future adult health. Hence, efficacious interventions should be implemented by physicians and healthcare professionals involved in prevention activities to reduce the modifiable factors contributing to the inflammaging process in order to improve public health.

Microchimerism in multiple sclerosis: The association between sex of offspring and MRI features in women with multiple sclerosis

Aims

During pregnancy, fetal cells can migrate to the mother via blood circulation. A percentage of these cells survive in maternal tissues for decades generating a population of fetal microchimeric cells (fMCs), whose biological role is unclear. The aim of this study was to investigate the association between the sex of offspring, an indirect marker of fMCs, and magnetic resonance imaging (MRI) features in women with multiple sclerosis (MS).

Methods

We recruited 26 nulliparous MS patients (NPp), 20 patients with at least one male son (XYp), and 8 patients with only daughters (XXp). Each patient underwent brain MR scan to acquire 3D-T2w FLAIR FatSat and 3D-T1w FSPGR/TFE. Lesion Segmentation Tool (LST) and FreeSurfer were used to obtain quantitative data from MRI. Additional data were collected using medical records. Multiple regression models were applied to evaluate the association between sex of offspring and MS data.

Results

Comparing NPp and XXp, we found that NPp had larger 4th ventricle volume (2.02 ± 0.59 vs. 1.70 ± 0.41; p = 0.022), smaller left entorhinal volume (0.55 ± 0.17 vs. 0.68 ± 0.25; p = 0.028), and lower thickness in the following cortical areas: left paracentral (2.34 ± 0.16 vs. 2.39 ± 0.17; p = 0.043), left precuneus (2.27 ± 0.11 vs. 2.34 ± 0.16; p = 0.046), right lateral occipital (2.14 ± 0.11 vs. 2.25 ± 0.08; p = 0.006). NPp also had lower thickness in left paracentral cortex (2.34 ± 0.16 vs. 2.46 ± 0.17; p = 0.004), left precalcarine cortex (1.64 ± 0.14 vs. 1.72 ± 0.12; p = 0.041), and right paracentral cortex (2.34 ± 0.17 vs. 2.42 ± 0.14; p = 0.015) when compared to XYp. Comparing XYp and XXp, we found that XYp had higher thickness in left cuneus (1.80 ± 0.14 vs. 1.93 ± 0.10; p = 0.042) and left pericalcarine areas (1.59 ± 0.19 vs. 1.72 ± 0.12; p = 0.032) and lower thickness in right lateral occipital cortex (2.25 ± 0.08 vs. 2.18 ± 0.13; p = 0.027).

Discussion

Our findings suggested an association between the sex of offspring and brain atrophy. Considering the sex of offspring as an indirect marker of fMCs, we speculated that fMCs could accumulate in different brain areas modulating MS neuropathological processes.

Age-restricted functional and developmental differences of neonatal platelets

BACKGROUND

Developmental ontogeny of neonatal thrombopoiesis retains characteristics that are distinct from adults although molecular mechanisms remain unestablished.

METHODS

We applied multiparameter quantitative platelet responses with integrated ribosome profiling/transcriptomic studies to better define gene/pathway perturbations regulating the neonatal-to-adult transition. A bioinformatics pipeline was developed to identify stable, neonatal-restricted platelet biomarkers for clinical application.

RESULTS

Cord blood (CB) platelets retained the capacity for linear agonist-receptor coupling linked to phosphatidylserine (PS) exposure and α-granule release, although a restricted block in cross-agonist activation pathways was evident. Functional immaturity of synergistic signaling pathways was due to younger ontogenetic age and singular underdevelopment of the protein secretory gene network, with reciprocal expansion of developmental pathways (E2F, G2M checkpoint, c-Myc) important for megakaryocytopoiesis. Genetic perturbations regulating vesicle transport and fusion (TOM1L1, VAMP3, SNAP23, and DNM1L) and PS exposure and procoagulant activity (CLCN3) were the most significant, providing a molecular explanation for globally attenuated responses. Integrated transcriptomic and ribosomal footprints identified highly abundant (ribosome-protected) DEFA3 (encoding human defensin neutrophil peptide 3) and HBG1 as stable biomarkers of neonatal thrombopoiesis. Studies comparing CB- or adult-derived megakaryocytopoiesis confirmed inducible and abundant DEFA3 antigenic expression in CB megakaryocytes, ~3.5-fold greater than in leukocytes (the most abundant source in humans). An initial feasibility cohort of at-risk pregnancies manifested by maternal/fetal hemorrhage (chimerism) were applied for detection and validation of platelet HBG1 and DEFA3 as neonatal thrombopoiesis markers, most consistent for HBG1, which displayed gestational age-dependent expression.

CONCLUSIONS

These studies establish an ontogenetically divergent stage of neonatal thrombopoiesis, and provide initial feasibility studies to track disordered fetal-to-adult megakaryocytopoiesis in vivo.

Synergies of Extracellular Vesicles and Microchimerism in Promoting Immunotolerance During Pregnancy

The concept of biological identity has been traditionally a central issue in immunology. The assumption that entities foreign to a specific organism should be rejected by its immune system, while self-entities do not trigger an immune response is challenged by the expanded immunotolerance observed in pregnancy. To explain this "immunological paradox", as it was first called by Sir Peter Medawar, several mechanisms have been described in the last decades. Among them, the intentional transfer and retention of small amounts of cells between a mother and her child have gained back attention. These microchimeric cells contribute to expanding allotolerance in both organisms and enhancing genetic fitness, but they could also provoke aberrant alloimmune activation. Understanding the mechanisms used by microchimeric cells to exert their function in pregnancy has proven to be challenging as per definition they are extremely rare. Profiting from studies in the field of transplantation and cancer research, a synergistic effect of microchimerism and cellular communication based on the secretion of extracellular vesicles (EVs) has begun to be unveiled. EVs are already known to play a pivotal role in feto-maternal tolerance by transferring cargo from fetal to maternal immune cells to reshape their function. A further aspect of EVs is their function in antigen presentation either directly or on the surface of recipient cells. Here, we review the current understanding of microchimerism in the feto-maternal tolerance during human pregnancy and the potential role of EVs in mediating the allorecognition and tropism of microchimeric cells.

Ontogeny of the Dyad: the Relationship Between Maternal and Offspring Neuroendocrine Function

PURPOSE OF REVIEW

We review ontogeny of the maternal-offspring neuroendocrine relationship in human pregnancy. We present bidirectional genetic, physiological, and behavioral influences that enhance or disrupt HPA activity and its end product cortisol at the individual level and within the dyad.

RECENT FINDINGS

Consistent evidence supports that maternal mood and caregiving behavior are associated with maternal and offspring cortisol levels. Select studies support the buffering effects of antidepressant use and maternal positive affect on offspring cortisol. Growing research highlights evocative effects of fetal neuroendocrine activity, antenatal gene transfer, and infant behavioral distress and risk characteristics on maternal cortisol levels and dyadic attunement. There is potential to advance our understanding of the mother-offspring neuroendocrine relationship by consideration of other neuroactive steroids in addition to cortisol, and to consider developmental timing and measurement source in study design. Future study should emphasize in what context or for whom neuroendocrine attunement is adaptive versus maladaptive for mother and child.

Preimplantation chromosomal mosaics, chimaeras and confined placental mosaicism

Some human preimplantation embryos are chromosomally mosaic. For technical reasons, estimates of the overall frequency vary widely from <15 to >90% and the true frequency remains unknown. Aneuploid/diploid and aneuploid/aneuploid mosaics typically arise during early cleavage stages before the embryonic genome is fully activated and when cell cycle checkpoints are not operating normally. Other mosaics include chaotic aneuploid mosaics and mixoploids, some of which arise by abnormal chromosome segregation at the first cleavage division. Chimaeras are similar to mosaics, in having two genetically distinct cell populations, but they arise from more than one zygote and occur less often. After implantation, the frequency of mosaic embryos declines to about 2% and most are trisomic/diploid mosaics, with trisomic cells confined to the placenta. Thus, few babies are born with chromosomal mosaicism. This review discusses the origin of different types of chromosomal mosaics and chimaeras; their fate and the relationship between preimplantation chromosomal mosaicism and confined placental mosaicism in human conceptuses and animal models. Abnormal cells in mosaic embryos may be depleted by cell death, other types of cell selection or cell correction but the most severely affected mosaic embryos probably die. Trisomic cells could become restricted to placental lineages if cell selection or correction is less effective in placental lineages and/or they are preferentially allocated to a placental lineage. However, the relationship between preimplantation mosaicism and confined placental mosaicism may be complex because the specific chromosome(s) involved will influence whether chromosomally abnormal cells survive predominately in the placental trophoblast and/or placental mesenchyme.

Lay summary

Human cells normally have 23 pairs of chromosomes, which carry the genes. During the first few days of development, some human embryos are chromosomal mosaics. These mosaic embryos have both normal cells and cells with an abnormal number of chromosomes, which arise from the same fertilised egg. (More rarely, the different cell populations arise from more than one fertilised egg and these embryos are called chimaeras.) If chromosomally abnormal cells survive to term, they could cause birth defects. However, few abnormal cells survive and those that do are usually confined to the placenta, where they are less likely to cause harm. It is not yet understood how this restriction occurs but the type of chromosomal abnormality influences which placental tissues are affected. This review discusses the origin of different types of chromosomally abnormal cells, their fate and how they might become confined to the placenta in humans and animal models.

Immune cell type and DNA methylation vary with reproductive status in women: possible pathways for costs of reproduction

Background

Consistent with evolutionarily theorized costs of reproduction (CoR), reproductive history in women is associated with life expectancy and susceptibility to certain cancers, autoimmune disorders and metabolic disease. Immunological changes originating during reproduction may help explain some of these relationships.

Methodology

To explore the potential role of the immune system in female CoR, we characterized leukocyte composition and regulatory processes using DNA methylation (DNAm) in a cross-sectional cohort of young (20–22 years old) women differing in reproductive status.

Results

Compared to nulliparity, pregnancy was characterized by differential methylation at 828 sites, 96% of which were hypomethylated and enriched for genes associated with T-cell activation, innate immunity, pre-eclampsia and neoplasia. Breastfeeding was associated with differential methylation at 1107 sites (71% hypermethylated), enriched for genes involved in metabolism, immune self-recognition and neurogenesis. There were no significant differences in DNAm between nulliparous and parous women. However, compared to nullipara, pregnant women had lower proportions of B, CD4T, CD8T and natural killer (NK) cells, and higher proportions of granulocytes and monocytes. Monocyte counts were lower and NK counts higher among breastfeeding women, and remained so among parous women.

Implications

Our findings point to widespread differences in DNAm during pregnancy and lactation. These effects appear largely transient, but may accumulate with gravidity become detectable as women age. Nulliparous and parous women differed in leukocyte composition, consistent with more persistent effects of reproduction on cell type. These findings support transient (leukocyte DNAm) and persistent (cell composition) changes associated with reproduction in women, illuminating potential pathways contributing to CoR.

Lay Summary: Evolutionary theory and epidemiology support costs of reproduction (CoR) to women’s health that may involve changes in immune function. We report differences in immune cell composition and gene regulation during pregnancy and breastfeeding. While many of these differences appear transient, immune cell composition may remain, suggesting mechanisms for female CoR.

The behavioural and physiological ecology of embryos: responding to the challenges of life inside an egg

Adaptations of post-hatching animals have attracted far more study than have embryonic responses to environmental challenges, but recent research suggests that we have underestimated the complexity and flexibility of embryos. We advocate a dynamic view of embryos as organisms capable of responding - on both ecological and evolutionary timescales - to their developmental environments. By viewing embryos in this way, rather than assuming an inability of pre-hatching stages to adapt and respond, we can broaden the ontogenetic breadth of evolutionary and ecological research. Both biotic and abiotic factors affect embryogenesis, and embryos exhibit a broad range of behavioural and physiological responses that enable them to deal with changes in their developmental environments in the course of interactions with their parents, with other embryos, with predators, and with the physical environment. Such plasticity may profoundly affect offspring phenotypes and fitness, and in turn influence the temporal and spatial dynamics of populations and communities. Future research in this field could benefit from an integrated framework that combines multiple approaches (field investigations, manipulative experiments, ecological modelling) to clarify the mechanisms and consequences of embryonic adaptations and plasticity.

Feto-maternal microchimerism: Memories from pregnancy

There is a bidirectional transplacental cell trafficking between mother and fetus during pregnancy in placental mammals. The presence and persistence of fetal cells in maternal tissues are known as fetal microchimerism (FMc). FMc has high multilineage potential with a great ability to differentiate and functionally integrate into maternal tissue. FMc has been found in various maternal tissues in animal models and humans. Its permanence in the maternal body up to decades after delivery suggests it might play an essential role in maternal pathophysiology. Studying the presence, localization, and characteristics of FMc in maternal tissues is key to understanding its impact on the woman's body. Here we comprehensively review the existence of FMc in different species and organs and tissues, aiming to better characterize their possible role in human health and disease. We also highlight several methodological considerations that would optimize the detection, quantification, and functional determination of FMc.

Reinterpreting patterns of variation in human thyroid function: An evolutionary ecology perspective

Thyroid hormone reference intervals—used to determine normal thyroid function —currently don’t take into account many significant factors that can cause variation in thyroid hormone levels. These factors include age, sex, ethnicity, season, time of day, iodine content in the diet, socioeconomic status, stress levels, body composition, immune status, menstrual cycle phase, and overall health status. This paper shows how early life experiences as well as short term stressors may affect variation in thyroid function. These are energetic challenges to which the thyroid physiology can respond to. Our investigation shows that much variation in thyroid function is natural. It may result from a complex interplay of evolutionary, genetic, developmental, and physiological factors in response to energetic challenges in the environment, beyond what is currently considered in biomedicine. A new research agenda for thyroid health should explore the way that diversity in thyroid function has evolved as a response to different contexts people live in—like focusing on how people’s metabolisms adapt to the energetic requirements of their environments.

Two hundred million people worldwide experience some form of thyroid disorder, with women being especially at risk. However, why human thyroid function varies between populations, individuals, and across the lifespan has attracted little research to date. This limits our ability to evaluate the conditions under which patterns of variation in thyroid function are best understood as ‘normal’ or ‘pathological’. In this review, we aim to spark interest in research aimed at understanding the causes of variation in thyroid phenotypes. We start by assessing the biomedical literature on thyroid imbalance to discuss the validity of existing reference intervals for diagnosis and treatment across individuals and populations. We then propose an evolutionary ecological framework for understanding the phylogenetic, genetic, ecological, developmental, and physiological causes of normal variation in thyroid function. We build on this approach to suggest testable predictions for how environmental challenges interact with individual circumstances to influence the onset of thyroid disorders. We propose that dietary changes, ecological disruptions of co-evolutionary processes during pregnancy and with pathogens, emerging infections, and exacerbated stress responses can contribute to explaining the onset of thyroid diseases. For patients to receive the best personalized care, research into the causes of thyroid variation at multiple levels is needed.

Amniotic fluid stem cells and the cell source repertoire for non-invasive prenatal testing

Cell-free fetal DNA (cffDNA)-based non-invasive prenatal testing (NIPT) is considered to be a very promising screening tool for pregnant women with an increased risk of fetal aneuploidy. Already millions of women worldwide underwent NIPT. However, due to the observed false-positive and false-negative results, this screening approach does not fulfil the criteria of a diagnostic test. Accordingly, positive results still require risk-carrying invasive prenatal testing, such as amniocentesis or chorionic villus sampling (CVS), for confirmation. Such hurdles need to be overcome before NIPT could become a diagnostic approach widely used in the general population. Here we discuss new evidence that besides the placenta amniotic fluid stem cells (AFSCs) could also represent an origin of cffDNA in the mother’s blood. A comprehensive picture of the involved cell source repertoire could pave the way to more reliable interpretations of NIPT results and ameliorate counselling of advice-seeking patients.

The maternal gut microbiome during pregnancy and offspring allergy and asthma

Environmental exposures during pregnancy that alter both the maternal gut microbiome and the infant's risk of allergic disease and asthma include a traditional farm environment and consumption of unpasteurized cow's milk, antibiotic use, dietary fiber and psychosocial stress. Multiple mechanisms acting in concert may underpin these associations and prime the infant to acquire immune competence and homeostasis following exposure to the extrauterine environment. Cellular and metabolic products of the maternal gut microbiome can promote the expression of microbial pattern recognition receptors, as well as thymic and bone marrow hematopoiesis relevant to regulatory immunity. At birth, transmission of maternally derived bacteria likely leverages this in utero programming to accelerate postnatal transition from a Th2 to Th1 and Th17 dominant immune phenotypes and maturation of regulatory immune mechanisms, which in turn reduce the child's risk of allergic disease and asthma. Although our understanding of these phenomena is rapidly evolving, the field is relatively nascent, and we are yet to translate existing knowledge into interventions that substantially reduce disease risk in humans. Here we review evidence that the maternal gut microbiome impacts the offspring's risk of allergic disease and asthma, discuss challenges and future directions for the field, and propose the hypothesis that maternal carriage of Prevotella copri during pregnancy decreases the offspring's risk of allergic disease via production of succinate which in turn promotes bone marrow myelopoiesis of dendritic cell precursors in the fetus.

Fetomaternal microchimerism and genetic diagnosis: On the origins of fetal cells and cell-free fetal DNA in the pregnant woman

During pregnancy several types of fetal cells and fetal stem cells, including pregnancy-associated progenitor cells (PAPCs), traffic into the maternal circulation. Whereas they also migrate to various maternal organs and adopt the phenotype of the target tissues to contribute to regenerative processes, fetal cells also play a role in the pathogenesis of maternal diseases. In addition, cell-free fetal DNA (cffDNA) is detectable in the plasma of pregnant women. Together they constitute the well-known phenomenon of fetomaternal microchimerism, which inspired the concept of non-invasive prenatal testing (NIPT) using maternal blood. An in-depth knowledge concerning the origins of these fetal cells and cffDNA allows a more comprehensive understanding of the biological relevance of fetomaternal microchimerism and has implications for the ongoing expansion of resultant clinical applications.

Heat Shock Proteins: Potential Modulators and Candidate Biomarkers of Peripartum Cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening condition in which heart failure and systolic dysfunction occur late in pregnancy or within months following delivery. To date, no reliable biomarkers or therapeutic interventions for the condition exist, thus necessitating an urgent need for identification of novel PPCM drug targets and candidate biomarkers. Leads for novel treatments and biomarkers are therefore being investigated worldwide. Pregnancy is generally accompanied by dramatic hemodynamic changes, including a reduced afterload and a 50% increase in cardiac output. These increased cardiac stresses during pregnancy potentially impair protein folding processes within the cardiac tissue. The accumulation of misfolded proteins results in increased toxicity and cardiac insults that trigger heart failure. Under stress conditions, molecular chaperones such as heat shock proteins (Hsps) play crucial roles in maintaining cellular proteostasis. Here, we critically assess the potential role of Hsps in PPCM. We further predict specific associations between the Hsp types Hsp70, Hsp90 and small Hsps with several proteins implicated in PPCM pathophysiology. Furthermore, we explore the possibility of select Hsps as novel candidate PPCM biomarkers and drug targets. A better understanding of how these Hsps modulate PPCM pathogenesis holds promise in improving treatment, prognosis and management of the condition, and possibly other forms of acute heart failure.

Validation of fetal microchimerism after pregnancy in the ovine using qPCR

Fetal microchimerism has been detected in maternal tissues of humans and rodents during and after pregnancy. Studies focusing on fetal DNA transfer to maternal tissues in domestic animals are limited, especially in sheep. Fetal ram DNA was observed in the maternal circulation during pregnancy, but it is not known if this chimerism persists in soft tissues after parturition. The objectives of this exploratory study were to: 1) determine if male fetal DNA is detectable in soft tissues of mature ewes after parturition and if so, determine if detection repeatability differed with lifetime offspring sex ratio and 2) determine if male fetal DNA was present in soft tissues of yearling (primiparous) ewes shortly after parturition. Eight mature (open, non-lactating) and 8 yearling (primiparous, periparturient) Rambouillet ewes were used. Mature ewes (5- to 7-yr old) had given birth to primarily 82% males (n = 4) or 71% female (n = 4) over a lifetime. Yearling ewes had birthed either a singleton male (n = 4) or female (n = 4) lambs. DNA was extracted from 10 and 11 different soft tissues from the mature and yearling ewes, respectively. Real-time PCR (qPCR) was used to identify the presence of the SRY gene in each tissue sample. Male DNA was detected in the brain and liver from one mature open ewe that had given birth to two males and six females during her lifetime. In younger ewes that gave birth to a ram lamb, male DNA was observed in the thyroid of one ewe and the pancreas and brain of a second ewe. Male DNA was detected in the ovary of one ewe that had given birth to a female lamb. Based on these data, we suggest fetal microchimerism in soft maternal tissues is possible in sheep and may remain after pregnancy has ended. The detection repeatability of male fetal DNA was not associated with sex ratio of lifetime offspring. Male DNA was observed in maternal soft tissues collected shortly after parturition. The greater detection of fetal male DNA found in younger ewes shortly after parturition may be due to not having enough time for fetal DNA clearance to occur. Future studies are warranted to further study XY chimerism in maternal tissues of the ewe and its potential role in ovine physiology.

Inflammaging: Blame the sons. Relationships between the number of sons and the level of inflammatory mediators among post-reproductive women

OBJECTIVES

Reproduction is costly, but sons and daughters differently influence maternal physiology, also in older age. In particular, having sons may negatively influence maternal health and may be associated with a shorter life span of mothers. Sons may also contribute to increased inflammaging, a chronic sub-clinical systemic inflammatory state characterized by elevated levels of serum inflammatory mediators. The aim of this study was to examine the impact of the total number of children, and the number of daughters and sons separately on concentrations of C-reactive protein (CRP), and proinflammatory cytokines such as interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α).

MATERIALS AND METHODS

The participants were 378 women aged 45-92 who had 3.9 (SD 2.12, median = 4, range = 0-13) children, including 2.1 (SD 1.46, median = 2, range = 0-8) sons and 1.8 (SD 1.44, median = 2, range = 0-7) daughters on average.

RESULTS

We found a positive relationship between the overall number of children and IL-6 levels. CRP and IL-6 concentrations were positively associated with the number of sons but not with the number of daughters. Each son increased maternal CRP level by 11%, and IL-6 level by 6%. Neither the total number of children nor the number of daughters or sons were related to the TNF-α concentration.

DISCUSSION

Aging-associated inflammation in post-reproductive mothers with a higher number of sons supports the hypothesis of trade-offs between reproduction and health. Furthermore, these results provide new evidence contributing to the idea that having sons may have more detrimental effects on the maternal organism than having daughters.

Out of balance: the role of evolutionary mismatches in the sex disparity in autoimmune disease

Over the past century autoimmune disease incidence has increased rapidly in (post-) industrialised, affluent societies, suggesting that changes in ecology and lifestyle are driving this development. Epidemiological studies show that (i) 80% of autoimmune disease patients are female, (ii) autoimmune diseases co-occur more often in women, and (iii) the incidence of some autoimmune diseases is increasing faster in women than in men. The female preponderance in autoimmunity is most pronounced between puberty and menopause, suggesting that diverging sex hormone levels during the reproductive years are implicated in autoimmune disease development. Using an evolutionary perspective, we build on the hypotheses that female immunity is cyclical in menstruating species and that natural selection shaped the female immune system to optimise the implantation and gestation of a semi-allogeneic foetus. We propose that cyclical immunomodulation and female immune tolerance mechanisms are currently out of balance because of a mismatch between the conditions under which they evolved and (post-)industrialised, affluent lifestyles. We suggest that current changes in autoimmune disease prevalence may be caused by increases in lifetime exposure to cyclical immunomodulation and ovarian hormone exposure, reduced immune challenges, increased reproductive lifespan, changed reproductive patterns, and enhanced positive energy balance associated with (post-)industrialised, affluent lifestyles. We discuss proximate mechanisms by which oestrogen and progesterone influence tolerance induction and immunomodulation, and review the effect of the menstrual cycle, pregnancy, and contraceptive use on autoimmune disease incidence and symptoms.

Controlled induction of immune tolerance by mesenchymal stem cells transferred by maternal microchimerism

Feto-maternal immune tolerance is established during pregnancy; however, its mechanism and maintenance remain underexplored. Here, we investigated whether mesenchymal stem/stromal cells (MSCs) as non-inherited maternal antigens (NIMAs) transferred by maternal microchimerism could induce immune tolerance. We showed that MSCs had a potential equivalent to hematopoietic stem and progenitor cells (HSPCs) to induce immune tolerance and that MSCs were essential to induce tolerance to MSC-specific antigens. Furthermore, we demonstrated that MSCs as NIMAs transferred by maternal microchimerism could induce robust immune tolerance that can be further enhanced using a drug. Our data shed light on induction of immune tolerance and serve as a foundation to develop new therapies using maternally derived cells for autoimmune or genetic diseases.

Predictors of maternal-origin microchimerism in young women in the Philippines

OBJECTIVES

Microchimerism is the presence of a small quantity of cells or DNA from a genetically distinct individual. This phenomenon occurs with bidirectional maternal-fetal exchange during pregnancy. Microchimerism can persist for decades after delivery and have long-term health implications. However, little is known about why microchimerism is detectable at varying levels in different individuals. We examine the variability and the following potential determinants of maternal-origin microchimerism (MMc) in young women in the Philippines: gestational duration (in utero exposure to MMc), history of being breastfed (postpartum exposure to MMc), maternal telomere length (maternal cells' ability to replicate and persist), and participant's pregnancies in young adulthood (effect of adding fetal-origin microchimerism to preexisting MMc).

MATERIALS AND METHODS

Data are from the Cebu Longitudinal Health and Nutrition Survey, a population-based study of infant feeding practices and long-term health outcomes. We quantified MMc using quantitative PCR (qPCR) in 89 female participants, ages 20-22, and analyzed these data using negative binomial regression.

RESULTS

In a multivariate model including all predictors, being breastfed substantially predicted decreased MMc (detection rate ratio = 0.15, p = 0.007), and there was a trend of decreasing MMc in participants who had experienced more pregnancies (detection rate ratio = 0.55, p = 0.057).

DISCUSSION

These results might be explained by breastfeeding having lasting impact on immune regulatory networks, thus reducing MMc persistence. MMc may also decrease in response to the introduction of fetal-origin microchimerism with pregnancies experienced in adulthood.

Can some microbes promote host stress and benefit evolutionarily from this strategy?

Microbes can influence host physiology and behavior in many ways. Here we review evidence suggesting that some microbes can contribute to host stress (and other microbes can contribute to increased resilience to stress). We explain how certain microbes, which we call "stress microbes," can potentially benefit evolutionarily from inducing stress in a host, gaining access to host resources that can help fuel rapid microbial replication by increasing glucose levels in the blood, increasing intestinal permeability, and suppressing the immune system. Other microbes, which we term "resilience microbes," can potentially benefit from making hosts more resilient to stress. We hypothesize that "stress microbes" use a fast life history strategy involving greater host exploitation while "resilience microbes" use a slow life history strategy characterized by more aligned evolutionary interests with the host. In this paper, we review the evidence that microbes affect host stress and explain the evolutionary pressures that could lead microbes to manipulate host stress, discuss the physiological mechanisms that are known to be involved in both stress and microbial activity, and provide some testable predictions that follow from this hypothesis.

Costs of reproduction and ageing in the human female

Evolutionary theories of ageing point to reproduction as a significant factor to consider when asking why ageing occurs and why there is inter-individual variation in its progression. Reproduction in human females is costly, in terms of energy, nutrients and metabolic adjustments. Thus, it is expected that women who experienced high reproductive effort resulting from multiple reproductive events will age faster. However, the evidence for long-term negative effects of reproduction is not conclusive. The lack of understanding of whether there are trade-offs between reproduction and ageing in women is partly due to methodological challenges. The costs of reproduction are often calculated based only on parity, while other elements contributing to these costs (e.g. breastfeeding, timing of reproduction) are neglected, which may significantly underestimate the total costs and obscure the all-important inter-individual variation in such costs. Costs must be evaluated in relation to individual characteristics, including developmental conditions, nutritional status and social support that a mother receives during reproduction. Furthermore, ageing and health must be assessed based on comprehensive markers rather than arbitrarily assembled variables. Finally, longitudinal rather than cross-sectional studies and new statistical approaches are needed to reveal how much of a decline in health and progressing ageing can actually be attributed to past reproductive processes. This article is part of the theme issue 'Evolution of the primate ageing process'.

Life, death, and self: Fundamental questions of primitive cognition viewed through the lens of body plasticity and synthetic organisms

Central to the study of cognition is being able to specify the Subject that is making decisions and owning memories and preferences. However, all real cognitive agents are made of parts (such as brains made of cells). The integration of many active subunits into a coherent Self appearing at a larger scale of organization is one of the fundamental questions of evolutionary cognitive science. Typical biological model systems, whether basal or advanced, have a static anatomical structure which obscures important aspects of the mind-body relationship. Recent advances in bioengineering now make it possible to assemble, disassemble, and recombine biological structures at the cell, organ, and whole organism levels. Regenerative biology and controlled chimerism reveal that studies of cognition in intact, "standard", evolved animal bodies are just a narrow slice of a much bigger and as-yet largely unexplored reality: the incredible plasticity of dynamic morphogenesis of biological forms that house and support diverse types of cognition. The ability to produce living organisms in novel configurations makes clear that traditional concepts, such as body, organism, genetic lineage, death, and memory are not as well-defined as commonly thought, and need considerable revision to account for the possible spectrum of living entities. Here, I review fascinating examples of experimental biology illustrating that the boundaries demarcating somatic and cognitive Selves are fluid, providing an opportunity to sharpen inquiries about how evolution exploits physical forces for multi-scale cognition. Developmental (pre-neural) bioelectricity contributes a novel perspective on how the dynamic control of growth and form of the body evolved into sophisticated cognitive capabilities. Most importantly, the development of functional biobots - synthetic living machines with behavioral capacity - provides a roadmap for greatly expanding our understanding of the origin and capacities of cognition in all of its possible material implementations, especially those that emerge de novo, with no lengthy evolutionary history of matching behavioral programs to bodyplan. Viewing fundamental questions through the lens of new, constructed living forms will have diverse impacts, not only in basic evolutionary biology and cognitive science, but also in regenerative medicine of the brain and in artificial intelligence.

The maternal brain: Region-specific patterns of brain aging are traceable decades after childbirth

Pregnancy involves maternal brain adaptations, but little is known about how parity influences women's brain aging trajectories later in life. In this study, we replicated previous findings showing less apparent brain aging in women with a history of childbirths, and identified regional brain aging patterns linked to parity in 19,787 middle- and older-aged women. Using novel applications of brain-age prediction methods, we found that a higher number of previous childbirths were linked to less apparent brain aging in striatal and limbic regions. The strongest effect was found in the accumbens-a key region in the mesolimbic reward system, which plays an important role in maternal behavior. While only prospective longitudinal studies would be conclusive, our findings indicate that subcortical brain modulations during pregnancy and postpartum may be traceable decades after childbirth.

Regulation of maternal-fetal metabolic communication

Pregnancy may be the most nutritionally sensitive stage in the life cycle, and improved metabolic health during gestation and early postnatal life can reduce the risk of chronic disease in adulthood. Successful pregnancy requires coordinated metabolic, hormonal, and immunological communication. In this review, maternal-fetal metabolic communication is defined as the bidirectional communication of nutritional status and metabolic demand by various modes including circulating metabolites, endocrine molecules, and other secreted factors. Emphasis is placed on metabolites as a means of maternal-fetal communication by synthesizing findings from studies in humans, non-human primates, domestic animals, rabbits, and rodents. In this review, fetal, placental, and maternal metabolic adaptations are discussed in turn. (1) Fetal macronutrient needs are summarized in terms of the physiological adaptations in place to ensure their proper allocation. (2) Placental metabolite transport and maternal physiological adaptations during gestation, including changes in energy budget, are also discussed. (3) Maternal nutrient limitation and metabolic disorders of pregnancy serve as case studies of the dynamic nature of maternal-fetal metabolic communication. The review concludes with a summary of recent research efforts to identify metabolites, endocrine molecules, and other secreted factors that mediate this communication, with particular emphasis on serum/plasma metabolomics in humans, non-human primates, and rodents. A better understanding of maternal-fetal metabolic communication in health and disease may reveal novel biomarkers and therapeutic targets for metabolic disorders of pregnancy.

Individuals, Boundaries, and Graft-versus-Host Disease

Hematopoietic cell transplantation generates new individuals, transplant chimeras, composed of 2 genetic partners-the patient and donor-derived cells-no longer restricted by their original genomes. Interactions of donor-derived and recipient cells occur prominently at the boundary of the recipient with a third partner, the microbiome, in particular skin and intestinal tract, leading to disruption of microbiome homeostasis. These interactions of donor and patient cells at the boundary set the stage for the development of graft-versus-host disease, an expression of the defense of individuality by recipient and donor. Establishment of tolerance and return of homeostasis at the boundary will allow for the survival of the new integrated, physiologic individual.

Fetal Cell Microchimerism; Normal and Immunocompromised Gestations in Mice

Objective: To compare fetal cell microchimerism in normal and immunocompromised gestations. Materials and methods: The study consists of two groups of mature female mice. In the control group and the immunocompromised study group, 5 mg of saline and cyclosporine were injected intraperitoneally, respectively. In the second step, all female mice were mated with "Actine-Luc (+) green fluorescent protein (GFP)" transgenic male mice. Immunohistochemical studies (ALPL-antiluciferase, cytokeratin-antiluciferase, and CD 105-antiluciferase) were carried out on maternal liver, skin, and lung tissues at 6-7th and 14-15th gestational days, and postpartum 3-4th, 12th, and 18-24 months. Results: GFP (+) cells were detected in maternal liver and skin but not in lung tissue. Liver was the most affected tissue. GFP was found to be more intense in the immunocompromised group. Conclusion: Fetal microchimerism was demonstrated in maternal liver and skin and found to be more intensive in the immunocompromised group.

Isolation and Characterization of a Fetal-Maternal Microchimeric Stem Cell Population in Maternal Hair Follicles Long after Parturition

Fetal-maternal microchimerism describes the acquisition of fetal stem cells (FSC) by the mother during pregnancy and their long-term persistence after parturition. FSC may engraft in a variety of maternal tissues especially if there is organ/tissue injury, but their role and mechanism of persistence still remains elusive. Clinical applications due to their pluripotency, immunomodulatory effects and accessibility make them good candidates for ex-vivo manipulation and autologous therapies. The hair follicles contain a distinctive niche for pluripotent stem cells (PSC). To date, there is no published evidence of fetal microchimerism in the hair follicle. In our study, follicular unit extraction (FUE) technique allowed easy stem cell cultures to be obtained while simple hair follicle removal by pull-out technique failed to generate stem cells in culture. We identified microchimeric fetal stem cells within the primitive population of maternal stem cells isolated from the hair follicles with typical mesenchymal phenotype, expression of PSC genes and differentiation potential towards osteocytes, adypocites and chondrocytes. This is the first study to isolate fetal microchimeric stem cells in adult human hair long after parturition. We presume a sanctuary partition mechanism with PSC of the mother deposited during early embryogenesis could explain their long-term persistence.

Towards an understanding of women's brain aging: the immunology of pregnancy and menopause

Women are at significantly greater risk of developing Alzheimer's disease and show higher prevalence of autoimmune conditions relative to men. Women's brain health is historically understudied, and little is therefore known about the mechanisms underlying epidemiological sex differences in neurodegenerative diseases, and how female-specific factors may influence women's brain health across the lifespan. In this review, we summarize recent studies on the immunology of pregnancy and menopause, emphasizing that these major immunoendocrine transition phases may play a critical part in women's brain aging trajectories.

Cooperation and conflict in human pregnancy

For many humans living today, obstetric care begins early in pregnancy, and most babies are born in hospitals. These are precautionary measures. Medical complications during the brief nine months of pregnancy are such a common part of human experience that we rarely ask ourselves why gestation does not always proceed as smoothly and reliably as the lifelong beating of our heart or filtration of blood by our kidneys. The birth of a healthy child is central to reproductive fitness and must have been subject to strong natural selection. Why then should placentas be less reliable organs than hearts or kidneys? Why should maternal hearts and kidneys be more subject to catastrophic failures during pregnancy than at other times? A crucial contrast distinguishes obstetrics from cardiology and nephrology. The coordinated activities of heart and kidneys take place within an individual comprised of genetically largely identical cells, whereas pregnancy involves an interaction between genetically-distinct individuals whose cooperation is obviated by evolutionary conflicts of interest.

Natural human chimeras: A review

The term chimera has been borrowed from Greek mythology and has a long history of use in biology and genetics. A chimera is an organism whose cells are derived from two or more zygotes. Recipients of tissue and organ transplants are artificial chimeras. This review concerns natural human chimeras. The first human chimera was reported in 1953. Natural chimeras can arise in various ways. Fetal and maternal cells can cross the placental barrier so that both mother and child may become microchimeras. Two zygotes can fuse together during an early embryonic stage to form a fusion chimera. Most chimeras remain undetected, especially if both zygotes are of the same genetic sex. Many are discovered accidently, for example, during a routine blood group test. Even sex-discordant chimeras can have a normal male or female phenotype. Only 28 of the 50 individuals with a 46,XX/46,XY karyotype were either true hermaphrodites or had ambiguous genitalia. Blood chimeras are formed by blood transfusion between dizygotic twins via the shared placenta and are more common than was once assumed. In marmoset monkey twins the exchange via the placenta is not limited to blood but can involve other tissues, including germ cells. To date there are no examples in humans of twin chimeras involving germ cells. If human chimeras are more common than hitherto thought there could be many medical, social, forensic, and legal implications. More multidisciplinary research is required for a better understanding of this fascinating subject.

Prevalence of red-blood-cell and non-red-blood-cell-targeted autoantibodies in alloimmunized postpartum women

BACKGROUND AND OBJECTIVES

Alloantibodies against red-blood-cell (RBC) antigens often coincide with alloantibodies against leucocytes and platelets and sometimes with autoantibodies towards various antigens. Chimerism may be one of the factors responsible for the combination of allo- and autoantibodies. Women with alloantibodies against RBC antigens causing haemolytic disease of the fetus and neonate may need to receive intrauterine transfusions. These transfusions increase not only maternal antibody formation but also fetomaternal bleeding and may enhance fetal chimerism. We determined the prevalence of and risk factors for autoantibodies against some common clinical target antigens, in alloimmunized women after IUT.

MATERIALS AND METHODS

We tested for autoantibodies against RBC, anti-thyroid peroxidase, anti-extractable nuclear antigens, anti-cyclic citrullinated proteins and anti-tissue transglutaminase. Women with and without autoantibodies were compared for age; number of RBC alloantibodies, pregnancies and IUTs, and other factors that may play a role in immunization.

RESULTS

Non-RBC-targeted autoantibodies were present in 40 of 258 tested women (15·5%, with 90% anti-TPO specificity), comparable to the prevalence reported in healthy Dutch women of these ages. Surprisingly, compared with women who had a single RBC alloantibody, a significantly higher proportion of women with multiple RBC alloantibodies had autoantibodies (5·3% and 18·4%, respectively; odds ratio 4·06, 95% CI: 1·20-13·7). Other characteristics of women with and without autoantibodies were not different.

CONCLUSION

Multiple RBC alloantibodies after extensive allogeneic exposure during pregnancy and presumed increased fetomaternal chimerism are not associated with (selected) autoantibodies. Lack of allo-RBC multi-responsiveness seems associated with decreased auto(-TPO) antibody formation.