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Adaptations of the immune system throughout gestation have been proposed as important mechanisms regulating successful pregnancy. Dysregulation of the maternal immune system has been associated with adverse maternal and fetal outcomes. To translate findings from mechanistic preclinical studies to human pregnancies, studies of serum immune markers are the mainstay. The design and interpretation of human biomarker studies require additional insights in the trajectories and drivers of peripheral immune markers. The current study mapped maternal inflammatory markers (C-reactive protein (CRP), interleukin (IL)-1β, IL-6, IL-17A, IL-23, interferon- γ ) during pregnancy and investigated the impact of demographic, environmental and genetic drivers on maternal inflammatory marker levels in four multi-ethnic and socio-economically diverse population-based cohorts with more than 12,000 pregnant participants. Additionally, pregnancy inflammatory markers were compared to pre-pregnancy levels. Cytokines showed a high correlation with each other, but not with CRP. Inflammatory marker levels showed high variability between individuals, yet high concordance within an individual over time during and pre-pregnancy. Pre-pregnancy body mass index (BMI) explained more than 9.6% of the variance in CRP, but less than 1% of the variance in cytokines. The polygenic score of CRP was the best predictor of variance in CRP (>14.1%). Gestational age and previously identified inflammation drivers, including tobacco use and parity, explained less than 1% of variance in both cytokines and CRP. Our findings corroborate differential underlying regulatory mechanisms of CRP and cytokines and are suggestive of an individual inflammatory marker baseline which is, in part, genetically driven. While prior research has mainly focused on immune marker changes throughout pregnancy, our study suggests that this field could benefit from a focus on intra-individual factors, including metabolic and genetic components.

Associations between antenatal SARS-CoV-2 infection and pregnancy outcomes have been conflicting and the role of the immune system is currently unclear. This prospective cohort study investigated the interaction of antenatal SARS-CoV-2 infection, changes in cytokine and HS-CRP levels, birthweight and gestational age at birth. 2352 pregnant participants from New York City (2020-2022) were included. Plasma levels of interleukin (IL)-1β, IL-6, IL-17A and high-sensitivity C-reactive protein (HS-CRP) were quantified in blood specimens obtained across pregnancy. Quantile and linear regression models were conducted to 1) assess the impact of antenatal SARS-CoV-2 infection, overall and by timing of detection of SARS-CoV-2 positivity (< 20 weeks versus ≥ 20 weeks), on birthweight and gestational age at delivery; 2) examine the relationship between SARS-CoV-2 infection and maternal immune changes during pregnancy. All models were adjusted for maternal demographic and obstetric factors and pandemic timing. Birthweight models were additionally adjusted for gestational age at delivery and fetal sex. Immune marker models were also adjusted for gestational age at specimen collection and multiplex assay batch. 371 (15.8%) participants were infected with SARS-CoV-2 during pregnancy, of which 98 (26.4%) were infected at < 20 weeks gestation. Neither SARS-CoV-2 infection in general nor in early or late pregnancy was associated with lower birthweight nor earlier gestational age at delivery. Further, we did not observe cytokine or HS-CRP changes in response to SARS-CoV-2 infection and thus found no evidence to support a potential association between immune dysregulation and the diversity in pregnancy outcomes following infection., Competing Interests: Declaration of Competing Interest The Icahn School of Medicine at Mount Sinai has filed patent applications relating to SARS-CoV-2 serological assays and NDV-based SARS-CoV-2 vaccines which list Florian Krammer as co-inventor. Mount Sinai has spun out a company, Kantaro, to market serological tests for SARS-CoV-2. Florian Krammer has consulted for Merck and Pfizer (before 2020), and is currently consulting for Pfizer, Seqirus, 3rd Rock Ventures and Avimex and he is a co-founder and scientific advisory board member of CastleVax. The Krammer laboratory is also collaborating with Pfizer on animal models of SARS-CoV-2. The other authors have nothing to report. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Disturbances in T-cells, specifically the Th17/Treg balance, have been implicated in adverse pregnancy outcomes. We investigated these two T-cell populations following pre-pregnancy and pregnancy SARS-CoV-2 infection and COVID-19 vaccination in 351 participants from a pregnancy cohort in New York City (Generation C; 2020-2022). SARS-CoV-2 infection status was determined via laboratory or medical diagnosis and COVID-19 vaccination status via survey and electronic medical records data. Peripheral blood mononuclear cells (PBMCs) were collected at routine prenatal visits throughout gestation (median 108 days; IQR 67-191 days) with repeated measures for 104 participants (29.6%). T-cell populations CD4+/CD3+, Th17/CD4+, Treg/CD4+ and the Th17/Treg ratio were quantified using flow cytometry. Results showed that inter-individual differences are a main influencing factor in Th17 and Treg variance, however total variance explained remained small (R 2  = 15-39%). Overall, Th17 and Treg populations were not significantly affected by SARS-CoV-2 infection during pregnancy in adjusted linear mixed models ( p >0.05), however comparison of repeated measures among SARS-CoV-2 infected participants and non-infected controls suggests a relative increase of the Th17/Treg ratio following infection. In addition, the Th17/Treg ratio was significantly higher after SARS-CoV-2 infection prior to pregnancy (10-138 weeks) compared to controls (β=0.48, p =0.003). COVID-19 vaccination was not associated with Th17 and Treg cells. Our findings suggest an impact of SARS-CoV-2 infection on the Th17/Treg ratio, likely depending on severity of infection, yet the observed trends and their potential consequences for pregnancy outcomes require further investigation. Our study contributes to growing evidence that COVID-19 vaccination during pregnancy does not lead to an exacerbated immune response., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Gigase, Graziani, Castro, Lesseur, Rommel, Flores, Perez-Rodriguez, Dolan, Stone, Janevic, Lieb, Bergink and de Witte.)

Numerous studies reported an increase of postpartum mood symptoms during the COVID-19 pandemic. Yet, the link between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and perinatal mental health is less well understood. We investigated the associations between prenatal SARS-CoV-2 infection and postpartum depressive and anxiety symptoms, including examinations of infection timing and pandemic timeline. We included 595 participants from Generation C, a prospective pregnancy cohort in New York City (2020-2022). Prenatal SARS-CoV-2 infection was determined via laboratory or medical diagnosis. Depression and anxiety symptoms were measured 4-12 weeks postpartum using the Edinburgh Postnatal Depression Scale (EPDS) and Generalized Anxiety Disorder questionnaire (GAD), respectively. Quantile regressions were conducted with prenatal SARS-CoV-2 infection as exposure and continuously measured EPDS and GAD scores as outcomes. We reran the analyses in those with COVID-19-like symptoms in the trimester during which infection occurred. 120 (20.1%) participants had prenatal SARS-CoV-2 infection. After adjusting for socio-demographic, obstetric and other maternal health factors, prenatal SARS-CoV-2 infection was associated with higher median postpartum anxiety scores (b = 0.55, 95% CI = 0.15; 0.96). Late gestation infection (b = 1.15, 95% CI = 0.22; 2.09) and symptomatic infection (b = 1.15, 95% CI = 0.12; 2.18) were also associated with higher median postpartum anxiety scores. No associations were found with depressive symptoms. The associations were not moderated by time since the start of the pandemic. This study suggests that prenatal SARS-CoV-2 infection increases the risk of postpartum anxiety symptoms among participants reporting median anxiety symptoms. Given that this association was not affected by pandemic timing and that SARS-CoV-2 transmission continues, individuals infected with SARS-CoV-2 during pregnancy should be monitored for postpartum anxiety symptoms., Competing Interests: Declaration of competing interest The Icahn School of Medicine at Mount Sinai has filed patent applications relating to SARS-CoV-2 serological assays and NDV-based SARS-CoV-2 vaccines which list Florian Krammer as co-inventor. Mount Sinai has spun out a company, Kantaro, to market serological tests for SARS-CoV-2. Florian Krammer has consulted for Merck and Pfizer (before 2020), and is currently consulting for Pfizer, Seqirus, 3rd Rock Ventures and Avimex and he is a co-founder and scientific advisory board member of CastleVax. The Krammer laboratory is also collaborating with Pfizer on animal models of SARS-CoV-2. M. Mercedes Perez-Rodriguez has received consulting fees from Alkermes, Inc and Neurocrine Biosciences, for work unrelated to this manuscript. The other authors have nothing to report., (Copyright © 2023. Published by Elsevier Ltd.)

Objective: Exposure to infections during pregnancy may be a potential risk factor for later psychopathology, but large-scale epidemiological studies investigating associations between prenatal infection and long-term offspring behavioral problems in the general population are scarce. In our study, we aimed to investigate the following: (1) the association between prenatal infection and adolescent behavior, (2) putative underlying pathways (mediation), and (3) "second hits" interacting with prenatal infection to increase the risk of adolescent behavior problems (moderation)., Method: Our study was embedded in a prospective Dutch pregnancy cohort (Generation R; n = 2,213 mother-child dyads). We constructed a comprehensive prenatal infection score comprising common infections for each trimester of pregnancy. At age 13 to 16 years, we assessed total, internalizing, and externalizing problems, and autistic traits using the Child Behavioral Checklist and the Social Responsiveness Scale, respectively. We investigated maternal lifestyle and nutrition, perinatal factors (placental health and delivery outcomes), and child health (lifestyle, traumatic events, infections) as mediators and moderators., Results: We observed associations of prenatal infection with adolescent total behavioral, internalizing, and externalizing problems. The association between prenatal infection and internalizing problems was moderated by higher levels of maternal psychopathology, alcohol and tobacco use, and a higher number of traumatic childhood events. We found no association between prenatal infection and autistic traits. Yet, children exposed to prenatal infections and maternal substance use, and/or traumatic childhood events, had a higher risk of autistic traits in adolescence., Conclusion: Prenatal infection may be a risk factor for later psychiatric problems as well as a disease primer making individuals susceptible to other hits later in life., Study Preregistration Information: Prenatal maternal infection and adverse neurodevelopment: a structural equation modelling approach to downstream environmental hits; https://osf.io/cp85a; cp85a., Diversity & Inclusion Statement: We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. We worked to ensure sex and gender balance in the recruitment of human participants., (Copyright © 2023 American Academy of Child and Adolescent Psychiatry. Published by Elsevier Inc. All rights reserved.)

Microglia, the immune cells of the brain, are increasingly implicated in neurodegenerative disorders through genetic studies. However, how genetic risk factors for these diseases are related to microglial gene expression, microglial function, and ultimately disease, is still largely unknown. Microglia change rapidly in response to alterations in their cellular environment, which is regulated through changes in transcriptional programs, which are as yet poorly understood. Here, we compared the effects of a set of inflammatory and restorative stimuli (lipopolysaccharide, interferon-gamma, resiquimod, tumor necrosis factor-alpha, adenosine triphosphate, dexamethasone, and interleukin-4) on human microglial cells from 67 different donors (N = 398 samples) at the gene and transcript level. We show that microglia from different anatomical brain regions show distinct responses to inflammatory stimuli. We observed a greater overlap between human stimulated microglia and human monocytes than with mouse microglia. We define specific microglial signatures across conditions which are highly relevant for a wide range of biological functions and complex human diseases. Finally, we used our stimulation signatures to interpret associations from Alzheimer's disease (AD) genetic studies and microglia by integrating our inflammatory gene expression profiles with common genetic variants to map cis -expression QTLs (eQTLs). Together, we provide the most comprehensive transcriptomic database of the human microglia responsome., Highlights: RNA-sequencing of 398 human microglial samples exposed to six different triggers.Microglia from different anatomical regions show distinct stimulation responses.Responses in human microglia show a greater overlap with human monocytes than murine microglia.Mapping of response Quantitative Trait Loci identifies interactions between genotype and effect of stimulation on gene expression.Our atlas provides a reference map for interpreting microglia signatures in health and disease.

We examined differences in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody responses in pregnant individuals with natural, vaccine-induced, or combined immunity. Participants had live or nonlive births between 2020 and 2022, were seropositive (SARS-CoV-2 spike protein, anti-S), and had available mRNA vaccination and infection information (n=260). We compared titer levels among three immunity profiles: 1) natural immunity (n=191), 2) vaccine-induced immunity (n=37), and 3) combined immunity (ie, natural and vaccine-induced immunity; n=32). We applied linear regression to compare anti-S titers between the groups, controlling for age, race and ethnicity, and time between vaccination or infection (whichever came last) and sample collection. Anti-S titers were 57.3% and 94.4% lower among those with vaccine-induced and natural immunity, respectively, compared with those with combined immunity ( P <.001, P =.005)., Competing Interests: Financial Disclosure Elizabeth A. Howell disclosed receiving payment from the American Heart Association Health Equity Research Network (HERN) on Disparities in Maternal-Infant Health Outcomes via University of Alabama at Birmingham Coordinating Center and the Vermont Oxford Network Health Equity Board. The Icahn School of Medicine at Mount Sinai has filed patent applications relating to influenza virus vaccines, SARS-CoV-2 serological assays, and SARS-CoV-2 vaccines, which list Florian Krammer and Daniel Stadlbauer as co‐inventor. Mount Sinai has spun out companies, Kantaro and Castlevax, to market the SARS-CoV-2 related technologies. Florian Krammer has consulted for Merck and Pfizer (before 2020), and is currently consulting for Pfizer, Seqirus, 3rd Rock Ventures, GSK and Avimex. The Krammer laboratory is also collaborating with Pfizer on animal models of SARS‐CoV‐2 and with Dynavax on universal influenza virus vaccines. They are also receiving grant/contract funding from NIH, the Bill and Melinda Gates Foundation, and FluLab. Siobhan M. Dolan received payment from American Imaging Management, Inc. They serve as an expert in OBGYN and Genetics on their insurance coverage for the genetic testing review panel. Initial assay development work in the Krammer laboratory was partially supported by the NIAID Centers of Excellence for Influenza Research and Surveillance (CEIRS) contract HHSN272201400008C (FK, for reagent generation), Collaborative Influenza Vaccine Innovation Centers (CIVIC) contract 75N93019C00051 (FK, for reagent generation), the generous support of the JPB foundation, the Open Philanthropy Project (#2020–215611) and other philanthropic donations. These funding sources were not involved in the current study. The other authors did not report any potential conflicts of interest., (Copyright © 2023 by the American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.)

Objectives: High plasma copper (Cu) and low zinc (Zn) levels have been associated with depression. However, most studies used low sample sizes and a cross-sectional design, and perinatal data are scarce. We investigated the possible association between pregnancy-specific psychological distress and the plasma CuZn ratio using a prospective design., Methods: Pregnancy-specific distress symptoms were assessed at each trimester by means of the Tilburg Pregnancy Distress Scale, negative affect subscale, in 2036 pregnant women. Cu and Zn were assessed at 12 wk of gestation in plasma samples by inductively coupled plasma mass spectrometry. Growth mixture modeling determined trajectories of women's pregnancy-specific negative affect (P-NA) symptoms, which were entered in a multiple logistic regression analysis as dependent variable and the CuZn ratio as independent variable., Results: Two P-NA symptom classes were found: 1) persistently low (n = 1820) and 2) persistently high (n = 216). A higher CuZn ratio was independently associated with persistently high P-NA symptom scores (odds ratio = 1.52; 95% confidence interval, 1.13-2.04) after adjustment for confounders. A sensitivity analysis was performed excluding all women with high P-NA scores at 12 wk of gestation (>1 SD above the mean P-NA score). In the 1719 remaining women, a higher CuZn ratio significantly predicted the development of increasing P-NA symptom scores after adjustment for confounders (odds ratio = 1.40; 95% confidence interval, 1.04-1.95)., Conclusions: A higher CuZn plasma ratio is an independent determinant of developing pregnancy-specific distress symptoms throughout pregnancy, suggesting that micronutrients could be used as novel biomarkers for psychological distress research of perinatal mood disorders., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Background: Neuroinflammatory processes have been hypothesized to play a role in the pathogenesis of psychiatric and neurological diseases. Studies on this topic often rely on analysis of inflammatory biomarkers in peripheral blood. Unfortunately, the extent to which these peripheral markers reflect inflammatory processes in the central nervous system (CNS) is unclear., Methods: We performed a systematic review and found 29 studies examining the association between inflammatory marker levels in blood and cerebrospinal (CSF) samples. We performed a random effects meta-analysis of 21 studies (pooled n = 1679 paired samples) that reported the correlation of inflammatory markers in paired blood-CSF samples., Results: A qualitative review revealed moderate to high quality of included studies with the majority of studies reporting no significant correlation of inflammatory markers between paired blood-CSF. Meta-analyses revealed a significant low pooled correlation between peripheral and CSF biomarkers (r = 0.21). Meta-analyses of individual cytokines revealed a significant pooled correlation for IL-6 (r = 0.26) and TNFα (r = 0.3) after excluding outlier studies, but not for other cytokines. Sensitivity analyses showed that correlations were highest among participants with a median age above 50 (r = 0.46) and among autoimmune disorder patients (r = 0.35)., Conclusion: This systematic review and meta-analysis revealed poor correlation between peripheral and central inflammatory markers in paired blood-CSF samples, with increased correlations in certain study populations. Based on the current findings, peripheral inflammatory markers are a poor reflection of the neuroinflammatory profile., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Research suggest prenatal vaccination against coronavirus disease-19 (COVID-19) is safe. However, previous studies utilized retrospectively collected data or examined late pregnancy vaccinations. We investigated the associations of COVID-19 vaccination throughout pregnancy with delivery and neonatal outcomes. We included 1,794 mother-neonate dyads enrolled in the Generation C Study with known prenatal COVID-19 vaccination status and complete covariate and outcome data. We used multivariable quantile regressions to estimate the effect of prenatal COVID-19 vaccination on birthweight, delivery gestational age, and blood loss at delivery; and Poisson generalized linear models for Caesarean delivery (CD) and Neonatal Intensive Care Unit (NICU) admission. Using the above methods, we estimated effects of trimester of vaccine initiation on these outcomes. In our sample, 13.7% (n = 250) received at least one prenatal dose of any COVID-19 vaccine. Vaccination was not associated with birthweight (β = 12.42 g [-90.5, 114.8]), gestational age (β = 0.2 days [-1.1, 1.5]), blood loss (β = -50.6 ml [-107.0, 5.8]), the risks of CD (RR = 0.8; [0.6, 1.1]) or NICU admission (RR = 0.9 [0.5, 1.7]). Trimester of vaccine initiation was also not associated with these outcomes. Our findings suggest that there is no associated risk between prenatal COVID-19 vaccination and adverse delivery and neonatal outcomes in a cohort sample from NYC., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)

Pregnant women may be specifically prone to experience pregnancy-specific distress, which has been associated with adverse maternal, pregnancy and child outcomes. Accurately identifying pregnancy-specific distress is thus crucial. The Tilburg Pregnancy Distress Scale (TPDS) - translated into many different languages - was previously developed to measure pregnancy-specific distress, resulting in a 16-item screening scale with a partner involvement dimension (PI) and a negative affect dimension (NA). A critical evaluation of the psychometric properties of the TPDS-NA items and feedback from pregnant women over the last decade has led to the need to revise the TPDS. Therefore, in the current study, we describe the procedure for revision and evaluate the psychometric properties of the revised TPDS (TPDS-R). More specifically, we describe the revision of the TPDS-R-PI (4 items) and the TPDS-R-NA (10 items: five-item pregnancy and five-item childbirth subcomponent). A sample of 1081 pregnant women participating in the Brabant Study completed the TPDS-R at 12, 20 and 28 weeks of pregnancy. An exploratory factor analysis and confirmatory factor analysis, descriptive statistics and repeated measures ANOVA demonstrated good test-retest reliability, concurrent validity, internal consistency, and construct validity of the TPDS-R. The TPDS-R provides a robust screening tool to accurately identify pregnant women at risk of pregnancy-specific distress., Competing Interests: Declaration of competing interest Each author confirmed that there is no conflict of interest between the author and the study., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Introduction: Maternal SARS-CoV-2 infection during pregnancy is associated with adverse pregnancy outcomes and can have effects on the placenta, even in the absence of severe disease or vertical transmission to the fetus. This study aimed to evaluate histopathologic and molecular effects in the placenta after SARS-CoV-2 infection during pregnancy., Methods: We performed a study of 45 pregnant participants from the Generation C prospective cohort study at the Mount Sinai Health System in New York City. We compared histologic features and the expression of 48 immune and trophoblast genes in placentas delivered from 15 SARS-CoV-2 IgG antibody positive and 30 IgG SARS-CoV-2 antibody negative mothers. Statistical analyses were performed using Fisher's exact tests, Spearman correlations and linear regression models., Results: The median gestational age at the time of SARS-CoV-2 IgG serology test was 35 weeks. Two of the IgG positive participants also had a positive RT-PCR nasal swab at delivery. 82.2% of the infants were delivered at term (≥37 weeks), and gestational age at delivery did not differ between the SARS-CoV-2 antibody positive and negative groups. No significant differences were detected between the groups in placental histopathology features. Differential expression analyses revealed decreased expression of two trophoblast genes (PSG3 and CGB3) and increased expression of three immune genes (CXCL10, TLR3 and DDX58) in placentas delivered from SARS-CoV-2 IgG positive participants., Discussion: SARS-CoV-2 infection during pregnancy is associated with gene expression changes of immune and trophoblast genes in the placenta at birth which could potentially contribute to long-term health effects in the offspring., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Microglia have emerged as important players in brain aging and pathology. To understand how genetic risk for neurological and psychiatric disorders is related to microglial function, large transcriptome studies are essential. Here we describe the transcriptome analysis of 255 primary human microglial samples isolated at autopsy from multiple brain regions of 100 individuals. We performed systematic analyses to investigate various aspects of microglial heterogeneities, including brain region and aging. We mapped expression and splicing quantitative trait loci and showed that many neurological disease susceptibility loci are mediated through gene expression or splicing in microglia. Fine-mapping of these loci nominated candidate causal variants that are within microglia-specific enhancers, finding associations with microglial expression of USP6NL for Alzheimer's disease and P2RY12 for Parkinson's disease. We have built the most comprehensive catalog to date of genetic effects on the microglial transcriptome and propose candidate functional variants in neurological and psychiatric disorders., (© 2022. The Author(s), under exclusive licence to Springer Nature America, Inc.)

Different lines of evidence support a causal role for microglia in the pathogenesis of schizophrenia. However, how schizophrenia patient-derived microglia are affected at the phenotypic and functional level is still largely unknown. We used a recently described model to induce patient-derived microglia-like cells and used this to analyze changes in the molecular phenotype and function of myeloid cells in schizophrenia. We isolated monocytes from twenty recent-onset schizophrenia patients and twenty non-psychiatric controls. We cultured the cells towards an induced microglia-like phenotype (iMG), analyzed the phenotype of the cells by RNA sequencing and mass cytometry, and their response to LPS. Mass cytometry showed a high heterogeneity of iMG in cells derived from patients as well as controls. The prevalence of two iMG clusters was significantly higher in schizophrenia patients (adjusted p-value < 0.001). These subsets are characterized by expression of ApoE, Ccr2, CD18, CD44, and CD95, as well as IRF8, P2Y 12, Cx3cr1 and HLA-DR. In addition, we found that patient-derived iMG show an enhanced response to LPS, with increased secretion of TNF-α. Further studies are needed to replicate these findings, to determine whether similar subclusters are present in schizophrenia patients in vivo, and to address how these subclusters are related to the increased response to LPS, as well as other microglial functions., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Bipolar disorder (BD) is a complex neurobiological disease. It is likely that both neurons and glial cells are affected in BD, yet how these cell types are changed at the structural and functional level is still largely unknown. In this review we provide an overview of postmortem studies analyzing structural cellular changes in BD, including the density, number and size of neurons and glia. We categorize the results per cell-type and validate outcome measures per brain region. Despite variations by brain region, outcome measure and methodology, several patterns could be identified. Total neuron, total glia, and cell subtypes astrocyte, microglia and oligodendrocyte presence appears unchanged in the BD brain. Interneuron density may be decreased across various cortical areas, yet findings of interneuron subpopulations show discrepancies. This structural review brings to light issues in validation and replication. Future research should therefore prioritize the validation of existing studies in order to increasingly refine the conceptual models of BD., (Copyright © 2019 Elsevier Ltd. All rights reserved.)