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In vivo immune signatures of healthy human pregnancy: Inherently inflammatory or anti-inflammatory?

  • Caroline Graham,

    Affiliation Department of Immunology, University of Manitoba, Winnipeg, Manitoba, Canada

  • Rishma Chooniedass,

    Affiliation Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, Manitoba, Canada

  • William P. Stefura,

    Affiliation Department of Immunology, University of Manitoba, Winnipeg, Manitoba, Canada

  • Allan B. Becker,

    Affiliations Department of Immunology, University of Manitoba, Winnipeg, Manitoba, Canada, Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, Manitoba, Canada, Children’s Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada

  • Malcolm R. Sears,

    Affiliation Department of Medicine, de Groote School of Medicine, McMaster University, Hamilton, Ontario, Canada

  • Stuart E. Turvey,

    Affiliation Department of Pediatrics, Child & Family Research Institute and BC Children’s Hospital, University of British Columbia, Vancouver, British Columbia, Canada

  • Piush J. Mandhane,

    Affiliation Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada

  • Padmaja Subbarao,

    Affiliation Department of Pediatrics, Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada

  • CHILD Study Investigators ,

    Membership of the CHILD Principal Investigators is provided in the Acknowledgments.

    Affiliation CHILD (Canadian Healthy Infant Longitudinal Development Study) Investigators, McMaster University, Hamilton, Canada

  • Kent T. HayGlass

    kent.hayglass@umanitoba.ca

    Affiliations Department of Immunology, University of Manitoba, Winnipeg, Manitoba, Canada, Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, Manitoba, Canada, Children’s Hospital Research Institute of Manitoba, Winnipeg, Manitoba, Canada

    ORCID http://orcid.org/0000-0002-4621-7737

In vivo immune signatures of healthy human pregnancy: Inherently inflammatory or anti-inflammatory?

  • Caroline Graham, 
  • Rishma Chooniedass, 
  • William P. Stefura, 
  • Allan B. Becker, 
  • Malcolm R. Sears, 
  • Stuart E. Turvey, 
  • Piush J. Mandhane, 
  • Padmaja Subbarao, 
  • CHILD Study Investigators, 
  • Kent T. HayGlass
PLOS
x

Abstract

Changes in maternal innate immunity during healthy human pregnancy are not well understood. Whether basal immune status in vivo is largely unaffected by pregnancy, is constitutively biased towards an inflammatory phenotype (transiently enhancing host defense) or exhibits anti-inflammatory bias (reducing potential responsiveness to the fetus) is unclear. Here, in a longitudinal study of healthy women who gave birth to healthy infants following uncomplicated pregnancies within the Canadian Healthy Infant Longitudinal Development (CHILD) cohort, we test the hypothesis that a progressively altered bias in resting innate immune status develops. Women were examined during pregnancy and again, one and/or three years postpartum. Most pro-inflammatory cytokine expression, including CCL2, CXCL10, IL-18 and TNFα, was reduced in vivo during pregnancy (20–57%, p<0.0001). Anti-inflammatory biomarkers (sTNF-RI, sTNF-RII, and IL-1Ra) were elevated by ~50–100% (p<0.0001). Systemic IL-10 levels were unaltered during vs. post-pregnancy. Kinetic studies demonstrate that while decreased pro-inflammatory biomarker expression (CCL2, CXCL10, IL-18, and TNFα) was constant, anti-inflammatory expression increased progressively with increasing gestational age (p<0.0001). We conclude that healthy resting maternal immune status is characterized by an increasingly pronounced bias towards a systemic anti-inflammatory innate phenotype during the last two trimesters of pregnancy. This is resolved by one year postpartum in the absence of repeat pregnancy. The findings provide enhanced understanding of immunological changes that occur in vivo during healthy human pregnancy.

Introduction

For healthy pregnancy to proceed to term, changes need to occur to prevent immune mediated rejection of the semi-allogenic fetus. At the same time, the immune system must maintain, or enhance, protection of mother and fetus from external pathogens. There is extensive literature concerning immunity at the maternal-fetal interface and its role in progression of fetal development [15]. Similarly, many studies have examined pathologic conditions that can arise during pregnancy (i.e. preeclampsia, infection, hypoxia), often with small, cross-sectional, healthy control groups for comparison.

Surprisingly, healthy pregnancy that leads to healthy infants has not been a major research focus and is not well understood. Publications [6] and recent NIH workshops [7, 8] identify the need for better insight into the biology of normal pregnancy. Attention needs to be given to (i) understanding maternal adaptations and (ii) creating a biological definition of an optimal pregnancy phenotype from fetal, maternal and paternal standpoints. Understanding putative changes in women’s in vivo innate immune status during normal pregnancy–the healthy phenotype–will strengthen efforts to understand linkages between in vivo maternal status and the subsequent development of healthy vs. chronic inflammatory phenotypes such as asthma or autoimmunity in children, or their mothers, later in life [913].

The changes, if any, that occur in innate immune status during a healthy pregnancy are controversial. Existing evidence supports several mutually exclusive conclusions. Some data are consistent with the concept that basal maternal systemic immunity exhibits a mild bias towards inflammatory phenotypes (hence, transiently enhancing host defense). Others support the notion that immunosuppressed phenotypes (reducing potential responses to the fetus) are normally dominant during pregnancy [14]. A third school of thought argues that innate immune function is largely unchanged in pregnant and non-pregnant women [3, 15].

Interest in healthy pregnancy is driven by at least three other rationales. Exclusion of pregnant women from clinical research, while well intentioned, can be counterproductive [7]. Their inclusion requires better understanding of maternal health norms during healthy pregnancy. Secondly, identifying and understanding differences in basal innate immune status in vivo during healthy pregnancy will provide better understanding of mechanisms that underlie difficult pregnancies [15]. Finally, with extensive efforts to link systemic innate immunity in vivo and clinical outcomes later in life for both mother and fetus [16, 17], we need to better define immunity in healthy human pregnancy as the entry point to childhood.

The Canadian Healthy Infant Longitudinal Development (CHILD) birth cohort was initiated to study the development of allergy and asthma, with a strong focus on clinical, immunologic and environmental assessments of infants and parents. The 3,624 participating infants and families are predominantly from urban centres; over 80% of the Canadian population is urban. The cohort is multicultural and ethnically varied. Its value is enhanced by extensive phenotyping of both children and parents, characterization of their environments and an extensive repository of biological samples [18].

Here we test the hypothesis that resting systemic pro-/anti-inflammatory bias in vivo is transiently shifted during pregnancy. In this longitudinal study of 251 randomly selected healthy women who gave birth to healthy infants, pairwise comparisons were used to assess innate immune biomarker levels in vivo during the second/third trimester then again at one and three years postpartum. An extensive panel of pro-inflammatory cytokines that are constitutively present in most healthy individuals (CCL2, CXCL10, CXCL8, IL-18, IL-6, and TNFα) was examined. While studies of inflammatory processes often include few or no anti-inflammatory regulators, endogenous levels of a broad panel of anti-inflammatory cytokines (IL-10, IL-1Ra, sTNF-RI, and sTNF-RII) were incorporated to provide a better immune signature of women’s health during successful pregnancy. The data reveal that extensive changes occur in vivo. Healthy pregnancy is linked to development of a constitutive systemic anti-inflammatory maternal bias that becomes increasingly intense with increasing gestational age, then self-resolves by one year postpartum.

Materials and methods

Participants

The Canadian Healthy Infant Longitudinal Development (CHILD) Study is a prospective national population-based longitudinal birth cohort of 3,624 neonates (http://www.canadianchildstudy.ca/knowledge.html) [18]. Following written, informed consent, non-fasting venous blood was obtained at the University of Manitoba recruitment site to yield plasma samples from 499 women. Median age at recruitment was 31.1 years. Women were recruited between conception and delivery, as possible, with most recruitment taking place during the second and third trimester. Inclusion criteria included uneventful pregnancy without documented concerns about hypertension, proteinuria or gestational diabetes that resulted in a healthy singleton baby. Exclusion criteria included in vitro fertilization (IVF), twins, miscarriage, intrauterine growth restriction (IUGR), clinically discernible upper respiratory tract (URT) or gastrointestinal (GI) infection within a week of study visit or repeat pregnancy evident at or within two months following one year and three year postpartum visits. This study was approved by the University of Manitoba Human Research Ethics Board.

To increase power, rather than incorporating unrelated non-pregnant female controls, a longitudinal study design was used where a woman’s status during pregnancy was compared with her own at subsequent times. Samples were obtained once at initial recruitment (a visit between gestational weeks 10–38) and again one year postpartum. Major clinical characteristics of the women studied are provided in Table 1.

251 of the mothers for whom paired plasma samples were available from prenatal (PN) and one year post-partum (1YPP) time points (n = 331) were randomly selected for analysis of in vivo pro- and anti-inflammatory cytokine expression (CCL2 and sTNF-RI). These biomarkers were chosen because published, and our own preliminary data, demonstrated that readily quantified levels are evident in >95% of healthy individuals (cf. IL-6 or IL-10 where a substantial proportion of healthy individuals exhibit sub pg/ml plasma levels). For more extensive analyses, 8 additional in vivo biomarkers were determined using approximately every second individual (n = 120) from the original study group. Investigators were blind to any immunological data at the time of randomization and sample selection.

Among women who provided plasma samples at both one and three years post-partum, (and who did not experience pregnancy in the interim) 32 were randomly selected to further compare potential changes in selected plasma biomarker levels post-pregnancy (see Results).

Immunological assays

Samples were processed as described [19]. Briefly, whole blood samples were kept at room temperature during transport and prior to processing later that day. Whole blood plasma was collected from 10 mL sodium heparin Vacutainer tubes (BD, Mississauga, Canada) by centrifugation at 500g for 10 minutes, aliquoted and stored at -20°C. Immediately prior to use in immunological assays, thoroughly mixed plasma was subjected to a quick spin (500g, 1 minute) to remove protein/lipid precipitate. Samples for pregnant and one year postpartum, or one and three years postpartum, were analyzed as pairs on the same assay plates.

Meso Scale Discovery (MSD, Rockville, Maryland) singleplex assays were used to quantify analyte concentrations following the manufacturer`s instructions. Catalog numbers for the reagent kits used are provided at Table 2.

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Table 2. Catalog numbers for Meso Scale Discovery kits used in this publication.

https://doi.org/10.1371/journal.pone.0177813.t002

For all assays, concentrations were determined based on standard curves created using serial dilutions of fresh aliquots of constant recombinant lab standards prepared in culture medium and stored at -80°C in individual 400 uL aliquots (Cedarlane, Burlington, Canada; PeproTech, Quebec, Canada; R&D Systems, Minneapolis, Minnesota). Longitudinal sample sets from each individual were always paired on the same assay plates. Median intra-assay variation was typically below 5%.

Statistics

Group results are presented as medians, with each point representing the average (mean) value obtained from duplicate or triplicate analyses of an individual woman’s plasma at that timepoint. Supporting information S1 File contains the raw duplicates or triplicates used to calculate the mean values for each cytokine or chemokine, for each woman, at each visit, under each condition examined, that were then used to create the figures presented. Data for each population were analyzed using GraphPad Prism (La Jolla, California). Pairwise comparisons (Wilcoxon Matched Pairs/Signed Rank tests) were used for most data sets. The Spearman rank order correlation coefficient (non-parametric) was used to assess potential associations between plasma biomarker levels and increasing gestational age. Differences were considered significant at the 95% confidence level (two-tailed p<0.05).

Results

Alterations in basal innate immune balance are characteristic of healthy human pregnancy

This longitudinal study aimed to determine whether the constitutive immune status of healthy pregnant women exhibits a pro- or anti-inflammatory bias and whether it changes during pregnancy. As described in detail at Material and Methods, plasma samples were obtained at a single time point during pregnancy, again one year postpartum, and for a randomly obtained subset of individuals who did not experience further pregnancies in the interim, at three years postpartum. Two representative biomarkers of pro- and anti-inflammatory responses were assessed initially (Fig 1). Pro-inflammatory chemokine CCL2 was readily detectible in all individuals. Among the 251 women examined, systemic CCL2 was found to be reduced by 40% during pregnancy compared to levels one year postpartum (p<0.0001, Wilcoxon matched pairs, medians 110 vs. 154 pg/mL). Conversely, sTNF-RI was 38% elevated during pregnancy (medians 1,266 vs. 913, p<0.0001). Thus, the median ratio of these anti-inflammatory:pro-inflammatory innate biomarkers (sTNF-RI:CCL2) changed from 11.4 during pregnancy to 5.9 a year following delivery. This suggests that constitutive maternal status may incline towards an anti-inflammatory balance over the course of pregnancy.

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Fig 1. Among healthy women, a systemic bias towards a resting anti-inflammatory phenotype is evident in vivo during pregnancy.

Paired plasma samples from 251 women are assessed during and one year following healthy pregnancy. Data are presented as pg/mL. Bars represent median values of each data set. Wilcoxon paired analyses are shown.

https://doi.org/10.1371/journal.pone.0177813.g001

Given the large number of pro- and anti-inflammatory cytokines and inhibitors involved in human immune regulation, this analysis was extended in approximately every second woman (n = 120) to a panel of five additional pro-inflammatory biomarkers (CXCL10, TNFα, IL-18, IL-6 and CXCL8) as well as three more anti-inflammatory biomarkers (IL-10, sTNF-RII and IL-1Ra). The cytokines selected were chosen on the basis of being (i) routinely present in the plasma of healthy humans and (ii) having been extensively implicated in immune regulation of inflammation in murine and human studies. These large panels of biomarkers were used in preference to relying upon a single biomarker (CRP or IL-6 or IL-10, as is commonly done) in order to strengthen the capacity to draw conclusions about pro- vs. anti- inflammatory bias in vivo during pregnancy. A brief overview of the major cellular sources and biological functions of the cytokines, chemokines and receptors studied is provided in Table 3.

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Table 3. Cytokine, chemokine and soluble receptor biomarkers examined in this publication.

https://doi.org/10.1371/journal.pone.0177813.t003

Fig 2 demonstrates that during healthy pregnancy, most pro-inflammatory cytokines were indeed reduced relative to levels in the same women one year postpartum. Thus, constitutive CXCL10, TNFα and IL-18 were reduced during pregnancy. Median IL-6 trended lower by 42%, but the difference did not reach statistical significance. There was no evidence of changes in constitutive CXCL8 levels during healthy pregnancy. Note that due to the inherent immunological diversity characteristic of human populations, and to avoid compression of clearly positive but low levels of cytokine expression in some individuals, y-axis breaks are included.

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Fig 2. Basal levels of multiple pro-inflammatory innate biomarkers are reduced in vivo during healthy pregnancy.

n = 120 longitudinal sample pairs. Bars represent median values of each data set. Wilcoxon paired analyses are shown.

https://doi.org/10.1371/journal.pone.0177813.g002

Anti-inflammatory biomarkers (sTNF-RI, sTNF-RII, and IL-1Ra) demonstrated that unlike the reductions seen in constitutive pro-inflammatory cytokine expression, anti-inflammatory biomarker levels were elevated during pregnancy (Figs 1 and 3, p<0.0001). Interestingly, plasma IL-10, readily quantified in ~85% of the population, did not differ. Taken together, the data suggest that healthy pregnancy is characterized by transiently decreased pro-, and increased anti-inflammatory expression. This self-resolves by one year postpartum.

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Fig 3. Constitutive expression of multiple anti-inflammatory biomarkers is increased during pregnancy.

n = 120 longitudinal sample pairs. Bars represent median values of each data set. Wilcoxon paired analyses are shown.

https://doi.org/10.1371/journal.pone.0177813.g003

Validity of one year postpartum as a surrogate for the non-pregnant state

It is not logistically feasible to recruit women one year prior to an anticipated conception in order to assess their then basal systemic immune status. We therefore addressed the possibility that one year postpartum does not allow sufficient time for the innate immune system to return to the non-pregnant status, hence is not an appropriate comparison group. 32 randomly selected women who remained non-pregnant over the two years following the one year postpartum visit were examined. At this year three visit, plasma samples were obtained and compared (at the same time, in parallel assays) with plasma obtained from the same women at one year postpartum. One pro- and one anti-inflammatory biomarker that had exhibited differential expression during pregnancy (CCL2 and IL-1Ra) and one pro- and one anti-inflammatory biomarker that had been unchanged during pregnancy (CXCL8 and IL-10) were examined. Fig 4 demonstrates that the level of each cytokine was stable within an individual at one and three years post-pregnancy. This supports the concept that one (or three) year postpartum samples offer an appropriately stable comparator for non-pregnant status in this longitudinal study.

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Fig 4. Stability of in vivo pro- and anti-inflammatory plasma biomarkers.

n = 32 longitudinal sample pairs. Wilcoxon paired analyses are shown.

https://doi.org/10.1371/journal.pone.0177813.g004

Anti-inflammatory bias is evident at least as early as the second trimester

The comparisons above test the hypothesis that resting constitutive innate immune status is distinct during healthy pregnancy. To better understand the kinetics of this shift in resting immune status, the population was next stratified by trimester of recruitment. With only a small number of women recruited during the first trimester, analysis centred on the second and third trimesters. Fig 5 demonstrates basal (i.e. healthy, resting) innate immune status is skewed towards an anti-inflammatory phenotype at least as early as the second trimester.

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Fig 5. Longitudinal analysis of differences in pro- and anti-inflammatory cytokines in second and third trimesters.

Independent panels of volunteers were examined during the second or third trimester and compared with levels one year postpartum. Bars represent median values of each data set. Wilcoxon paired analyses are shown.

https://doi.org/10.1371/journal.pone.0177813.g005

The intensity of anti-inflammatory bias increases with increasing gestational age

Finally, to determine if the intensity of anti-inflammatory phenotypic changes are altered with the progression of pregnancy, we assessed relationships between plasma biomarker concentrations and gestational age. sTNF-RI, IL-1Ra (Fig 6) and sTNF-RII (not shown) all exhibited increasingly intense in vivo expression with increased gestational age. Conversely, the decrease in pro-inflammatory cytokine expression (Fig 6: CCL2 and IL-18; data not shown: CXCL8, CXCL10, IL-6 and TNFα) was constant and exhibited no relationship with increasing gestational age. Thus, the shift towards an increasingly anti-inflammatory bias intensified with increasing gestational age during healthy pregnancy.

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Fig 6. Relationships between gestational age and intensity of anti-inflammatory or pro-inflammatory plasma biomarker expression.

Spearman regression analyses are shown.

https://doi.org/10.1371/journal.pone.0177813.g006

Discussion

Although most pregnancies lead to healthy infants, prior research has focused heavily on diseases of pregnancy. Here, maternal health was examined in 251 healthy pregnant women over up to three years. The data reveal that at least as early as the second trimester, women exhibit increasingly strong constitutive expression of anti-inflammatory mediators and reduced expression of many, but not all, cytokines linked to host defense and inflammatory immune capacity. This transient anti-inflammatory phenotype intensifies with increasing gestational age and is self-resolving by one year postpartum.

Our primary focus here is maternal health and the systemic, constitutive innate immune status exhibited by women during pregnancy. This is not an investigation of factors which enable pregnancy to become established, to proceed to term, or to respond to acute viral or bacterial infection. There is a longstanding lack of agreement regarding constitutive innate immune status during a healthy pregnancy. Small cohorts of healthy pregnant women are incorporated in most studies that examine diseases of pregnancy. In those studies, cross-sectional comparisons are drawn with a broad range of difficult pregnancies, rather than explicitly using well-powered longitudinal study designs to examine the status of healthy women during vs. post-pregnancy. Not surprisingly, such studies do not provide a clear consensus. One school argues that systemic immune status in vivo, unlike immune status at the maternal/fetal interface, reflects a generalized mild inflammatory response [7073]. Others argue for the dominance of anti-inflammatory responses [74, 75]. These apparent contradictions may be due to cross-sectional study designs, cohorts of relatively small size, the resulting impact of subject to subject variability, and reliance on a small number of biomarkers (often one) to assess innate immune bias in vivo. For example, two of the largest longitudinal studies available [76, 77] are composed of 48 and 21 healthy women respectively who are followed through pregnancy and postpartum. Many studies involve different ethnicities: Kraus included a 94% Hispanic/Black population [76], while Szarka utilized a Caucasian population [78]. As pointed out more than two decades ago [79], due to high inter-subject variability inherent to any outbred population, a longitudinal, matched study design involving a large n is logistically challenging, but highly important.

This research has important caveats. Firstly, because a longitudinal, multi-year study design was selected to achieve increased sensitivity, it was not socially or logistically feasible to recruit individuals prior to an anticipated pregnancy. For this reason, pregnant women were compared with their immune status at one year and, for a subset, three years postpartum. Pre-pregnancy immune status could not be directly determined. Secondly, a potential confounder that cannot be ruled out is the impact of specific environmental antigens and pathogens on these findings. Women with complicated pregnancies with known linkages to altered innate immunity (i.e. preeclampsia) are excluded from this study. Among the women studied, clinical assessments at each blood draw excluded women with active transient URT or GI infections. The data reported above, characterizing the constitutive in vivo phenotype of healthy normal pregnancy positions us to better assess the impact of environmental and genetic influences in pregnancy in subsequent studies. A third caveat is that the impact of menstrual stage postpartum at sampling could influence some values obtained. This underlines the need for sufficient power because the impact of such variables is increasingly reduced as the number of individuals examined increases.

A potential confounder to interpretation of the data obtained was day-to-day stability of biomarker expression within a given individual. We found this to have minimal impact because, as shown in Fig 4, and as was previously reported in short-term studies conducted in men and non-pregnant women [76, 80], systemic levels of most biomarkers are remarkably stable across time (days-weeks) in healthy individuals.

The immunological and clinical implications that result from the increasingly pronounced anti-inflammatory phenotype that developed over the course of healthy pregnancy remains speculative. Extensive literature demonstrates associations between pro-inflammatory or type 1 cytokines and recurrent spontaneous miscarriage or preterm delivery. Exogenous TNFα and IFN inhibit the outgrowth of human trophoblasts in vitro and induce apoptosis of human villous trophoblast cells. Murine studies demonstrate that administration of pro-inflammatory cytokines (i.e. TNFα, IFN, IL-2) into pregnant mice causes increased abortion. Conversely, administration of IL-10 prevents fetal wastage in abortion-prone mice [81, 82]. Thus, there is consensus that controls on excessive pro-inflammatory innate responses are essential for successful pregnancy [75].

These data may stand in contrast to in vivo expression of acute phase proteins during healthy pregnancy. Multiple studies have found increased plasma/serum CRP levels vs. non-pregnant controls [8386]. The extent to which changes in this largely IL-6 and TNFα driven biomarker of inflammation are due to activation of classical innate immune responses or other cells (i.e. adipocytes or necrotic processes associated with placenta ageing) is under active investigation [83, 87, 88]. Interestingly, several groups have found undetectable changes or decreases in CRP over the course of healthy pregnancy [83, 8992]. This inconsistency, and the many pregnancy independent factors (i.e. obesity) that can influence CRP levels, underlines a need for caution and continued research prior to drawing mechanistic conclusions about the role any of these mediators play in successful conclusion of pregnancy.

In this study, we do not address putative differences in maternal immune responses upon infection in vivo or acute in vitro activation. Studies examining in vitro responses to various pattern recognition receptor (PRR) ligands are currently underway as a complementary approach to understanding changes in maternal health that can occur during pregnancy.

With increasing attention given to defining what constitutes a healthy pregnancy [93], this study provides valuable insight into systemic innate immune changes that result in expression of an increasingly intense anti-inflammatory phenotype in vivo during pregnancy. It underlines the need for further characterization of what constitutes a successful environment for healthy human pregnancy.

Supporting information

S1 File. Raw duplicates and triplicates from immunological assays performed.

https://doi.org/10.1371/journal.pone.0177813.s001

(XLSX)

Acknowledgments

We are grateful to all the families who took part in this study and the entire CHILD research team. We also thank Saiful Huq for database assistance and Paul Lopez for editorial assistance. CHILD (Canadian Healthy Infant Longitudinal Development Study, headquartered at McMaster University, Hamilton, Canada) investigators include: MR Sears (Director), McMaster University; P Subbarao (co-Director), The Hospital for Sick Children; R Allen, Simon Fraser University; SS Anand, McMaster University; AB Becker, University of Manitoba; AD Befus, University of Alberta; M Brauer, University of British Columbia; JR Brook, University of Toronto; E Chen, Northwestern University, Chicago; M Cyr, McMaster University; D Daley, University of British Columbia; S Dell, Sick Children’s Hospital; JA Denburg, McMaster University; S Elliott, University of Waterloo; H Grasemann, Sick Children’s Hospital; K HayGlass, University of Manitoba; R Hegele, Sick Children’s Hospital; DL Holness, University of Toronto; WYW Lou, University of Toronto; MS Kobor, University of British Columbia; TR Kollman, University of British Columbia; AL Kozyrskyj, University of Alberta; C Laprise, Universite du Quebec a Chicoutimi; M Larche, McMaster University; J Macri, McMaster University; PM Mandhane, University of Alberta; G Miller, Northwestern University, Chicago; R Moqbel (deceased), University of Manitoba; T Moraes, Sick Children’s Hospital; PD Pare, University of British Columbia; C Ramsey, University of Manitoba; F Ratjen, Sick Children’s Hospital; A Sandford, University of British Columbia; JA Scott, University of Toronto; J Scott, University of Toronto; F Silverman, University of Toronto; T Takaro, Simon Fraser University; P Tang, University of British Columbia; S Tebbutt, University of British Columbia; T To, Sick Children’s Hospital; SE Turvey, University of British Columbia, all in Canada.

Author Contributions

  1. Conceptualization: KTH ABB CG RC.
  2. Data curation: CG RC KTH MRS.
  3. Formal analysis: KTH CG ABB RC.
  4. Funding acquisition: MRS ABB KTH SET PS PJM.
  5. Investigation: KTH ABB CG RC WPS.
  6. Methodology: CG RC WPS ABB MRS SET PJM PS KTH.
  7. Project administration: KTH ABB RC MRS.
  8. Resources: CG RC WPS ABB MRS SET PJM PS KTH.
  9. Supervision: KTH ABB MRS.
  10. Validation: KTH ABB CG RC WPS.
  11. Visualization: CG WPS.
  12. Writing – original draft: KTH CG.
  13. Writing – review & editing: CG RC WPS ABB MRS SET PJM PS KTH CHILD.

References

  1. 1. Chaouat G, Tranchot Diallo J, Volumenie JL, Menu E, Gras G, Delage G, et al. Immune suppression and Th1/Th2 balance in pregnancy revisited: a (very) personal tribute to Tom Wegmann. Am J Reprod Immunol. 1997 Jun;37(6):427–34. pmid:9228297
  2. 2. St Louis D, Romero R, Plazyo O, Arenas-Hernandez M, Panaitescu B, Xu Y, et al. Invariant NKT Cell Activation Induces Late Preterm Birth That Is Attenuated by Rosiglitazone. J Immunol. 2016 Feb 01;196(3):1044–59. pmid:26740111
  3. 3. PrabhuDas M, Bonney E, Caron K, Dey S, Erlebacher A, Fazleabas A, et al. Immune mechanisms at the maternal-fetal interface: perspectives and challenges. Nat Immunol. 2015 Apr;16(4):328–34. pmid:25789673
  4. 4. Svensson-Arvelund J, Mehta RB, Lindau R, Mirrasekhian E, Rodriguez-Martinez H, Berg G, et al. The human fetal placenta promotes tolerance against the semiallogeneic fetus by inducing regulatory T cells and homeostatic M2 macrophages. J Immunol. 2015 Feb 15;194(4):1534–44. pmid:25560409
  5. 5. Baylis F. Pregnant women deserve better. Nature. 2010 Jun 10;465(7299):689–90. pmid:20535185
  6. 6. Catalano PW, MA. Wise, PH. Bianchi, DW. Saade, GR. Scientific Vision Workshop on Pregnancy and Pregnancy Outcomes. Bethesa, Maryland2011 [updated 2011; cited 2016 02/18/2016]; https://www.nichd.nih.gov/vision/vision_themes/pregnancy/Documents/Vision_Pregnancy_WP_042811.pdf.
  7. 7. Foulkes MA, Grady C, Spong CY, Bates A, Clayton JA. Clinical research enrolling pregnant women: a workshop summary. J Womens Health (Larchmt). 2011 Oct;20(10):1429–32.
  8. 8. Heyborne KS, R M. Reproductive Immunology. Bronson RA, N J. Anderson D. Branch DW. Kutteh WH., editor. Cambridge: Blackwell Science; 1996.
  9. 9. Huang E, Wells CA. The ground state of innate immune responsiveness is determined at the interface of genetic, epigenetic, and environmental influences. J Immunol. 2014 Jul 1;193(1):13–9. pmid:24951823
  10. 10. Gonzalez-Perez G, Hicks AL, Tekieli TM, Radens CM, Williams BL, Lamouse-Smith ES. Maternal Antibiotic Treatment Impacts Development of the Neonatal Intestinal Microbiome and Antiviral Immunity. J Immunol. 2016 May 01;196(9):3768–79. pmid:27036912
  11. 11. Mendola P, Wallace M, Hwang BS, Liu D, Robledo C, Mannisto T, et al. Preterm birth and air pollution: Critical windows of exposure for women with asthma. J Allergy Clin Immunol. 2016 Aug;138(2):432–40 e5. pmid:26944405
  12. 12. von Mutius E, Martinez FD. Inconclusive Results of Randomized Trials of Prenatal Vitamin D for Asthma Prevention in Offspring: Curbing the Enthusiasm. JAMA. 2016 Jan 26;315(4):347–8. pmid:26813205
  13. 13. Tyrrell J, Richmond RC, Palmer TM, Feenstra B, Rangarajan J, Metrustry S, et al. Genetic Evidence for Causal Relationships Between Maternal Obesity-Related Traits and Birth Weight. JAMA. 2016 Mar 15;315(11):1129–40. pmid:26978208
  14. 14. Aagaard-Tillery KM, Silver R, Dalton J. Immunology of normal pregnancy. Semin Fetal Neonatal Med. 2006 Oct;11(5):279–95. pmid:16784908
  15. 15. Visser N, van Rijn BB, Rijkers GT, Franx A, Bruinse HW. Inflammatory changes in preeclampsia: current understanding of the maternal innate and adaptive immune response. Obstet Gynecol Surv. 2007 Mar;62(3):191–201. pmid:17306041
  16. 16. Aye IL, Lager S, Ramirez VI, Gaccioli F, Dudley DJ, Jansson T, et al. Increasing maternal body mass index is associated with systemic inflammation in the mother and the activation of distinct placental inflammatory pathways. Biol Reprod. 2014 Jun;90(6):129. pmid:24759787
  17. 17. Chawes BL, Stokholm J, Bonnelykke K, Brix S, Bisgaard H. Neonates with reduced neonatal lung function have systemic low-grade inflammation. J Allergy Clin Immunol. 2015 Jun;135(6):1450–6 e1. pmid:25579483
  18. 18. Subbarao P, Anand SS, Becker AB, Befus AD, Brauer M, Brook JR, et al. The Canadian Healthy Infant Longitudinal Development (CHILD) Study: examining developmental origins of allergy and asthma. Thorax. 2015 Oct;70(10):998–1000. pmid:26069286
  19. 19. Moraes TJ, Lefebvre DL, Chooniedass R, Becker AB, Brook JR, Denburg J, et al. The Canadian healthy infant longitudinal development birth cohort study: biological samples and biobanking. Paediatr Perinat Epidemiol. 2015 Jan;29(1):84–92. pmid:25405552
  20. 20. Pendeloski KP, Ono E, Torloni MR, Mattar R, Daher S. Maternal obesity and inflammatory mediators: A controversial association. Am J Reprod Immunol. 2017 Mar 22;
  21. 21. Carr MW, Roth SJ, Luther E, Rose SS, Springer TA. Monocyte chemoattractant protein 1 acts as a T-lymphocyte chemoattractant. Proc Natl Acad Sci U S A. 1994 Apr 26;91(9):3652–6. pmid:8170963
  22. 22. Xu LL, Warren MK, Rose WL, Gong W, Wang JM. Human recombinant monocyte chemotactic protein and other C-C chemokines bind and induce directional migration of dendritic cells in vitro. J Leukoc Biol. 1996 Sep;60(3):365–71. pmid:8830793
  23. 23. Lam VC, Lanier LL. NK cells in host responses to viral infections. Curr Opin Immunol. 2016 Dec 13;4443–51.
  24. 24. Xia M, Sui Z. Recent developments in CCR2 antagonists. Expert Opin Ther Pat. 2009 Mar;19(3):295–303. pmid:19441905
  25. 25. O'Connor T, Borsig L, Heikenwalder M. CCL2-CCR2 Signaling in Disease Pathogenesis. Endocr Metab Immune Disord Drug Targets. 2015 15(2):105–18. pmid:25772168
  26. 26. Hedges JC, Singer CA, Gerthoffer WT. Mitogen-activated protein kinases regulate cytokine gene expression in human airway myocytes. Am J Respir Cell Mol Biol. 2000 Jul;23(1):86–94. pmid:10873157
  27. 27. Harada A, Sekido N, Akahoshi T, Wada T, Mukaida N, Matsushima K. Essential involvement of interleukin-8 (IL-8) in acute inflammation. J Leukoc Biol. 1994 Nov;56(5):559–64. pmid:7964163
  28. 28. Baggiolini M, Walz A, Kunkel SL. Neutrophil-activating peptide-1/interleukin 8, a novel cytokine that activates neutrophils. J Clin Invest. 1989 Oct;84(4):1045–9. pmid:2677047
  29. 29. Hosoki K, Itazawa T, Boldogh I, Sur S. Neutrophil recruitment by allergens contribute to allergic sensitization and allergic inflammation. Curr Opin Allergy Clin Immunol. 2016 Feb;16(1):45–50. pmid:26694038
  30. 30. Tan SY, Weninger W. Neutrophil migration in inflammation: intercellular signal relay and crosstalk. Curr Opin Immunol. 2016 Dec 09;4434–42.
  31. 31. Luster AD, Unkeless JC, Ravetch JV. Gamma-interferon transcriptionally regulates an early-response gene containing homology to platelet proteins. Nature. 1985 Jun 20–26;315(6021):672–6. pmid:3925348
  32. 32. Dufour JH, Dziejman M, Liu MT, Leung JH, Lane TE, Luster AD. IFN-gamma-inducible protein 10 (IP-10; CXCL10)-deficient mice reveal a role for IP-10 in effector T cell generation and trafficking. J Immunol. 2002 Apr 01;168(7):3195–204. pmid:11907072
  33. 33. Angiolillo AL, Sgadari C, Taub DD, Liao F, Farber JM, Maheshwari S, et al. Human interferon-inducible protein 10 is a potent inhibitor of angiogenesis in vivo. J Exp Med. 1995 Jul 01;182(1):155–62. pmid:7540647
  34. 34. Campbell JD, Gangur V, Simons FE, HayGlass KT. Allergic humans are hyporesponsive to a CXCR3 ligand-mediated Th1 immunity-promoting loop. FASEB J. 2004 Feb;18(2):329–31. pmid:14657006
  35. 35. Hamidzadeh K, Christensen SM, Dalby E, Chandrasekaran P, Mosser DM. Macrophages and the Recovery from Acute and Chronic Inflammation. Annu Rev Physiol. 2017 Feb 10;79567–92.
  36. 36. Hunter CA, Jones SA. IL-6 as a keystone cytokine in health and disease. Nat Immunol. 2015 May;16(5):448–57. pmid:25898198
  37. 37. van der Poll T, Keogh CV, Guirao X, Buurman WA, Kopf M, Lowry SF. Interleukin-6 gene-deficient mice show impaired defense against pneumococcal pneumonia. J Infect Dis. 1997 Aug;176(2):439–44. pmid:9237710
  38. 38. Kristiansen OP, Mandrup-Poulsen T. Interleukin-6 and diabetes: the good, the bad, or the indifferent? Diabetes. 2005 Dec;54 Suppl 2S114–24.
  39. 39. Dubinski A, Zdrojewicz Z. [The role of interleukin-6 in development and progression of atherosclerosis]. Pol Merkur Lekarski. 2007 Apr;22(130):291–4. pmid:17684929
  40. 40. Dowlati Y, Herrmann N, Swardfager W, Liu H, Sham L, Reim EK, et al. A meta-analysis of cytokines in major depression. Biol Psychiatry. 2010 Mar 01;67(5):446–57. pmid:20015486
  41. 41. Swardfager W, Lanctot K, Rothenburg L, Wong A, Cappell J, Herrmann N. A meta-analysis of cytokines in Alzheimer's disease. Biol Psychiatry. 2010 Nov 15;68(10):930–41. pmid:20692646
  42. 42. Tackey E, Lipsky PE, Illei GG. Rationale for interleukin-6 blockade in systemic lupus erythematosus. Lupus. 2004 13(5):339–43. pmid:15230289
  43. 43. Gado K, Domjan G, Hegyesi H, Falus A. Role of INTERLEUKIN-6 in the pathogenesis of multiple myeloma. Cell Biol Int. 2000 24(4):195–209. pmid:10816321
  44. 44. Smith PC, Hobisch A, Lin DL, Culig Z, Keller ET. Interleukin-6 and prostate cancer progression. Cytokine Growth Factor Rev. 2001 Mar;12(1):33–40. pmid:11312117
  45. 45. Nishimoto N. Interleukin-6 in rheumatoid arthritis. Curr Opin Rheumatol. 2006 May;18(3):277–81. pmid:16582692
  46. 46. Banchereau J, Pascual V, O'Garra A. From IL-2 to IL-37: the expanding spectrum of anti-inflammatory cytokines. Nat Immunol. 2012 Oct;13(10):925–31. pmid:22990890
  47. 47. Gabrysova L, Howes A, Saraiva M, O'Garra A. The regulation of IL-10 expression. Curr Top Microbiol Immunol. 2014 380157–90.
  48. 48. Mosser DM, Zhang X. Interleukin-10: new perspectives on an old cytokine. Immunol Rev. 2008 Dec;226205–18.
  49. 49. Pestka S, Krause CD, Sarkar D, Walter MR, Shi Y, Fisher PB. Interleukin-10 and related cytokines and receptors. Annu Rev Immunol. 2004 22929–79.
  50. 50. Saraiva M, O'Garra A. The regulation of IL-10 production by immune cells. Nat Rev Immunol. 2010 Mar;10(3):170–81. pmid:20154735
  51. 51. de Waal Malefyt R, Abrams J, Bennett B, Figdor CG, de Vries JE. Interleukin 10(IL-10) inhibits cytokine synthesis by human monocytes: an autoregulatory role of IL-10 produced by monocytes. J Exp Med. 1991 Nov 01;174(5):1209–20. pmid:1940799
  52. 52. Moore KW, de Waal Malefyt R, Coffman RL, O'Garra A. Interleukin-10 and the interleukin-10 receptor. Annu Rev Immunol. 2001 19683–765.
  53. 53. Dinarello CA, Novick D, Kim S, Kaplanski G. Interleukin-18 and IL-18 binding protein. Front Immunol. 2013 Oct 08;4289.
  54. 54. Banchereau R, Cepika AM, Banchereau J, Pascual V. Understanding Human Autoimmunity and Autoinflammation Through Transcriptomics. Annu Rev Immunol. 2017 Jan 30;
  55. 55. Sutinen EM, Pirttila T, Anderson G, Salminen A, Ojala JO. Pro-inflammatory interleukin-18 increases Alzheimer's disease-associated amyloid-beta production in human neuron-like cells. J Neuroinflammation. 2012 Aug 16;9199.
  56. 56. Okamura H, Tsutsi H, Komatsu T, Yutsudo M, Hakura A, Tanimoto T, et al. Cloning of a new cytokine that induces IFN-gamma production by T cells. Nature. 1995 Nov 02;378(6552):88–91. pmid:7477296
  57. 57. Liu Z, Wang H, Xiao W, Wang C, Liu G, Hong T. Thyrocyte interleukin-18 expression is up-regulated by interferon-gamma and may contribute to thyroid destruction in Hashimoto's thyroiditis. Int J Exp Pathol. 2010 Oct;91(5):420–5. pmid:20586818
  58. 58. Perrier S, Darakhshan F, Hajduch E. IL-1 receptor antagonist in metabolic diseases: Dr Jekyll or Mr Hyde? FEBS Lett. 2006 Nov 27;580(27):6289–94. pmid:17097645
  59. 59. Di Paolo NC, Shayakhmetov DM. Interleukin 1alpha and the inflammatory process. Nat Immunol. 2016 Jul 19;17(8):906–13. pmid:27434011
  60. 60. Ito Y, Kaneko N, Iwasaki T, Morikawa S, Kaneko K, Masumoto J. IL-1 as a target in inflammation. Endocr Metab Immune Disord Drug Targets. 2015 15(3):206–11. pmid:26333726
  61. 61. Dinarello CA. The interleukin-1 family: 10 years of discovery. FASEB J. 1994 Dec;8(15):1314–25. pmid:8001745
  62. 62. El-Omar EM, Carrington M, Chow WH, McColl KE, Bream JH, Young HA, et al. Interleukin-1 polymorphisms associated with increased risk of gastric cancer. Nature. 2000 Mar 23;404(6776):398–402. pmid:10746728
  63. 63. Aksentijevich I, Masters SL, Ferguson PJ, Dancey P, Frenkel J, van Royen-Kerkhoff A, et al. An autoinflammatory disease with deficiency of the interleukin-1-receptor antagonist. N Engl J Med. 2009 Jun 04;360(23):2426–37. pmid:19494218
  64. 64. Willrich MA, Murray DL, Snyder MR. Tumor necrosis factor inhibitors: clinical utility in autoimmune diseases. Transl Res. 2015 Feb;165(2):270–82. pmid:25305470
  65. 65. Ware CF, Santee S, Glass A. Tumor necrosis factor-related ligands and receptors. In: Thomson A, editor. The Cytokine Handbook. Third ed. San Diego, CA: Academic Press; 1998. p. 549–92.
  66. 66. Wei M, Kuukasjarvi P, Laurikka J, Pehkonen E, Kaukinen S, Laine S, et al. Inflammatory cytokines and soluble receptors after coronary artery bypass grafting. Cytokine. 2001 Aug 21;15(4):223–8. pmid:11563882
  67. 67. Locksley RM, Killeen N, Lenardo MJ. The TNF and TNF receptor superfamilies: integrating mammalian biology. Cell. 2001 Feb 23;104(4):487–501. pmid:11239407
  68. 68. Baxter AE, Kaufmann DE. Tumor-necrosis factor is a master of T cell exhaustion. Nat Immunol. 2016 May;17(5):476–8. pmid:27092797
  69. 69. Green WD, Beck MA. Obesity altered T cell metabolism and the response to infection. Curr Opin Immunol. 2017 Mar 27;461–7.
  70. 70. Challis JR, Lockwood CJ, Myatt L, Norman JE, Strauss JF 3rd, Petraglia F. Inflammation and pregnancy. Reprod Sci. 2009 Feb;16(2):206–15. pmid:19208789
  71. 71. Sacks G, Sargent I, Redman C. An innate view of human pregnancy. Immunol Today. 1999 Mar;20(3):114–8. pmid:10203701
  72. 72. Sacks GP, Studena K, Sargent K, Redman CW. Normal pregnancy and preeclampsia both produce inflammatory changes in peripheral blood leukocytes akin to those of sepsis. Am J Obstet Gynecol. 1998 Jul;179(1):80–6. pmid:9704769
  73. 73. Blank V, Hirsch E, Challis JR, Romero R, Lye SJ. Cytokine signaling, inflammation, innate immunity and preterm labour—a workshop report. Placenta. 2008 Mar;29 Suppl AS102–4.
  74. 74. Munn DH, Zhou M, Attwood JT, Bondarev I, Conway SJ, Marshall B, et al. Prevention of allogeneic fetal rejection by tryptophan catabolism. Science. 1998 Aug 21;281(5380):1191–3. pmid:9712583
  75. 75. Chatterjee P, Chiasson VL, Bounds KR, Mitchell BM. Regulation of the Anti-Inflammatory Cytokines Interleukin-4 and Interleukin-10 during Pregnancy. Front Immunol. 2014 5253.
  76. 76. Kraus TA, Sperling RS, Engel SM, Lo Y, Kellerman L, Singh T, et al. Peripheral blood cytokine profiling during pregnancy and post-partum periods. Am J Reprod Immunol. 2010 Dec;64(6):411–26. pmid:20712812
  77. 77. Bjorkander S, Bremme K, Persson JO, van Vollenhoven RF, Sverremark-Ekstrom E, Holmlund U. Pregnancy-associated inflammatory markers are elevated in pregnant women with systemic lupus erythematosus. Cytokine. 2012 Aug;59(2):392–9. pmid:22633082
  78. 78. Szarka A, Rigo J Jr., Lazar L, Beko G, Molvarec A. Circulating cytokines, chemokines and adhesion molecules in normal pregnancy and preeclampsia determined by multiplex suspension array. BMC Immunol. 2010 1159.
  79. 79. Johnstone FD, Thong KJ, Bird AG, Whitelaw J. Lymphocyte subpopulations in early human pregnancy. Obstet Gynecol. 1994 Jun;83(6):941–6. pmid:8190436
  80. 80. Campbell JD, Stinson MJ, Simons FE, Rector ES, HayGlass KT. In vivo stability of human chemokine and chemokine receptor expression. Hum Immunol. 2001 Jul;62(7):668–78. pmid:11423172
  81. 81. Chaouat G, Assal Meliani A, Martal J, Raghupathy R, Elliott JF, Mosmann T, et al. IL-10 prevents naturally occurring fetal loss in the CBA x DBA/2 mating combination, and local defect in IL-10 production in this abortion-prone combination is corrected by in vivo injection of IFN-tau. J Immunol. 1995 May 01;154(9):4261–8. pmid:7722286
  82. 82. Thaxton JE, Sharma S. Interleukin-10: a multi-faceted agent of pregnancy. Am J Reprod Immunol. 2010 Jun;63(6):482–91. pmid:20163400
  83. 83. Belo L, Santos-Silva A, Rocha S, Caslake M, Cooney J, Pereira-Leite L, et al. Fluctuations in C-reactive protein concentration and neutrophil activation during normal human pregnancy. Eur J Obstet Gynecol Reprod Biol. 2005 Nov 01;123(1):46–51. pmid:16260340
  84. 84. Miller EM. Changes in serum immunity during pregnancy. Am J Hum Biol. 2009 May-Jun;21(3):401–3. pmid:19189417
  85. 85. Perucci LO, Carneiro FS, Ferreira CN, Sugimoto MA, Soriani FM, Martins GG, et al. Annexin A1 Is Increased in the Plasma of Preeclamptic Women. PLoS One. 2015 10(9):e0138475. pmid:26398190
  86. 86. McDade TW, Borja JB, Largado F, Adair LS, Kuzawa CW. Adiposity and Chronic Inflammation in Young Women Predict Inflammation during Normal Pregnancy in the Philippines. J Nutr. 2016 Feb;146(2):353–7. pmid:26764318
  87. 87. Romem Y, Artal R. C-reactive protein in pregnancy and in the postpartum period. Am J Obstet Gynecol. 1985 Feb 01;151(3):380–3. pmid:3970105
  88. 88. Rebelo F, Schlussel MM, Vaz JS, Franco-Sena AB, Pinto TJ, Bastos FI, et al. C-reactive protein and later preeclampsia: systematic review and meta-analysis taking into account the weight status. J Hypertens. 2013 Jan;31(1):16–26. pmid:23188419
  89. 89. Christian LM, Porter K. Longitudinal changes in serum proinflammatory markers across pregnancy and postpartum: effects of maternal body mass index. Cytokine. 2014 Dec;70(2):134–40. pmid:25082648
  90. 90. Friis CM, Paasche Roland MC, Godang K, Ueland T, Tanbo T, Bollerslev J, et al. Adiposity-related inflammation: effects of pregnancy. Obesity (Silver Spring). 2013 Jan;21(1):E124–30.
  91. 91. Stewart FM, Freeman DJ, Ramsay JE, Greer IA, Caslake M, Ferrell WR. Longitudinal assessment of maternal endothelial function and markers of inflammation and placental function throughout pregnancy in lean and obese mothers. J Clin Endocrinol Metab. 2007 Mar;92(3):969–75. pmid:17192290
  92. 92. Simavli S, Derbent AU, Uysal S, Turhan NO. Hepcidin, iron status, and inflammation variables among healthy pregnant women in the Turkish population. J Matern Fetal Neonatal Med. 2014 Jan;27(1):75–9. pmid:23662610
  93. 93. NICHD. Pregnancy: For Researchers and Health Care Practitioners 2013; https://www.nichd.nih.gov/health/topics/pregnancy/resources/Pages/providers.aspx.