Microchimerism in autoimmune disease: more questions than answers?

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.

Pregnancy, cardiovascular health, and microchimerism

PURPOSE OF REVIEW

To provide an updated review of scientific literature concerning associations between pregnancy and cardiovascular health among women, and to discuss a possible impact of microchimerism on the association.

RECENT FINDINGS

In most studies, pregnancy and childbirth is associated with increased risk of cardiovascular disease in women. Some ascribe the association mainly to lifestyle, whereas others suggest that pregnancy itself negatively affects women's cardiovascular health. Pregnancy is a natural source of microchimerism, which in turn markedly affects female health. The only study published in the area surprisingly shows that among middle-aged women, male-origin microchimerism (MOM) is associated with half the risk of developing ischemic heart disease (IHD). No similar association is found between MOM and ischemic stroke.

SUMMARY

The sparse evidence published suggests reduced risk of developing IHD among MOM-positive women. Despite the association being biologically plausible, replication of the findings is warranted to support that this is not a chance finding.

TFOS Lifestyle: Impact of lifestyle challenges on the ocular surface

Many factors in the domains of mental, physical, and social health have been associated with various ocular surface diseases, with most of the focus centered on aspects of dry eye disease (DED). Regarding mental health factors, several cross-sectional studies have noted associations between depression and anxiety, and medications used to treat these disorders, and DED symptoms. Sleep disorders (both involving quality and quantity of sleep) have also been associated with DED symptoms. Under the domain of physical health, several factors have been linked to meibomian gland abnormalities, including obesity and face mask wear. Cross-sectional studies have also linked chronic pain conditions, specifically migraine, chronic pain syndrome and fibromyalgia, to DED, principally focusing on DED symptoms. A systematic review and meta-analysis reviewed available data and concluded that various chronic pain conditions increased the risk of DED (variably defined), with odds ratios ranging from 1.60 to 2.16. However, heterogeneity was noted, highlighting the need for additional studies examining the impact of chronic pain on DED signs and subtype (evaporative versus aqueous deficient). With respect to societal factors, tobacco use has been most closely linked to tear instability, cocaine to decreased corneal sensitivity, and alcohol to tear film disturbances and DED symptoms.

Molecular Mechanisms in Autoimmune Thyroid Disease

The most common cause of acquired thyroid dysfunction is autoimmune thyroid disease, which is an organ-specific autoimmune disease with two presentation phenotypes: hyperthyroidism (Graves-Basedow disease) and hypothyroidism (Hashimoto's thyroiditis). Hashimoto's thyroiditis is distinguished by the presence of autoantibodies against thyroid peroxidase and thyroglobulin. Meanwhile, autoantibodies against the TSH receptor have been found in Graves-Basedow disease. Numerous susceptibility genes, as well as epigenetic and environmental factors, contribute to the pathogenesis of both diseases. This review summarizes the most common genetic, epigenetic, and environmental mechanisms involved in autoimmune thyroid disease.

Perinatal mental illness and maternal autoimmune disease: A review of current evidence and avenues for future research

This review summarizes evidence on the association between perinatal mental illness and maternal autoimmune disease and identifies avenues for future research. Perinatal mental illness has several characteristics in common with autoimmune disease, including increased incidence in the early postpartum period, recurrence across pregnancies, evidence of elevated immune-mediated cytokines, and familial risk, as well as the general predominance of mental illness in females versus males. Several studies have demonstrated elevated risk of maternal autoimmune disease in women with perinatal mental illness, and of perinatal mental illness in those with autoimmune dysfunction, suggesting a bi-directional relationship. Further research is needed to elucidate the importance of the specific diagnosis, severity, and timing of perinatal mental illness and specific diagnosis of autoimmune disease, as well as the relative importance of perinatal versus non-perinatal mental illness. Such research could have implications for prevention, treatment, and follow-up of perinatal mental illness.

Maternal versus paternal living kidney transplant donation is associated with lower rejection in young pediatric recipients: A Collaborative Transplant Study report

BACKGROUND

Approximately 1700 children per year with end-stage kidney disease undergo kidney transplantation in Europe and the United States of America; 30%-50% are living donor kidney transplantations. There may be immunological differences between paternal and maternal donors due to transplacental exchange of cells between the mother and fetus during pregnancy leading to microchimerism. We investigated whether the outcome of living-related kidney transplantation in young children is different after maternal compared with paternal organ donation.

METHODS

Using the international Collaborative Transplant Study (CTS) database, we analyzed epidemiological data of 7247 children and adolescents aged <18 years who had received a kidney transplant from either mother or father. Risk of treated rejection episodes and death-censored graft failure were computed using the Kaplan-Meier method and multivariable Cox regression.

RESULTS

In the recipient age group 1-4 years, the rate of treated rejection episodes in recipients of kidneys from maternal donors (N = 195) during the first 2 years post-transplant was significantly lower (hazard ratio HR = 0.47, p = .004) than in patients receiving kidneys from paternal donors (N = 179). This association between donor sex and risk of treated rejections was not observed in children aged 5-9 years. The 5-year death-censored graft survival in children aged 1-4 years with a maternal or paternal donor was comparable.

CONCLUSIONS

Maternal kidney donation in young pediatric renal transplant recipients is associated with an approximately 50% lower rate of treated rejection than paternal kidney donation. Whether this phenomenon is due to maternal microchimerism-induced donor-specific hyporesponsiveness must be evaluated in prospective mechanistic studies.

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.

Impact of Male-Origin Microchimerism on Cardiovascular Disease in Women: A Prospective Cohort Study

Increasing parity is associated with an increased risk of ischemic heart disease (IHD) and stroke in women. This is probably attributable to biological responses of pregnancy. Male cells of presumed fetal origin are commonly present in women years after pregnancy-a phenomenon termed male-origin microchimerism (MOM). In this study, we investigated whether MOM was associated with risk of IHD and ischemic stroke in women. We evaluated the association between MOM and ischemic events in a cohort of 766 Danish women enrolled in the Diet, Cancer and Health cohort during 1993-1997 when aged 50-64 years. Of these women, 545 (71.2%) tested positive for MOM through targeting of the Y chromosome (DYS14 DNA sequence) in their blood. Multiple Cox regression models were used to calculate hazard ratios with 95% confidence intervals. We found that MOM was associated with a significantly reduced rate of IHD (hazard ratio = 0.44, 95% confidence interval: 0.23, 0.83) but not ischemic stroke (hazard ratio = 0.80, 95% confidence interval: 0.46, 1.41). Our findings show that microchimerism positivity is associated with a lower rate of later IHD development in women. Although the underlying mechanisms are presently unknown, MOM may be relevant in women's cardiovascular health. More studies are needed to confirm these findings.

Autoimmune thyroid disorders and rheumatoid arthritis: A bidirectional interplay

Rheumatoid arthritis (RA) and autoimmune thyroid disease (AITD) can occur in the same patient in the autoimmune polyglandular syndrome 2. The association of the two conditions has been recognized long-time ago and the prevalence of AITD in patients with RA and vice versa is well assessed. Geographical variation of AITD and related autoantibodies in RA patients is partly due to ethnic and environmental differences of the studied populations. The impacts of thyroid disorders on RA outcome and vice versa are still controversy. In both AITD and RA genetic susceptibility and environmental factors play a synergic role in the development of the diseases. In this review we aimed at investigating the association of AITD and thyroid autoantibodies with RA, the common pathogenic pathways, the correlation with RA disease activity, and influence of the treatment.

Exacerbations of autoimmune diseases during pregnancy and postpartum

Autoimmune diseases represent a complex heterogeneous group of disorders that occur as a results of immune homeostasis dysregulation and loss of self-tolerance. Interestingly, more than 80% of the cases are found among women at reproductive age. Normal pregnancy is associated with remarkable changes in the immune and endocrine signaling required to tolerate and support the development and survival of the placenta and the semi-allogenic fetus in the hostile maternal immune system environment. Gravidity and postpartum represent an extremely challenge period, and likewise the general population, women suffering from autoimmune disorders attempt pregnancy. Effective preconception counseling and subsequent gestation and postpartum follow-up are crucial for improving mother and child outcomes. This comprehensive review provides information about the different pathways modulating autoimmune diseases activity and severity, such as the influence hormones, microbiome, infections, vaccines, among others, as well as updated recommendations were needed, in order to offer those women better medical care and life quality.

Role of Fetal Stem Cells in Maternal Tissue Regeneration

Microchimerism refers to the status of harboring cells from another individual at low levels. It is well known that cells traffic bidirectionally between fetus and mother during pregnancy. This situation resembles a naturally occurring long lasting fetal stem cell transplantation. The fetus acts as the donor and the mother acts as the recipient. To study the role of microchimerism in tissue regeneration, we constructed a murine microchimerism model with wild type C57BL/6J female mice carrying progenies which expressed green fluorescent proteins (GFP). Our data indicated that skin injuries in the female mice during pregnancy increased microchimerism of GFP expressing cells from the GFP transgenic progenies. The GFP positive cells also appeared at the site of spinal cord where injury occurred during pregnancy. Our study suggests that the amount of fetal cells in maternal mice significantly increased if injuries occurred during pregnancy. Fetal stem cells appear to respond to maternal injury signals and may play a role in maternal tissue regeneration during pregnancy.

Epigenetic approaches for the detection of fetal DNA in maternal plasma

The presence of fetal DNA in the plasma of pregnant women has opened up new possibilities for noninvasive prenatal diagnosis. Over the past decades, different types of fetal markers have been developed, initially based on discriminative genetic markers such as male-specific signals or paternally-inherited polymorphisms, and gradually evolved to the detection of fetal-specific transcripts or epigenetic signatures. This development has extended the coverage of the application of cell-free fetal DNA to essentially all pregnancies, regardless of the gender of the fetus or its polymorphic status. In this review, we present an overview of the development of noninvasive prenatal diagnosis through epigenetics. We introduce the basis of how fetal DNA could be detected from a large background of maternal DNA in maternal plasma based on fetal-specific DNA methylation patterns. We evaluate the methodologies involved and discuss the factors that affect the robustness of the detection. We review the progress in adopting fetal epigenetic markers for noninvasive prenatal assessment of fetal chromosomal aneuploidies and pregnancy-associated disorders. We conclude with comments on the future directions regarding the search for new fetal epigenetic markers and the clinical implementation of epigenetic approaches for noninvasive prenatal diagnosis.

Fetal microchimerism persists at high levels in c-kit stem cells in sensitized mothers

We previously showed that fetal and maternal exposure to non-inherited maternal antigens (NIMA) during gestation and nursing resulted in lifelong tolerance to NIMA in some offspring. This NIMA-specific tolerance was mediated by regulatory T cells (Tregs) and was correlated with the level of multi-lineage maternal microchimerism (Mc) indicating a causative link between Mc and Treg development. To determine if transfer of fetal cells into mothers resulted in a similar tolerance to fetal cells, we used qPCR to detect rare fetal derived cells and a delayed type hypersensitivity (DTH) assay to detect fetal alloantigen-specific effector and regulatory T cells in mothers. We found that 5/8 B6 mothers of H2(b/d) offspring were sensitized to the alloantigens H2(d) and HY, indicating a dominance of alloantigen-specific effector T cells. Though these sensitized mothers did not have detectable fetal Mc (FMc) in any of the organs tested, they had very high levels of fetus-derived c-kit(+) stem cells in their bone marrow. The remaining 3/8 B6 mothers that were not sensitized to the fetal antigens had detectable FMc found mostly in heart, lungs and liver, and in 2/3, we could detect alloantigen-specific regulatory T cells. This data indicates that, as in NIMA-specific tolerance, tolerance in multiparous females to inherited paternal antigens (IPA) expressed by the fetus is associated with the presence of fetal Mc in differentiated cell subsets. Surprisingly, robust lin(-)c-kit(+) bone marrow cell fetal Mc can occur in sensitized mothers. This suggests a continuous source of allospecific priming, coupled with active elimination of mature IPA-expressing lin(+) cells by effector T cells of the maternal host.

Pregnancy, microchimerism and autoimmunity: an update

The presence of a small population of cells or DNA in one individual that derives from another genetically distinct person is referred to as microchimerism; this process may occur in course of pregnancy from mother to fetus, and vice versa. The clinical similarities between some features of autoimmune diseases and the chronic graft versus host disease, the increased incidence of autoimmune diseases observed in women after childbearing age, and the long-term persistence of microchimerism have raised the hypothesis that microchimerism could be involved in the pathogenesis of autoimmune diseases. To assess the possible relationship between pregnancy and the incidence of systemic sclerosis we performed a hospital-based case-control study. Our results, indicating a reduced risk for systemic sclerosis in women who had been pregnant in comparison with women who had not, seem to indicate that pregnancy is not a risk factor for systemic sclerosis.

Sex differences in Sjögren's syndrome: a comprehensive review of immune mechanisms

Autoimmune diseases (ADs) are estimated to affect between 5 and 8 % of the US population, and approximately 80 % of these patients are women. Sjögren’s syndrome (SS) is an AD that occurs predominately in women over men (16:1). The hallmark characteristic of SS is diminished secretory production from the primary exocrine gland and the lacrimal or salivary glands resulting in symptoms of dry eye and mouth. The disease is believed to be mediated by an inflammatory and autoantibody response directed against salivary and lacrimal gland tissues. This review will examine the literature on sex differences in the immune response of patients and animal models of Sjögren’s syndrome in order to gain a better understanding of disease pathogenesis.

Feto-maternal allo-immunity, regulatory T cells and predisposition to auto-immunity. Does it all start in utero?

During gestation, maternal cells traffic to the fetus leading to the natural phenomenon of microchimerism. Although their persistence in offspring has been associated with several autoimmune disorders, the precise role of maternal cells in these disorders remains unclear. We aimed to evaluate whether alloreactive maternal T cells could directly trigger a graft-vs.-host like reaction or indirectly influence the development of the offspring's regulatory T cells (Treg) favoring autoimmunity. In a specific breeding strategy, we recently reported that maternal allogeneic T cells changed fetal Treg development and their quantities in mesenteric lymph nodes, leading to early signs of inflammation in the gut later in life. Although maternal microchimeric T cells were found in newborn tissues, we could not detect any cells in the gut from adult offspring where the inflammation occurred. Thus, strongly alloreactive maternal microchimeric T cells may indirectly drive the offspring to gut inflammation. We believe these results suggest a new mechanism for predisposition to auto-immunity.

Lack of Evidence That Male Fetal Microchimerism is Present in Endometriosis

INTRODUCTION

Fetal microchimerism has been implicated in the etiology of autoimmune diseases. This study was done to test the hypothesis that male fetal microchimerism is present in eutopic and ectopic endometrium (EM) obtained from women with endometriosis but not in eutopic EM from women without endometriosis.

METHODS

A total of 31 patients were selected, including women with endometriosis (paired eutopic and ectopic EM; n = 19) and women without endometriosis (eutopic EM; n = 12). Tricolor interphase fluorescence in situ hybridization analysis was performed by cohybridization of CEP Y SpectrumAqua and CEP X SpectrumGreen (SG)/CEP Y SpectrumOrange probes.

RESULTS

Ectopic EM from women with endometriosis had 75% XX chromosomes (double SG signals) and 25% X chromosomes (single SG signal). Y chromosomes were not observed in any of the eutopic/ectopic endometrial tissues from cases or controls.

CONCLUSIONS

We were unable to confirm our hypothesis that male fetal microchimerism is present in eutopic and/or ectopic EM obtained from women with endometriosis.

Follow-up study of lympho-histiocytic villitis and incidental retroplacental hematoma

Placentas are usually submitted for pathologic examination based on obstetrical indications. We hypothesized that the placenta may have diagnostic value to the infant independent of obstetrical events. We specifically tested whether lymphohistiocytic villitis (noninfectious) would predict autoimmune or alloimmune disease based on transfer of activated maternal T-cells to the fetus and whether clinically silent placental separations (retroplacental hematomas, RPH) would predict neurologic injury in the infant. All placentas from consecutive deliveries had a routine pathologic examination of the placenta. The infants with placentas demonstrating inflammation of >1% of villi or RPH >2 cm and matched controls had their hospital charts reviewed and parental interviews by telephone at 5 to 7 years of age. The children of consented patients were also searched for in the office visits of the University of Louisville Pediatric Neurology and Rheumatology divisions. One thousand six hundred eighty-four patients consented to the follow-up study. We found no cases of autoimmune disease among 17 children with villitis >1%. Of 16 infants with RPH, 1 had cerebral palsy but with other placental findings, 1 had lethal hydranenecephaly, and the remainder had no adverse outcome. Of 15 children seen by a pediatric neurologist, none had the same placental lesion. The specific lesions of lymphohistiocytic villitis or asymptomatic RPH do not predict significant pediatric disease by 7 years of age. At least for these 2 lesions, the placenta does not have diagnostic value to the infant.

Selective organ specific inflammation in offspring harbouring microchimerism from strongly alloreactive mothers

The origins of autoimmunity are not yet understood despite significant advances in immunology. The trafficking of maternal cells to the offspring represents the very first immunological event in foetal life and is reinforced during lactation. The persistence of maternal cells in offspring's tissues and circulation has been associated with several autoimmune disorders. However a direct causal effect has never been demonstrated. Maternal T cells specifically targeting foetal insulin producing cells have been shown to generate islet inflammation without directly participating in this process. Our objective was to evaluate if alloreactive maternal cells could directly trigger a graft-versus host like reaction or indirectly influence the development of the offspring's regulatory T cells favouring autoimmunity. We adopted a breeding strategy comparing genetically identical offspring from either strongly alloreactive transgenic mothers compared to immunodeficient mothers. We detected maternal alloreactive T cells in the offspring and early signs of inflammation in small intestine of 6 weeks old offspring. Interestingly, CD4(+) Foxp3(+) regulatory T cell frequency was diminished in mesenteric lymph nodes from eight months old offspring born of alloreactive mothers compared to offspring of immunodeficient mothers. Our study favours a hypothesis where highly alloreactive maternal cell microchimerism indirectly predisposes offspring to autoimmunity.

Long-term persistence and effects of fetal microchimerisms on disease onset and status in a cohort of women with rheumatoid arthritis and systemic lupus erythematosus

Background

The discovery of a fetal cells transfer to the mother is a phenomenon with multiple implications for autoimmunity and tolerance. The prevalence and meaning of the feto-maternal microchimerism (MC) in rheumatic diseases has not been thoroughly investigated. The aim of this study was to analyze the prevalence of fetal MC in patients with inflammatory rheumatic diseases and to investigate the association of MC with disease onset and current status.

Methods

A total of 142 women who gave birth to at least one male offspring were recruited: 72 women with rheumatoid arthritis (RA), 16 women with systemic lupus erythematosus (SLE), and 54 healthy women. For the detection of fetal microchimerism a nested PCR method was used to amplify a Y chromosome specific sequence (TSPY1). For characterization of disease activity we analyzed autoantibody profiles and X-rays in RA, and in addition complement levels in SLE respectively.

Results

A significant higher prevalence of fetal MC was found in RA (18%) and SLE (31%) compared to controls (3.7%) (p = 0.02 and p = 0.006, resp.). The mean age at disease onset was comparable in MC + and MC- RA patients. Disease onset occurred 18.7 (MC +) and 19.8 (MC-) years post partum of the first son, respectively. The presence of anti-CCP and RF did not differ significantly, anti-CCP were found in 75% of MC + and 87% of MC- patients, RF in 75% of both MC + and MC- patients. A slightly higher mean Steinbrocker score in MC + patients was associated with longer disease duration in MC + compared to MC- RA. In SLE patients the mean age at disease onset was 42.6 years in MC + and 49.1 years in MC- patients. Disease onset occurred 24.0 and 26.4 years post partum of the first son for MC + and MC- patients, respectively. The presence of ANA and anti-dsDNA antibodies, C3, C4 and CH50 did not differ significantly.

Conclusion

Our results indicate a higher frequency of long-term male MC in RA and SLE patients compared with controls without impact on disease onset and status in RA and SLE.

Fetal microchimeric cells in blood and thyroid glands of women with an autoimmune thyroid disease

Persistence of fetal microchimeric cells may result in the development of autoimmune thyroid diseases (AITD) such as Hashimoto thyroiditis (HT) or Graves disease (GD). In women, HT and GD show an increased incidence in the years following parturition. Although fetal cells have already been shown to be more common in the thyroid glands of patients with an AITD compared with controls, these cells haven’t been described in blood of these patients. Our study detected fetal cells in blood of all patients with an AITD. Moreover, fetal cells were immune cells potentially capable of initiating a graft vs. host reaction and suggest a potential role of these cells in the pathogenesis of AITD. Our study indicates the value and need for further research in this field.

Fetal microchimeric cells in autoimmune thyroid diseases: harmful, beneficial or innocent for the thyroid gland?

Autoimmune thyroid diseases (AITD) show a female predominance, with an increased incidence in the years following parturition. Fetal microchimerism has been suggested to play a role in the pathogenesis of AITD. However, only the presence of fetal microchimeric cells in blood and in the thyroid gland of these patients has been proven, but not an actual active role in AITD. Is fetal microchimerism harmful for the thyroid gland by initiating a Graft versus Host reaction (GvHR) or being the target of a Host versus Graft reaction (HvGR)? Is fetal microchimerism beneficial for the thyroid gland by being a part of tissue repair or are fetal cells just innocent bystanders in the process of autoimmunity? This review explores every hypothesis concerning the role of fetal microchimerism in AITD.

Sex-related factors in multiple sclerosis susceptibility and progression

The pathogenesis of multiple sclerosis (MS) involves complex interactions between genetic susceptibility and environmental triggers. Clinical observations suggest that the study of sex differences might provide important insight into mechanisms of pathogenesis and progression of the disease in patients. MS occurs more frequently in women than in men, indicating that sex-related factors have an effect on an individual's susceptibility to developing the condition. These factors include hormonal, genetic and environmental influences, as well as gene-environment interactions and epigenetic mechanisms. Interestingly, women do not have a poorer prognosis than men with MS despite a higher incidence of the disease and more-robust immune responses, which suggests a mechanism of resilience. Furthermore, the state of pregnancy has a substantial effect on disease activity, characterized by a reduction in relapse rates during the third trimester but an increased relapse rate in the postpartum period. However, pregnancy has little effect on long-term disability in women with MS. The unravelling of the mechanisms underlying these clinical observations in the laboratory and application of the results to the clinical setting is a unique and potentially fruitful strategy to develop novel therapeutic approaches for MS.

Fetal microchimeric cells in blood of women with an autoimmune thyroid disease

Context

Hashimoto's thyroiditis (HT) and Graves' disease (GD), two autoimmune thyroid diseases (AITD), occur more frequently in women than in men and show an increased incidence in the years following parturition. Persisting fetal cells could play a role in the development of these diseases.

Objective

Aim of this study was to detect and characterize fetal cells in blood of postpartum women with and without an AITD.

Participants

Eleven patients with an AITD and ten healthy volunteers, all given birth to a son maximum 5 years before analysis, and three women who never had been pregnant, were included. None of them had any other disease of the thyroid which could interfere with the results obtained.

Methods

Fluorescence in situ hybridization (FISH) and repeated FISH were used to count the number of male fetal cells. Furthermore, the fetal cells were further characterized.

Results

In patients with HT, 7 to 11 fetal cells per 1.000.000 maternal cells were detected, compared to 14 to 29 fetal cells in patients with GD (p = 0,0061). In patients with HT, mainly fetal CD8⁺ T cells were found, while in patients with GD, fetal B and CD4⁺ T cells were detected. In healthy volunteers with son, 0 to 5 fetal cells were observed, which was significantly less than the number observed in patients (p<0,05). In women who never had been pregnant, no male cells were detected.

Conclusion

This study shows a clear association between fetal microchimeric cells and autoimmune thyroid diseases.

Antithyroid antibodies and parity: further evidence for microchimerism in autoimmune thyroid disease

OBJECTIVE

Fetal microchimerism may have a role in development of autoimmune thyroid disorders. Using parity as a surrogate for increasing fetal cell exposure, we analyzed its association with thyroid peroxidase antibody levels.

STUDY DESIGN

Secondary analysis of serum thyroid analytes determined in 17,298 women from a population-based prospective study between 2001 and 2003. Sera were assayed for thyrotropin, free thyroxine, and antithyroid peroxidase antibodies. We analyzed the relationship between thyroid peroxidase antibodies and increasing parity.

RESULTS

The incidence of abnormally elevated thyroid peroxidase antibody levels (>50 IU/mL) increased with advancing parity, but was not significant after adjustment for maternal characteristics. However, at higher thyroid peroxidase antibody levels (>500 IU/mL), a significant relationship with advancing parity persisted after adjustments (P = .002).

CONCLUSION

Advancing parity is associated with an increased risk for high serum concentrations of antithyroid peroxidase antibodies. This suggests fetal microchimerism may play a role in development of autoimmune thyroid disorders.

Pregnancy and the risk of autoimmune disease

Autoimmune diseases (AID) predominantly affect women of reproductive age. While basic molecular studies have implicated persisting fetal cells in the mother in some AID, supportive epidemiological evidence is limited. We investigated the effect of vaginal delivery, caesarean section (CS) and induced abortion on the risk of subsequent maternal AID. Using the Danish Civil Registration System (CRS) we identified women who were born between 1960 and1992. We performed data linkage between the CRS other Danish national registers to identify women who had a pregnancy and those who developed AID. Women were categorised into 4 groups; nulligravida (control group), women who had 1st child by vaginal delivery, whose 1st delivery was by CS and who had abortions. Log-linear Poisson regression with person-years was used for data analysis adjusting for several potential confounders. There were 1,035,639 women aged >14 years and 25,570 developed AID: 43.4% nulligravida, 44.3% had their first pregnancy delivered vaginally, 7.6% CS and 4.1% abortions. The risk of AID was significantly higher in the 1st year after vaginal delivery (RR = 1.1[1.0, 1.2]) and CS (RR = 1.3[1.1, 1.5]) but significantly lower in the 1st year following abortion (RR = 0.7[0.6, 0.9]). These results suggest an association between pregnancy and the risk of subsequent maternal AID. Increased risks of AID after CS may be explained by amplified fetal cell traffic at delivery, while decreased risks after abortion may be due to the transfer of more primitive fetal stem cells. The increased risk of AID in the first year after delivery may also be related to greater testing during pregnancy.

[Fetal microchimerism: self and non-self, finally who are we?]

For a long time, the conventional view was that the fetus and maternal vascular system are kept separate. In fact there is a two-way traffic of immune cells through the placenta and the transplacental passage of cells is in fact the norm. The fetal cells can persist in a wide range of woman's tissue following a pregnancy or an abortion and she becomes a chimera. Fetal cells have been found in the maternal circulation and they were shown to persist for almost three decades in humans, thus demonstrating long-term engraftment and survival capabilities. Microchimerism is a subject of much interest for a number of reasons. Studies of fetal microchimerism during pregnancy may offer explanations for complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune disease which usually ameliorates during pregnancy. The impact that the persistence of allogenic cells of fetal origin and the maternal immunological response to them has on the mother's health and whether it is detrimental or beneficial to the mother is still not clear. Although microchimerism has been implicated in some autoimmune diseases, fetal microchimerism is common in healthy individuals. On the beneficial side, it has been proposed that genetically disparate fetal microchimerism provides protection against some cancers, that fetal microchimerism can afford the mother new alleles of protection to some diseases she has not, that fetal microchimerism can enlarge the immunological repertoire of the mother improving her defense against aggressor. Fetal cells are often present at sites of maternal injury and may have an active role in the repair of maternal tissues.

Fetally derived CCL3 is not essential for the migration of maternal cells across the blood-placental barrier in the mouse

In mammals with a hemochorial placenta (e.g., primates and rodents), the maternal and fetal bloodstreams are separated by the blood-placenta barrier. However, a few maternal cells in the general circulation pass through the barrier during normal pregnancy. So far, the transfer mechanism has not been investigated. In this study, we established a chemokine (C-C motif) ligand 3 (CCL3)-deficient mouse model to examine the effect of fetus-derived chemokine(s) on the migration of maternal cells through the blood-placenta barrier. Using this model, we obtained CCL3-positive and -negative littermates from a mother expressing both CCL3 and green fluorescent protein (GFP). The numbers of GFP positive maternal cells in the lung, liver, spleen and heart of CCL3-positive and -negative fetuses were compared. A few GFP-positive cells were detected in the lung and liver of both types of fetus. These results indicate that maternal cells can migrate through the blood-placenta barrier even in the absence of fetal CCL3.

Genomic variants associated with primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune hepatobiliary disease characterized by immune-mediated injury of small and medium-sized bile ducts, eventually leading to liver cirrhosis. Several studies have addressed PBC immunopathology, and the data support an immune activation leading to autoantibodies and autoreactive T cells acting against the lipoylated 2-oxoacid dehydrogenase complexes. The causes of the disease remain unknown, but environmental factors and genetic susceptibility both contribute to its onset. Over the past two decades several association studies have addressed the role of genetic polymorphisms in PBC pathogenesis and have reported multiple associations. However, only a few studies had sufficient statistical power, and in most cases results were not independently validated. A genome-wide association study has recently been reported, but this too awaits independent confirmation. The aim of this present work is to critically review the numerous studies dedicated to revealing genetic associations in PBC, and to predict the potential for future studies based on these data.

Rheumatoid arthritis: Disease or syndrome?

Rheumatoid arthritis (RA) has been described in the medical literature for over two hundred years, but its etiology remains unknown. RA displays phenotypic heterogeneity, and it is a relatively prevalent clinical entity: it affects approximately 1% of the population, resulting in enormous pathologic sequelae. Earlier studies targeting the cause(s) of RA suggested potential infectious involvement, whereas more recent reports have focused on a genetic origin of the disease. However, neither infection nor genetics, nor any other single factor is currently accepted as causative of RA. In this article we review studies relating to the etiology of RA, and those of several related matters, and we conclude that the literature indeed does provide insight into the causes underlying the initiation of RA pathogenesis. Briefly, given the remarkable phenotypic variation of RA, especially in its early stages, as well as a number of other characteristics of the condition, we contend that RA is not a discrete clinical entity with a single etiological source. Rather, we argue that it represents a common clinical endpoint for various starting points, each of which is largely guided by as yet poorly understood aspects of the genetic background of the affected individual. Adoption of this alternative view of the origin of RA will have significant consequences for future research and for development of new therapeutic interventions for this burdensome condition.

Fetal cell microchimerism in human cancers

The transfer of fetal cells into the maternal circulation occurs normally during pregnancy and the post-partum persistence of these cells in the maternal blood and tissues, known as fetal cell microchimerism, has been clearly demonstrated. However, the long-term consequences of this phenomenon are only beginning to be appreciated. In particular, whether microchimerism could be involved in the carcinogenetic process or whether fetal microchimeric cells could be able to differentiate in host tissues, participating in the maternal response to injury, is still matter of study. In this review, the possible role and the consequences of fetal cell microchimerism, as emerged from studies in animal models and in women with different types of cancer, will be presented.

Fetal microchimerism and maternal health during and after pregnancy

Trafficking of fetal cells into the maternal circulation begins very early in pregnancy and the effects of this cell traffic are longlasting. All types of fetal cells, including stem cells, cross the placenta during normal pregnancy to enter maternal blood, from where they may be recovered in pregnancy for the purpose of genetic prenatal diagnosis. Fetal cells can also be located in maternal tissues during and after pregnancy, and persist as microchimeric cells for decades in marrow and other organs. Although persistent fetal cells were first implicated in autoimmune disease, subsequent reports routinely found microchimeric cells in healthy tissues and in non-autoimmune disease. Parallel studies in animal and human pregnancy now suggest instead that microchimeric fetal cells play a role in the response to tissue injury. However, it is still not clear whether microchimeric fetal cells persisting in the mother are an incidental finding, are naturally pathogenic or act as reparative stem cells, and the environmental or biological stimuli that determine microchimeric cell fate are as yet undetermined. Future studies must also focus on investigating whether fetal cells create functional improvement in response to maternal injury and whether this response can be manipulated. The pregnancy-acquired low-grade chimeric state of women could have far-reaching implications, influencing recovery after injury or surgery, ageing, graft survival after transplantation, survival after cancer as well as deciding the protective effect of pregnancy against diseases later in life. Lifelong persistence of fetal cells in maternal tissues may even explain why women live longer than men.

Fetal cells of mesenchymal origin in cultures derived from synovial tissue and skin of patients with rheumatoid arthritis

The transplacental cell transfer naturally takes place during pregnancy and occurs bi-directionally between the mother and fetus. Using real-time polymerase chain reaction (PCR) assay and sex determining region Y (SRY) gene as a marker, we examined the presence of male fetal cells in cell cultures derived from synovial tissues and skin dermis in women with prior pregnancy history suffering from rheumatoid arthritis (RA) who underwent synovectomy. Male DNA was detected in synovial cell samples derived from carpal, hip, metacarpophalangeal and metatarsophalangeal joints in five out of 13 (38.5%) patients with RA in a frequency range of 0.02-62.55 (mean 12.17) male cells per 10,000,000 total cells. SRY gene positivity was found as well in skin fibroblast cultures in four out of 10 (40.0%) RA patients in a frequency range of 3.26-43.47 (mean 15.42) male cells per 10,000,000 total cells, respectively. The difference in a frequency of fetal-derived male cells between both the cohorts did not achieve the statistical difference (p=0.77). We conclude that persisting male fetal cells are able to grow from non-inflamed tissues as well as from those which have many features characteristic of a stressed tissue. We conclude that persisting male fetal cells are also able to proliferate in cell culture since their presence was detected even in consecutive passages.

Microchimeric fetal cells cluster at sites of tissue injury in lung decades after pregnancy

Fetal cells trafficking into maternal blood during pregnancy engraft tissues and persist for decades in marrow and bone. While persistent fetal cells were initially implicated in autoimmune disease, animal studies suggest that microchimeric fetal cells play a broader role in response to tissue injury. This study investigated whether fetal cells participate in tissue repair after human pregnancy. Specimens were obtained from women undergoing surgery for suspected lung cancer. Y-fluorescence in-situ hybridization was performed on paraffin-embedded sections, with the investigator blinded to medical histories. Male cells were identified in lung/thymus tissue from all women with known male pregnancies, but not in those without sons. The frequency of male microchimeric cells was seven-fold greater in lung/thymus tissues than marrow and was two-fold greater than normal bone from the same women. Nested-polymerase chain reaction for sex determining region Y confirmed male DNA in tissues. Male cells in lung were clustered in tumour rather than surrounding healthy tissues. In conclusion, male presumed-fetal cells were identified in pathological post-reproductive tissues, where they were more likely to be located in diseased tissues at several-fold higher frequency than normal tissues. It is suggested that fetal cells are present at sites of tissue injury and may be stem cells, either recruited from marrow or having proliferated locally.

The TNF (-308A) polymorphism is associated with microchimerism in transfused trauma patients

Microchimerism (MC), defined as the persistence of allogeneic cells at low concentrations, is well documented in transfused trauma patients. We hypothesized that genetic polymorphisms linked to cytokine production could contribute to trauma-induced immune modulation and development of microchimerism after transfusion of trauma patients. We used high-throughput SYBR-green-based genotyping of single nucleotide polymorphisms (SNPs) to characterize 59 transfused trauma patients, with MC (n=30) and without MC (n=29), for 4 functionally significant SNPs: TNF (-308), IL 10 (-1082), IFNG (+874), and TGFB1 (+915). We then compared likelihood for development of MC and the magnitude of immune suppression among subjects with and without these selected immune response SNPs. We identified a significant association between TNF (-308A) SNP and both development of MC and diminished immune responsiveness. Hence predisposing genetic factors may explain, in part, why only a subset of trauma patients develops transfusion-associated microchimerism.

Frontiers of immunological tolerance

Herein, we succinctly review mechanisms underlying self-tolerance and the roles of dendritic leukocytes (DCs) in T-cell tolerance to self and foreign antigens. We also consider the properties of naturally arising and other populations of regulatory T cells (Treg), together with growing evidence that interplay between DCs and Treg cells can sustain antigen-specific tolerance. B-cell tolerance and the role of hematopoietic cell chimerism in the induction and maintenance of tolerance are also discussed, as is the impact of cosignaling pathway manipulation on tolerance induction. This overview also surveys prospects for technological advances in the monitoring and prediction of tolerance and the application of genomic and proteomic analysis. In addition, we consider potential novel therapeutic targets for promotion of tolerance induction.

The influence of pregnancy on the development of autoimmunity in chronic lymphocytic leukemia

To examine whether pregnancy influences the development of autoimmunity in chronic lymphocytic leukemia (CLL), we studied 591 consecutive CLL patients (202 post-menopausal women and 389 men). The mean observation time for all patients was 3.8 years, corresponding to approximately 2200 person-years of follow-up. Autoimmune manifestations were analyzed in 194 women with known obstetric history and known number of long-term sexual partners, and in the 389 male CLL patients for comparison. One hundred and fifty-nine of the CLL patients exhibited autoimmune manifestations, 38% in females and 21% in men. In female CLL patients, the frequency of autoimmunity and the number of pregnancies and the number of partners were strongly correlated. Each of the major autoimmune types approximately doubled in frequency for each additional pregnancy. The impact of pregnancy on expressed autoimmunity increased with each additional sexual partner (the odds of autoimmunity increased 11 times with each long-term sexual partner). The average numbers of pregnancies in female CLL patients with and without autoimmunity were 4.92 and 2.24, respectively (P < 0.001). Coombs' positive autoimmune anemia, a gastric ulcer with parietal cell autoantibodies and idiopathic thrombocytopenic purpura were equally common in women and men, whereas autoimmune thyroiditis, Sjögren's syndrome, rheumatoid arthritis and systemic lupus erythematosus were seen in higher rates in women than in men. The spectrum of autoimmunity suggests that pregnancy-related alloimmunization may be involved in the development of autoimmunity in CLL.