Fetal cellular microchimerism in miscarriage and pregnancy termination

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.

Fetal microchimerism and the two-stage model of preeclampsia

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

Microchimerism as a source of information on future pregnancies

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

The development of an indel panel for microchimerism detection

OBJECTIVES

The aim of the study was to create a simple assay for microchimerism detection independent of sex and without HLA genotyping.

METHODS

The method is based on detection of insertion or deletions utilizing a multiplex PCR followed by fragment analysis by capillary electrophoresis, and probe-based qPCR assays. A total of 192 samples, taken either before pregnancy, during 1st trimester, or either during 2nd trimester or at miscarriage, obtained from a cohort of 97 female patients with either primary or secondary recurrent pregnancy loss, were screened for fetal microchimerism by the indel panel as well as an existing assay based on detection of the Y-chromosome marker; DYS14.

RESULTS

The overall prevalence of DYS14 positive samples was 29% (55/192) whereas 32% (61/192) tested positive by the indel method. There was an overall agreement of 64% (122/192) between the results obtained by the two methods. A Fisher's Exact test showed no statistic significant difference in the prevalence of microchimerism detected by the two methods at any of the three times of sampling. The distribution of the number of positive wells detected by both methods were compared by a Mann-Whitney U test, which showed no statistically significant difference at any of the three times of sampling.

CONCLUSION

The data indicates that microchimerism can be detected efficiently by the indel method. This makes it possible to detect both female and male cells without the need of HLA-genotyping. Furthermore, the indel method has potential to be implemented as a routine analysis. This will remove the sex bias in future explorations of the role microchimerism plays in health and disease.

Male origin microchimerism and ovarian cancer

BACKGROUND

Reduced risk of ovarian cancer is commonly ascribed to reduced exposure to endogenous hormones during pregnancy, using oral contraceptives or not using hormone replacement therapy. However, exposure to hormones alone account for less than half of all cases. Many women carry small amounts of male cells-known as male origin microchimerism-in their circulation and remarkable impacts of these cells on women's health are being published. Here, we pursue the possibility that male origin microchimerism has a role in reducing ovarian cancer risk.

METHODS

We conducted a prospective case-cohort study using blood samples and questionnaire data from 700 women participating in the Danish Diet, Cancer, and Health cohort. Blood samples were analysed for Y chromosome presence as a marker of male microchimerism. We evaluated the association between male microchimerism and ovarian cancer, using weighted Cox regression models reporting hazard ratios (HRs) and corresponding 95% confidence intervals (CIs).

RESULTS

Male microchimerism was detected in 46% of cases and 65.9% of controls. Women testing positive for male microchimerism had a reduced hazard rate of ovarian cancer compared with women testing negative (HR = 0.44, 95% CI: 0.29-0.68). We found no evidence of interaction with measures of hormonal exposures (P = 0.50).

CONCLUSIONS

For the first time we report that women who test positive for male microchimerism in their circulation have reduced rates of ovarian cancer compared with women who test negative. Although the underlying mechanisms are presently unknown, we believe male microchimerism is potent in preventing ovarian cancer.

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.

Individuals, Boundaries, and Graft-versus-Host Disease

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

Fetal microchimerism in human brain tumors

Sex differences in cancer incidence and survival, including central nervous system tumors, are well documented. Multiple mechanisms contribute to sex differences in health and disease. Recently, the presence of fetal-in-maternal microchimeric cells has been shown to have prognostic significance in breast and colorectal cancers. The frequency and potential role of these cells has not been investigated in brain tumors. We therefore selected two common primary adult brain tumors for this purpose: meningioma, which is sex hormone responsive and has a higher incidence in women, and glioblastoma, which is sex hormone independent and occurs more commonly in men. Quantitative PCR was used to detect the presence of male DNA in tumor samples from women with a positive history of male pregnancy and a diagnosis of either glioblastoma or meningioma. Fluorescence in situ hybridization for the X and Y chromosomes was used to verify the existence of intact male cells within tumor tissue. Fetal microchimerism was found in approximately 80% of glioblastoma cases and 50% of meningioma cases. No correlations were identified between the presence of microchimerism and commonly used clinical or molecular diagnostic features of disease. The impact of fetal microchimeric cells should be evaluated prospectively.

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

The presence of fetal cells has been associated with both positive and negative effects on maternal health. These paradoxical effects may be due to the fact that maternal and offspring fitness interests are aligned in certain domains and conflicting in others, which may have led to the evolution of fetal microchimeric phenotypes that can manipulate maternal tissues. We use cooperation and conflict theory to generate testable predictions about domains in which fetal microchimerism may enhance maternal health and those in which it may be detrimental. This framework suggests that fetal cells may function both to contribute to maternal somatic maintenance (e.g. wound healing) and to manipulate maternal physiology to enhance resource transmission to offspring (e.g. enhancing milk production). In this review, we use an evolutionary framework to make testable predictions about the role of fetal microchimerism in lactation, thyroid function, autoimmune disease, cancer and maternal emotional, and psychological health.

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