Maternal-fetal immunology and autoimmune disease: is some autoimmune disease auto-alloimmune or allo-autoimmune?

Fetal cell microchimerism and cancer: a nexus of reproduction, immunology, and tumor biology

Fetal cell microchimerism (FCM) is the persistence of fetal cells in the maternal circulation and organs following pregnancy. Proposed hypotheses about the function of fetal cells in the pathogenesis of maternal cancer include promotion of tumorigenesis, protection by providing immunosurveillance, and participation in tissue repair. To date, studies of FCM and cancer have been primarily descriptive and quantitative. More research is needed to understand the cellular phenotype of the microchimeric cells in maternal tumors and whether they have a functional role. This research will require further study using a multidisciplinary approach, incorporating knowledge of the fetomaternal relationship, tumor biology, immunology, and clinical oncology.

Fetal microchimerism and women's health: a new paradigm

Pregnancy is associated with transfer of maternal cells to the fetus and fetal cells to the mother. In both cases, the transferred cells are described as microchimeric. Fetal microchimeric cells include semi-allogeneic stem cells, which are few in number and are capable of long-term survival in the "foreign" host. They are recognized by the maternal immune system but not rejected or attacked. These cells appear to survive and even thrive for years in a mother's body, perhaps for her lifetime. Previously regarded as potentially dangerous interlopers that might propagate autoimmune and even malignant disease, fetal microchimeric cells are now increasingly being recognized and analyzed for their healing, reparative, and perhaps regenerative roles. Fetal microchimerism (MC) may make significant and previously unknown positive contributions to women's health, longevity, and risk of disease. This article reviews the history, major discoveries, and current concepts and gaps in knowledge in the field of fetal MC.

Pregnancy-associated progenitor cells differentiate and mature into neurons in the maternal brain

Bidirectional cell trafficking between fetus and mother during pregnancy is a well-established phenomenon observed in placental vertebrates including humans. Although studies have shown that transmigratory fetal cells, also termed pregnancy-associated progenitor cells (PAPCs), can integrate into multiple maternal organs, the integration, long-term survival, and differentiation of PAPCs in the brain has not been extensively studied. Using a murine model of fetomaternal microchimerism, we show that PAPCs integrated and persisted in several areas of the maternal brain for up to 7 months postpartum. Besides expressing neural stem cell or immature neuronal markers, PAPCs were observed to express mature neuronal markers, indicating that PAPCs adopted a neuronal fate. Further, PAPCs also displayed morphologically neuronal maturation by an increasing axonal/dendritic complexity over time. Therefore, PAPCs seem to undergo a molecular and morphological maturation program similar to that observed during adult neurogenesis. We provide evidence that neuronal gene expression of PAPCs was not a consequence of cell fusion with maternal neurons. In addition, in mothers with experimentally induced Parkinson's disease (PD), the frequency of PAPCs within the hippocampus initially increased whereas long-term presence of PAPCs was compromised. Also, the spatial distribution of PAPCs within the hippocampus was altered in mothers with PD. Thus, the disease context influenced the initial attraction, long-term survival, and spatial distribution of PAPCs, which may have wider implications on cell replacement strategies in human neurodegenerative diseases such as PD.

Naturally acquired microchimerism

Bi-directional transplacental trafficking occurs routinely during the course of normal pregnancy, from fetus to mother and from mother to fetus. In addition to a variety of cell-free substances, it is now well recognized that some cells are also exchanged. Microchimerism refers to a small number of cells (or DNA) harbored by one individual that originated in a genetically different individual. While microchimerism can be the result of iatrogenic interventions such as transplantation or transfusion, by far the most common source is naturally acquired microchimerism from maternal-fetal trafficking during pregnancy. Microchimerism is a subject of much current interest for a number of reasons. During pregnancy, fetal microchimerism can be sought from the mothers blood for the purpose of prenatal diagnosis. Moreover, studies of fetal microchimerism during pregnancy may offer insight into complications of pregnancy, such as preeclampsia, as well as insights into the pathogenesis of autoimmune diseases such as rheumatoid arthritis which usually ameliorates during pregnancy. Furthermore, it is now known that microchimerism persists decades later, both fetal microchimerism in women who have been pregnant and maternal microchimerism in her progeny. Investigation of the long-term consequences of fetal and maternal microchimerism is another exciting frontier of active study, with initial results pointing both to adverse and beneficial effects. This review will provide an overview of microchimerism during pregnancy and of current knowledge regarding long-term effects of naturally acquired fetal and maternal microchimerism.

Fetal cell microchimerism in cancer: a meaningful event?

The influence of pregnancy on the occurrence and evolution of maternal tumors has been long debated. Breast carcinomas or melanomas have been suspected to be more severe during gestation. Recently, many investigators have described the transfer and persistence of fetal cells in maternal circulation and tissues during and after pregnancy. These fetal microchimeric cells have been described in a variety of maternal injured tissues where they displayed the host-tissue phenotype. Given the wide variety of injury and tissue types described, cancer has appeared as a potential situation that could be influenced by fetal microchimeric cells. This new unexplored effect of gestation on tumor course has been hypothesized as either protective against cancer, via the activity of allogenic fetal cells, or as promoting cancer, via a supportive role of fetal microchimeric cells in the tumor stroma. In this review, we will detail recent data supporting these hypotheses.

Fetal microchimerism: the cellular and immunological legacy of pregnancy

During pregnancy there is transplacental traffic of fetal cells into the maternal circulation. Remarkably, cells of fetal origin can then persist for decades in the mother and are detectable in the circulation and in a wide range of tissues. Maternal CD8 T cell responses directed against fetal antigens can also be detected following pregnancy. However, the impact that the persistence of allogenic cells of fetal origin and the maternal immune response towards them has on the mother's health remains unclear and is the subject of considerable investigation. The potentially harmful effects of fetal microchimerism include an association with autoimmune disease and recurrent miscarriage. Beneficial effects that have been explored include the contribution of persistent fetal cells to maternal tissue repair. A link between fetal microchimerism and cancer has also been proposed, with some results supporting a protective role and others, conversely, suggesting a role in tumour development. The phenomenon of fetal microchimerism thus provokes many questions and promises to offer further insights not only into the biology of pregnancy but fields such as autoimmunity, transplantation biology and oncology.

Fetal-maternal exchange of multipotent stem/progenitor cells: microchimerism in diagnosis and disease

The biological concept of microchimerism, the bidirectional trafficking and stable long-term persistence of small numbers of allogeneic (fetal and maternal) cells in a genetically different organ, has gained considerable attention. Microchimerism is a common phenomenon in many species, including humans, and microchimeric cells can modify immunological recognition or tolerance, affect the course and outcome of various diseases and demonstrate stem cell-like or regenerative potential. Here, we review current knowledge of the biology of microchimerism and show how long-term allogeneic co-existence within an organism can impact on existing paradigms in chronic disease, cancer biology, regenerative medicine and fetal-maternal immunology. We discuss diagnostic challenges, clinical applications and future research directions in this exciting and rapidly emerging field of allogeneic fetal-maternal cell exchange.

Mechanisms of sex difference: a historical perspective

OBJECTIVE

The history of the discovery of mechanisms contributing to sex difference helps to better appreciate gender factors in a variety of disease states. The objective of this article is to illustrate four mechanisms of sex differences in disease incidence: X-linkage (including inactivation, escape from inactivating, skewed inactivation), sex-specific exposure to disease-producing pathogens, fetal microchimerism, and iron depletion.

METHODS

This is a historic review.

RESULTS

An emphasis on sex difference led to the uncovering of four different mechanisms by which illness rates differ in men and women.

CONCLUSIONS

Research into many disease states can benefit from a focus on potential mechanisms that yield sex differences in illness susceptibility, progression, and outcome.

Biological implications of bi-directional fetomaternal cell traffic: a summary of a National Institute of Child Health and Human Development-sponsored conference

OBJECTIVE

The National Institute of Child Health and Human Development (NICHD) held a workshop on 27-28 July 2000 to bring together investigators working in the field of fetomaternal cellular and nucleic acid trafficking with the hope that this would stimulate further research into the biological implications of such phenomena.

METHODS

Invited speakers from all over the world presented their latest (unpublished) data. The conference proceedings were delayed until the present time to allow independent publication of the primary data.

RESULTS AND CONCLUSIONS

Bi-directional fetomaternal trafficking of cells and nucleic acids during pregnancy is now well established, through the use of molecular techniques including conventional and real-time polymerase chain reaction, as well as fluorescence in situ hybridization. In addition, human leukocyte antigen (HLA) is deposited in the skin of pregnant women. Fetomaternal trafficking is increased in some complications of pregnancy, such as pre-eclampsia, polyhydramnios, polymorphic eruption of pregnancy, preterm labor and specific fetal chromosome aneuploidies. Maternal cells and nucleic acids have been documented in umbilical cord blood and in autopsy tissue of non-transfused neonates. Fetal cells persist postpartum and may be associated with the development of disorders such as scleroderma, lichen planus, lupus and thyroid disease. The extent of fetomaternal trafficking may be affected by three generational HLA relationships. Thus, the consequences of pregnancy extend beyond gestation.

Fetal cells in the pregnant mouse are diverse and express a variety of progenitor and differentiated cell markers

To better understand fetomaternal cell trafficking during pregnancy, we used a mouse model to determine the cell surface markers expressed on fetal cells, based on the hypothesis that fetal progenitor cells have the capacity to repair maternal organs, whereas more differentiated cells might initiate graft versus host disease. Wild-type females were mated to either homozygous or hemizygous transgenic males and euthanized in the peripartum period. Using dual color flow cytometry, we analyzed fetal transgene positive cells for the presence of nine markers (ITGAM, ITGB1, PECAM, CD34, CD44, PTPRC, ENG, SLAMF1, and CXCR4) to begin to identify the phenotype and degree of differentiation of fetal cells in nine maternal organs (lung, liver, spleen, blood, bone marrow, kidney, heart, thymus, and brain). Fetal cells were found in all maternal organs following either type of mating, albeit always at a higher frequency following mating with homozygous males. Some organs (e.g., lung and liver) had a wide variety of fetal cell markers present, while other organs (e.g., bone marrow and spleen) had a skewed distribution of fetal cell markers. Fetal cells in the murine pregnant female are diverse. Our results suggest that the fetal cells comprise a mixed population of progenitor and differentiated cells, with different relative proportions in different maternal organs. Future studies will address whether fetal cells cross the placental barrier in a differentiated state or as a homogenous population and subsequently differentiate in target maternal organs.

Chimeric maternal cells with tissue-specific antigen expression and morphology are common in infant tissues

Maternal microchimerism (MMc) has been purported to play a role in the pathogenesis of autoimmunity, but how a small number of foreign cells could contribute to chronic, systemic inflammation has not been explained. Reports of peripheral blood cells differentiating into tissue-specific cell types may shed light on the problem in that chimeric maternal cells could act as target cells within tissues. We investigated MMc in tissues from 7 male infants. Female cells, presumed maternal, were characterized by simultaneous immunohistochemistry and fluorescence in situ hybridization for X- and Y-chromosomes. Maternal cells constituted 0.017% to 1.9% of parenchymal cells and were found in all infants in liver, pancreas, lung, kidney, bladder, skin, and spleen. Maternal cells were differentiated: maternal hepatocytes in liver, renal tubular cells in kidney, and beta-islet cells in pancreas. Maternal cells were not found in areas of tissue injury or inflammatory infiltrate. Maternal hematopoietic cells were found only in hearts from patients with neonatal lupus. Thus, differentiated maternal cells are present in multiple tissue types and occur independently of inflammation or tissue injury. Loss of tolerance to maternal parenchymal cells could lead to organ-specific "auto" inflammatory disease and elimination of maternal cells in areas of inflammation.

Sex-specific genetic architecture of human disease

Sexual dimorphism in anatomical, physiological and behavioural traits are characteristics of many vertebrate species. In humans, sexual dimorphism is also observed in the prevalence, course and severity of many common diseases, including cardiovascular diseases, autoimmune diseases and asthma. Although sex differences in the endocrine and immune systems probably contribute to these observations, recent studies suggest that sex-specific genetic architecture also influences human phenotypes, including reproductive, physiological and disease traits. It is likely that an underlying mechanism is differential gene regulation in males and females, particularly in sex steroid-responsive genes. Genetic studies that ignore sex-specific effects in their design and interpretation could fail to identify a significant proportion of the genes that contribute to risk for complex diseases.

Autoimmune disease during pregnancy and the microchimerism legacy of pregnancy

Pregnancy has both short-term effects and long-term consequences on the maternal immune system. For women who have an autoimmune disease and subsequently become pregnant, pregnancy can induce amelioration of the mother's disease, such as in rheumatoid arthritis, while exacerbating or having no effect on other autoimmune diseases like systemic lupus erythematosus. That pregnancy also leaves a long-term legacy has recently become apparent by the discovery that bi-directional cell trafficking results in persistence of fetal cells in the mother and of maternal cells in her offspring for decades after birth. The long-term persistence of a small number of cells (or DNA) from a genetically disparate individual is referred to as microchimerism. While microchimerism is common in healthy individuals and is likely to have health benefits, microchimerism has been implicated in some autoimmune diseases such as systemic sclerosis. In this paper, we will first discuss short-term effects of pregnancy on women with autoimmune disease. Pregnancy-associated changes will be reviewed for selected autoimmune diseases including rheumatoid arthritis, systemic lupus erythematosus and autoimmune thyroid disease. The pregnancy-induced amelioration of rheumatoid arthritis presents a window of opportunity for insights into both immunological mechanisms of fetal-maternal tolerance and pathogenic mechanisms in autoimmunity. A mechanistic hypothesis for the pregnancy-induced amelioration of rheumatoid arthritis will be described. We will then discuss the legacy of maternal-fetal cell transfer from the perspective of autoimmune diseases. Fetal and maternal microchimerism will be reviewed with a focus on systemic sclerosis (scleroderma), autoimmune thyroid disease, neonatal lupus and type I diabetes mellitus.

Skewed X-chromosome inactivation in scleroderma

Scleroderma is a female-prevalent autoimmune disease of unclear etiology. Two fundamental gender differences, skewed X-chromosome inactivation (XCI) and pregnancy-related microchimerism, have been implicated in scleroderma. We investigated the XCI patterns of female scleroderma patients and the parental origin of the inactive X chromosome in those patients having skewed XCI patterns (>80%). In addition, we investigated whether a correlation exists between XCI patterns and microchimerism in a well-characterized cohort. About 195 female scleroderma patients and 160 female controls were analyzed for the androgen receptor locus to assess XCI patterns in the DNA extracted from peripheral blood cells. Skewed XCI was observed in 67 (44.9%) of 149 informative patients and in 10 of 124 healthy controls (8.0%) [odds ratio (OR) = 9.3 (95% confidence interval (CI) 4.3-20.6, P < 0.0001)]. Extremely skewed XCI (>90%) was present in 44 of 149 patients (29.5%) but only in 3 of 124 controls (2.4%; OR = 16.9; 95% CI 4.8-70.4, P < 0.0001). Parental origin of the inactive X chromosome was investigated for ten patients for whom maternal DNA was informative, and the inactive X chromosome was of maternal origin in eight patients and of paternal origin in two patients. Skewed XCI mosaicism could be considered as an important risk factor in scleroderma.

Chimerism occurs in thyroid, lung, skin and lymph nodes of women with sons

Chimerism indicates the presence of cells from one individual in another. Pregnancy and blood transfusions are considered the main sources for chimerism. Chimeric cells have been attributed a pathogenic role in various autoimmune diseases. However, data on the occurrence of chimeric cells in normal organs are scarce. In order to gain insight into the possible pathogenic potential of chimeric cells in autoimmune disease, it is necessary to determine the prevalence of chimeric cells in organs not affected by autoimmune disease. In situ hybridization for the Y-chromosome was performed on organs obtained at autopsy of 51 women. We investigated 44 thyroid, 38 lung, 21 skin and 7 lymph node samples. All women had sons, and data from their blood transfusion histories were retrieved for at least 10 years before death. Slides were scored semi-quantitatively for chimerism as low (1-3 Y-chromosome-positive cells per slide), moderate (4-10 positive cells per slide) or high (more than 10 positive cells per slide). Y-chromosome-positive cells were found in 8 thyroid, 10 lung, 3 skin and 1 lymph node samples of 18 women. There was no association between the presence of chimeric cells and blood transfusion history. Most organs in which chimerism was present contained a small to moderate level. Thus, chimerism can occur in normal organs of women without autoimmune disease. Our results indicate that chimerism is not necessarily associated with disease.

Persistence of fetal cells in the mother: friend or foe?

There is increasing evidence that both circulating cells and free fetal DNA persist in the maternal circulation after delivery of the fetus. In some cases, this has been described many years after the end of the pregnancy. This article reviews the evidence for these cells being present, the potential methodologies used to identify such cells and the potential effects on maternal immunomodulation. Data relating to the potential beneficial and potentially harmful effects are discussed.

The complex role of estrogens in inflammation

There is still an unresolved paradox with respect to the immunomodulating role of estrogens. On one side, we recognize inhibition of bone resorption and suppression of inflammation in several animal models of chronic inflammatory diseases. On the other hand, we realize the immunosupportive role of estrogens in trauma/sepsis and the proinflammatory effects in some chronic autoimmune diseases in humans. This review examines possible causes for this paradox. This review delineates how the effects of estrogens are dependent on criteria such as: 1) the immune stimulus (foreign antigens or autoantigens) and subsequent antigen-specific immune responses (e.g., T cell inhibited by estrogens vs. activation of B cell); 2) the cell types involved during different phases of the disease; 3) the target organ with its specific microenvironment; 4) timing of 17beta-estradiol administration in relation to the disease course (and the reproductive status of a woman); 5) the concentration of estrogens; 6) the variability in expression of estrogen receptor alpha and beta depending on the microenvironment and the cell type; and 7) intracellular metabolism of estrogens leading to important biologically active metabolites with quite different anti- and proinflammatory function. Also mentioned are systemic supersystems such as the hypothalamic-pituitary-adrenal axis, the sensory nervous system, and the sympathetic nervous system and how they are influenced by estrogens. This review reinforces the concept that estrogens have antiinflammatory but also proinflammatory roles depending on above-mentioned criteria. It also explains that a uniform concept as to the action of estrogens cannot be found for all inflammatory diseases due to the enormous variable responses of immune and repair systems.

Local and Circulating Microchimerism Is Associated with Hypersensitivity Pneumonitis

RATIONALE

Hypersensitivity pneumonitis (HP) is a lymphocytic alveolitis provoked by exposure to a variety of antigens. However, the disease occurs in only a subset of exposed individuals, suggesting that additional factors may be involved. Microchimerism has been implicated in the pathogenesis of autoimmune diseases, especially in those showing increased incidence after childbearing age.

OBJECTIVES

To evaluate the presence of circulating and local microchimeric cells in female patients with HP.

METHODS

Male microchimerism was examined in 103 patients with HP, 30 with idiopathic pulmonary fibrosis (IPF), and 43 healthy women. All of them had given birth to at least one son, with no twin siblings, blood transfusions, or transplants. Microchimerism was examined by dot blot hybridization (peripheral blood), and by fluorescence in situ hybridization in bronchoalveolar lavage cells and lungs.

MEASUREMENTS AND MAIN RESULTS

Blood microchimerism was found in 33% of the patients with HP in comparison with 10% in those with IPF (p = 0.019) and 16% in healthy women (p = 0.045). Patients with HP with microchimerism showed a significant reduction of diffusing capacity of carbon monoxide (Dl(CO); 53.5 +/- 11.9% vs. 65.2 +/- 19.7%; p = 0.02) compared with patients with HP without microchimerism. In bronchoalveolar lavage cells, microchimerism was detected in 9 of 14 patients with HP compared with 2 of 10 patients with IPF (p = 0.047). Cell sorting revealed that microchimeric cells were either macrophages or CD4+ or CD8+ T cells. Male microchimeric cells were also found in the five HP lungs examined by fluorescence in situ hybridization.

CONCLUSIONS

Our findings (1) demonstrate that patients with HP exhibit increased frequency of fetal microchimerism, (2) confirm the multilineage capacity of microchimeric cells, and (3) suggest that microchimeric cells may increase the severity of the disease.

Tissue chimerism in systemic lupus erythematosus is related to injury

BACKGROUND

Chimerism indicates the presence of cells from one individual in another individual, and has been associated with several autoimmune diseases. Although this finding may point towards a role for chimerism in the induction of SLE, it could also indicate that chimerism is the result of repair mechanisms after injury.

OBJECTIVE

To perform a post-mortem investigation for the presence of chimerism in 48 organs from seven women with SLE and establish whether there was a relationship between chimerism and injury.

METHODS

Chimeric male cells in female tissue specimens were identified by in situ hybridisation of the Y-chromosome. Organs were categorised into four different groups according to injury experienced.

RESULTS

were compared with those for unaffected control organs. Results: Chimerism was found in all seven patients with SLE. Y-chromosome-positive cells were present in 24 of 48 organs from women with SLE, which was significantly more than in control organs (p<0.001). Chimerism occurred more often in organs from patients with SLE who had experienced injury than in normal control organs, irrespective of whether the injury experienced was SLE-related, non-SLE-related or both.

CONCLUSIONS

This is the first report of the distribution of chimerism in a large number of organs from women with SLE. It shows that the occurrence of chimerism is related to injury. The data support the hypothesis that tissue chimerism is the result of a repair process.

Impact of fetal-maternal microchimerism on women's health--a review

Microchimerism is defined by the presence of circulating cells, bi-directionally transferred from one genetically distinct individual to another. It occurs either physiologically during pregnancy, or iatrogenically after blood transfusion and organ transplants. The migrated cells may persist for decades. Much controversy exists around the role of microchimeric cells in the pathogenesis of various diseases and around their role in tissue repair. Microchimerism has been investigated in different autoimmune disorders, such as systemic sclerosis, systemic lupus erythematosus, autoimmune thyroid diseases, primary biliary cirrhosis and juvenile inflammatory myopathies. Recent data have demonstrated the promising role of microchimeric cells in the maternal response to tissue injuries by differentiating into many lineages. Therefore, further understanding of fetal-maternal microchimerism may help in anticipating its implications in disease as well as in more general women's health issues.

Feto-maternal cell trafficking: a transfer of pregnancy associated progenitor cells

The embryonic and fetal development in the maternal uterine environment implies that different population of fetal progenitors must be in close contact to the maternal tissues. Accordingly, fetal mesenchymal and hematopoietic stem and progenitor cells have been described in the placenta and the fetal blood. Seeding in the maternal circulation, fetal progenitor cells can be detected in the circulation of pregnant women during most pregnancies. Decades after delivery, fetal CD34+ or mesenchymal stem cells are still detectable in maternal circulation or bone marrow. Recent studies point to the possibility for fetal progenitor cells persisting after pregnancy to home to maternal injured tissue and to adopt various phenotypes. Fetal cells in various maternal tissues can express epithelial, hepatocytic, hematopoietic, renal, cardiomyocytic, glial, or neuronal markers in human as well as mouse models. This apparent multipotency has been attributed to a fetal population of stem/progenitor cells acquired by the mother during pregnancy, named the pregnancy-associated progenitor cells. We will discuss the possible origins of this cell population and review the most recent data suggesting that these fetal microchimeric cells may participate in maternal tissue regeneration processes.

Maternal neoangiogenesis during pregnancy partly derives from fetal endothelial progenitor cells

Fetal progenitor cells enter the maternal circulation during pregnancy and can persist for decades. We aimed to determine the role of these cells in tissue inflammation during pregnancy. WT female mice were mated to males transgenic for the EGFP (ubiquitous) or the luciferase gene controlled by the VEGF receptor 2 (VEGFR2; V-Luc) promoter. A contact hypersensitivity reaction was triggered during such pregnancies. Fetal cells were tracked by using real-time quantitative amplification of the transgene (real-time PCR), Y chromosome in situ hybridization (FISH), immunofluorescence or in vivo bioluminescence imaging. Real-time PCR disclosed fetal cells in the inflamed areas in all tested mice (17/17) with higher frequency and numbers in the inflamed compared with the control areas (P = 0.01). Double labeling demonstrated CD31+ EGFP+ fetal cells organized as blood vessels. In WT pregnant mice bearing V-Luc fetuses, a specific luciferase activity signal could be detected at the hypersensitivity site only, demonstrating the elective presence of VEGFR2-expressing fetal cells. In conclusion, using various techniques, we found the presence of fetal endothelial cells lining blood vessels in maternal sites of inflammation. These results imply that fetal endothelial progenitor cells are acquired by the mother and participate in maternal angiogenesis during pregnancy.

Functional HY-Specific CD8+ T Cells Are Found in a High Proportion of Women Following Pregnancy with a Male Fetus1

Recent studies have demonstrated that fetal cells can be detected in the maternal circulation during virtually all human pregnancies. These fetal cells can engraft and may be isolated for many decades after pregnancy, leading to a state that may be maintained by the passage of pregnancy-associated progenitor cells. The clinical consequences of fetal cell microchimerism are unclear but may be potentially detrimental or valuable to the mother. One possibility is the generation of an alloreactive immune response by the mother to antigens expressed by the fetus; for example, the HY protein encoded by the Y chromosome. To test this we have screened a cohort of women with a range of parity histories within 8 yr of their last pregnancy for the presence of an HY-specific CD8+ T-cell response. Fluorescent HLA-peptide (HY) tetramers were used to stain short-term T-cell cultures from these women for analysis by flow cytometry. Responses were detected in 37% of women with a history of pregnancies that produced males, and this value rose to 50% in women with two or more pregnancies that produced males. HY-specific CD8+ T cells also could be detected directly in the peripheral blood of women with a history of at least two pregnancies that produced males. These HY-specific CD8+ T cells produced interferon gamma (IFNG) following peptide stimulation, demonstrating their functional capacity. In conclusion, our data indicate that alloreactive CD8+ T cells are generated frequently following normal pregnancy and retain functional capability for years following pregnancy.

Chimerism in systemic lupus erythematosus—three hypotheses

Systemic lupus erythematosus (SLE) is an immune-mediated disease characterized by the presence of autoantibodies and a wide array of clinical symptoms. Despite intensive research, the aetiology of SLE is still unknown and is probably multifactorial. Both genetic and environmental factors have been associated with SLE, but these factors alone are insufficient to explain the onset of SLE. Recently, it has been suggested that chimerism plays a role in the pathogenesis of autoimmune diseases, including SLE. Chimerism indicates the presence of cells from one individual in another individual. In an experimental mouse model, the injection of chimeric cells induces a lupus-like disease. In addition, chimerism is found more often in kidneys of women with SLE than in healthy controls. There are several mechanisms by which chimeric cells could be involved in the pathogenesis of SLE. In this review, three hypotheses on the role of chimerism in SLE are discussed. The first two hypotheses describe the possibilities that chimeric cells induce either a graft-vs-host reaction in the host (comparable with reactions seen after bone marrow transplantation) or a host-vs-graft reaction (comparable with reactions seen after solid organ transplantation). The third hypothesis discusses the possible beneficial role chimeric cells may play in repair mechanisms due to their stem cell-like properties. This review provides insights into the mechanisms by which chimerism may be involved in SLE and proposes several lines of inquiry to further investigate chimerism in SLE.

[Etiopathogenesis. New concepts]

Systemic sclerosis is a complex, progressive autoimmune disease. The origin is, so far, unknown and it is characterized by immunological and endothelial damage followed by fibrosis. Interaction between the host genetic backgrounds with environmental factors is thought to turn out an abnormal immune response characterized by clonal expansion of Th2 repertoire, upregulation of pro-fibrotic cytokines and dysregulated B cells. Specific autoantibodies profiles are associated with clinical subtypes of the diseases. Endothelial activation is an early feature with damage of the vasocontrictive and vasodilation response. Finally, persistent tissue ischemia and abnormal immune response produce myofibroblast proliferation andoverproduction of extracellular matrix proteins and fibrosis.

Association between microchimerism and multiple sclerosis in Canadian twins

Microchimerism, the persistence of foreign cells thought to derive from previous pregnancies, has been associated with autoimmune diseases. A maternal parent-of-origin effect in MS remains unexplained. We tested for microchimerism in monozygotic and dizygotic twin-pairs with MS. Microchimerism was associated with MS in affected females from monozygotic concordant pairs when compared to both affected (p=0.020) and unaffected (p=0.025) females in monozygotic discordant pairs. Microchimerism was increased in affected females of dizygotic discordant pairs (p=0.059). The rate of microchimerism was significantly higher in affected twins than in unaffected co-twins (p=0.0059). These observations show an association in twins between the presence of microchimerism and having MS.

Immunology of placentation in eutherian mammals

The traditional way to study the immunology of pregnancy follows the classical transplantation model, which views the fetus as an allograft. A more recent approach, which is the subject of this Review, focuses on the unique, local uterine immune response to the implanting placenta. This approach requires knowledge of placental structure and its variations in different species, as this greatly affects the type of immune response that is generated by the mother. At the implantation site, cells from the mother and the fetus intermingle during pregnancy. Unravelling what happens here is crucial to our understanding of why some human pregnancies are successful whereas others are not.

Pathophysiology of fetal microchimeric cells

Microchimerism has been defined by the presence of a low number of circulating cells transferred from one individual to another. The transfer of microchimeric cells naturally takes place during pregnancy and occurs bi-directionally between the mother and fetus. Further, microchimerism can also be a result of blood transfusions and organ transplants. Microchimeric cells have been implicated in health and disease. Fetal microchimerism has been correlated with the hyporesponsiveness of the maternal immune system towards a fetal allograft and with the longevity of organ transplants. However, microchimeric cells have been implicated in the pathogenesis of autoimmune diseases including systemic sclerosis. In contrast, microchimeric cells were found to contribute to tissue repair. Much controversy exists around the role of microchimeric cells in the pathogenesis of certain diseases, and these cells in tissues may be a consequence rather than the cause of disease.

Male microchimerism in women without sons: quantitative assessment and correlation with pregnancy history

PURPOSE

Fetal microchimerism, derived from fetal cells that persist after pregnancy, is usually evaluated by tests for male microchimerism in women who gave birth to sons. We investigated male microchimerism in women without sons and examined correlation with prior pregnancy history. Immunologic consequences of microchimerism are unknown. We studied healthy women and women with rheumatoid arthritis (RA).

METHODS

Y-chromosome-specific real-time quantitative polymerase chain reaction was used to test peripheral blood mononuclear cells of 120 women (49 healthy and 71 with RA). Results were expressed as the number of male cells that would be equivalent to the total amount of male DNA detected within a sample containing the equivalent of 100000 female cells.

RESULTS

Male microchimerism was found in 21% of women overall. Healthy women and women with RA did not significantly differ (24% vs 18%). Results ranged from the DNA equivalent of 0 to 20.7 male cells per 100000 female cells. Women were categorized into 4 groups according to pregnancy history. Group A had only daughters (n = 26), Group B had spontaneous abortions (n = 23), Group C had induced abortions (n = 23), and Group D were nulligravid (n = 48). Male microchimerism prevalence was significantly greater in Group C than other groups (8%, 22%, 57%, 10%, respectively). Levels were also significantly higher in the induced abortion group.

CONCLUSIONS

Male microchimerism was not infrequent in women without sons. Besides known pregnancies, other possible sources of male microchimerism include unrecognized spontaneous abortion, vanished male twin, an older brother transferred by the maternal circulation, or sexual intercourse. Male microchimerism was significantly more frequent and levels were higher in women with induced abortion than in women with other pregnancy histories. Further studies are needed to determine specific origins of male microchimerism in women.

Skewed X chromosome inactivation in blood cells of women with scleroderma

OBJECTIVE

Scleroderma (SSc) is an autoimmune disease of unknown etiology. The disease is 3-8 times more frequent in women than in men. The role of X chromosome inactivation (XCI) in the predisposition of women to autoimmunity has been questioned. Until now this has not been illustrated experimentally. This study was undertaken to test the hypothesis that disturbances in XCI mosaicism may be involved in the pathogenesis of the disease in female patients with SSc.

METHODS

Seventy female SSc patients and 160 female controls were analyzed for the androgen receptor locus by the Hpa II/polymerase chain reaction assay to assess XCI patterns in DNA extracted from peripheral blood cells. Furthermore, skin biopsy samples were obtained from 5 patients whose blood revealed an extremely skewed pattern of XCI, and the analysis repeated. Since microchimerism in SSc was reported, Y chromosome sequences were investigated in all samples.

RESULTS

Skewed XCI was observed in DNA from peripheral blood cells in 35 of 55 informative patients (64%), as compared with 10 of 124 informative controls (8%) (P < 0.0001). Extreme skewing was present in 27 of the patient group (49%), as compared with only 3 of the controls (2.4%) (P < 0.0001). However, XCI was random in all skin biopsy samples. The potential contribution of microchimerism to the random XCI pattern is highly unlikely based on the medical histories of the patients.

CONCLUSION

Skewed XCI mosaicism may play a significant role in the pathogenesis of SSc.

Multi-lineage potential of fetal cells in maternal tissue: a legacy in reverse

Fetal cells circulate in pregnant women and persist in blood and tissue for decades post-partum. The mother thus becomes chimeric. Factors that may influence such fetal cell microchimerism include histocompatibility, fetal or placental abnormalities, or a reproductive history that includes miscarriage or elective termination. Fetal cell microchimerism is associated with some maternal autoimmune diseases, such as systemic sclerosis. Moreover, a novel population of fetal cells, the pregnancy-associated progenitor cells (PAPCs), appears to differentiate in diseased or injured maternal tissue. The cellular origin of these cells is at present unknown but could be a hematopoietic stem cell, a mesenchymal stem cell, or a novel cell type. Pregnancy therefore results in the acquisition of cells with stem-cell-like properties that may influence maternal health post-partum. Rather than triggering disease, these cells may instead combat it.

Have recent immunogenetic investigations increased our understanding of disease mechanisms in the idiopathic inflammatory myopathies?

PURPOSE OF REVIEW

The idiopathic inflammatory myopathies (IIM) continue to provide a challenge given the variable effectiveness of the available treatments, and immunogenetic studies are ongoing to further elucidate IIM disease mechanisms. This review examines how recent research has improved our understanding of the mechanisms that lead to IIM.

RECENT FINDINGS

HLA-DRB1 studies in a large homogenous cohort of UK Caucasian patients have confirmed that polymyositis (PM) and dermatomyositis (DM) are not genetically identical diseases while other studies have shown that tumor necrosis factor alpha is genetically implicated in disease susceptibility. Some remarkable results from an international collaboration, correlating gene-environment interactions, clearly suggest that ultraviolet light is capable of modulating both clinical and immunologic features of IIMs. Studies on microchimerism are unraveling interesting associations in juvenile DM patients, and bolstering the hypothesis that myositis may be an 'allo-immune' disease. mRNA gene expression profiling is helping to increase our understanding of myositis pathogenesis, whilst animal models have provided new information on the roles of Th1 responses and nitric oxide synthase in muscle disease. New candidate genes have been examined in inclusion body myositis (IBM), and a novel gene transfer experiment has been conducted, which led to significant changes in expression of the IBM phenotype.

SUMMARY

Improving the understanding of the immunogenetics and immunopathogenesis of the IIMs may in the future provide novel therapeutic targets, and thus improve outcomes in these difficult diseases.

Microchimerism and systemic sclerosis

PURPOSE OF REVIEW

Although 6 years have elapsed since the initial report describing the presence of microchimeric cells in affected tissues from patients with systemic sclerosis, a mechanism by which these cells might contribute to the pathogenesis of the disease is still unknown. This article reviews the published literature related to the possible role of microchimeric cells in the pathogenesis of systemic sclerosis.

RECENT FINDINGS

Numerous studies have reported the identification or quantification of microchimeric cells in the peripheral blood or tissues from systemic sclerosis patients; however, only one study to date has investigated their function. Recent investigations have demonstrated microchimeric cells in the clinically uninvolved tissues from patients with systemic sclerosis, suggesting that these cells are present in early disease. However, after the identification of microchimeric cells in blood and tissues of patients with systemic sclerosis, these cells have been found in organs affected by nonautoimmune conditions. These cells are also commonly detected in the peripheral blood of healthy people.

SUMMARY

These observations have raised questions about whether microchimeric cells are responsible for the pathologic events in systemic sclerosis or are merely remnants of a pregnancy remote in time, and it has been suggested that they might also have beneficial effects for the host.

Fetomaternal cell traffic, pregnancy-associated progenitor cells, and autoimmune disease

Fetal cells in maternal blood are a potential source of fetal genetic material that can be obtained non-invasively. Efforts to isolate these cells from maternal peripheral blood are limited by their low circulating numbers (approximately 1 per ml of maternal blood in euploid pregnancies). Expansion of these cells by culture would provide more cells for diagnosis and give an opportunity to study fetal metaphase chromosomes. Despite extensive optimization of culture conditions, many groups have failed reproducibly to grow fetal cells from pre-procedural maternal samples. An unexpected benefit of this research has been the discovery of a novel population of fetal cells, the pregnancy-associated progenitor cell (PAPC), which remains in maternal blood and tissue for decades following delivery. These cells might play a role in some autoimmune diseases, such as scleroderma. PAPCs appear to have stem cell characteristics, such as the ability to proliferate and differentiate. Recently developed animal models will help to ascertain whether these cells cause disease, respond to disease, or have therapeutic applications.

Lack of evidence for leukocyte maternal microchimerism in primary biliary cirrhosis

AIM: It is reasonable to assume that microchimerism could also be involved in the induction of primary biliary cirrhosis (PBC). However, previous reports investigated only fetus-microchimerism in women patients. Maternal microchimerism has not been investigated until now. The current study aimed to clear either maternal microchimerism was involved in the pathogenesis of PBC or not.

METHODS: We used fluorescence in situ hybridization on paraffin-embedded tissue (We called “Tissue-FISH”.) to determine whether maternal cells infiltrated in male patients who were diagnosed as having PBC. Tissue-FISH was performed by using both X and Y specific probes on the biopsy liver sample of 3 male PBC patients.

RESULTS: Infiltrating lymphocytes demonstrated both X and Y signals in all 3 male patients.

CONCLUSION: Maternal microchimerism dose not play a significant role in PBC. PBC may not relate to fetus and maternal microchimerism.

Does HLA-Dependent Chimerism Underlie the Pathogenesis of Juvenile Dermatomyositis?

Juvenile dermatomyositis (JDM) is a multisystem autoimmune disease that at times resembles chronic graft-vs-host disease. This led us to suggest that nonself cells may play a role in the disease process. In this study we examined the relationship between HLA genotype and the presence of maternally derived chimeric cells in JDM patients and healthy controls, and assessed immunologic activity in the chimeric cells. We identified chimeric cells more often in children with JDM (60 of 72) than in their unaffected siblings (11 of 48) or in healthy controls (5 of 29). The presence of chimerism in the JDM patients, their healthy siblings, and unaffected control children was associated with a HLA-DQA1*0501 allele in the mother (p = 0.011). Further, we show that maternally transferred chimeric T cells are responsive to the host's (JDM childs') lymphocytes (33.75 +/- 8.4 IFN-gamma-producing cells from JDM cells vs 5.0 +/- 1.25 from maternal cells), and that this is a memory response. These combined data indicate that chimeric cells play a direct role in the JDM disease process and that the mother's HLA genotype facilitates the transfer and/or persistence of maternal cells in the fetal circulation.

The assessment and importance of disease activity versus disease damage in patients with inflammatory myopathy

To capture the totality of the effect of a disease on a patient, three aspects of the disease need to be assessed: 1) the disease activity (which is potentially reversible with treatment); 2) damage (defined as irreversible changes in anatomy, physiology, or function) accumulated since the onset of the disease, albeit from the disease itself, comorbid conditions, or as a result of therapy; and 3) the patient's perception of the disease, because this is frequently different from the physician's perception. A fine line exists between under-treating a patient, which may lead to an increase in disease activity, and over- treating a patient, with the risk of serious morbidity from inappropriate therapy. Distinguishing between activity and damage can be difficult and measures to ascertain this are discussed. Further developments are underway to assess the measures that should be used for the assessment of disease activity and damage.