Detection of microchimeric cells in the peripheral blood of nonpregnant women is enhanced by magnetic cell sorting before PCR

Comparison of different blood sample processing methods for sensitive detection of low level chimerism by RHD real-time PCR assay

The rhesus D blood group, which is expressed on the red blood cells (RBC) of 85% of the Caucasian population, is one of the most immunogenic RBC antigens, inducing D antibody formation in up to 20-80% of D-negative transfusion recipients and about 10% of pregnancies at risk. Pregnancy-induced D-antibodies can persist for many years, but the mechanisms underlying this persistence are unclear. The LOTUS study, a long-term follow-up study of mothers from severely affected children with hemolytic disease of the fetus and newborn investigates, among other endpoints, whether persistent feto-maternal chimerism is associated with long-term maternal anti-D persistence. We questioned which blood sample processing method should be used to detect low levels of RHD chimerism with the highest sensitivity and specificity using qPCR. After optimization of primer and probe concentrations for singleplex RHD exon 5 and 7 qPCR, sensitivity, specificity and efficiency of RHD and DYS1 qPCR were investigated in artificial chimeric samples. Sensitivity of DYS1 was one log higher (0.0001%) in enriched mononuclear cell fractions as compared with whole blood. Comparable linear sensitivity (0.007%) and mean efficiency (84-99%) for RHD qPCR were observed in all samples regardless whether whole blood or pre- or post-mixing of cellular fractions had been used. We conclude that RHD chimerism using singleplex exon 5 and 7 qPCR is linearly detectable down to 1.0 GE, without an advantage of fraction enrichment.

Maternal microchimerism protects against the development of asthma

BACKGROUND

Maternal asthma and child's sex are among the most significant and reproducible risk factors for the development of asthma. Although the mechanisms for these effects are unknown, they likely involve nonclassical genetic mechanisms. One such mechanism could involve the transfer and persistence of maternal cells to her offspring, a common occurrence known as maternal microchimerism (MMc). MMc has been associated with many autoimmune diseases but has not been investigated for a role in asthma or allergic disease.

OBJECTIVE

We hypothesized that some of the observed risks for asthma may be due to different rates of transmission or persistence of maternal cells to children of mothers with asthma compared with children of mothers without asthma, or to sons compared with daughters. We further hypothesized that rates of MMc differ between children with and without asthma.

METHODS

We tested these hypotheses in 317 subjects from 3 independent cohorts by using a real-time quantitative PCR assay to detect a noninherited HLA allele in the child.

RESULTS

MMc was detected in 20.5% of the subjects (range 16.8%-27.1% in the 3 cohorts). We observed lower rates of asthma among MMc-positive subjects than among MMc-negative subjects (odds ratio, 0.38; 95% CI, 0.19-0.79; P = .029). Neither maternal asthma nor sex of the child was a significant predictor of MMc in the child (P = .81 and .15, respectively).

CONCLUSIONS

Our results suggest for the first time that MMc may protect against the development of asthma.

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.

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.

HLA-DQA1 is not an apparent risk factor for microchimerism in patients with various autoimmune diseases and in healthy individuals

OBJECTIVE

Microchimeric cells have been identified in lesions and peripheral blood of patients with systemic sclerosis (SSc) and idiopathic inflammatory myopathies (IIM), and HLA-DQA1*0501 is a risk factor for these diseases in some populations. Furthermore, DQA1*0501 has been associated with T lymphocyte microchimerism in SSc. To better define the strength of this association, we assessed the relationship among DQA1 alleles and microchimerism.

METHODS

DNA from whole peripheral blood or magnetically sorted T cells was tested for microchimeric cells by polymerase chain reaction of the Y chromosome or of HLA-Cw in 87 SSc patients, 28 juvenile IIM patients, and 88 healthy controls. Thirty-seven mother-son pairs were also analyzed for microchimerism and DQA1*0501.

RESULTS

We were unable to demonstrate that DQA1*0501 is associated with microchimerism in T lymphocytes or in whole peripheral blood DNA in patients with SSc or juvenile IIM or in healthy individuals. In the 37 mother-son pairs, we were unable to demonstrate an association of DQA1*0501 with microchimerism in peripheral blood DNA or T lymphocytes, and compatibility between the donor's and recipient's HLA alleles did not influence microchimerism in the recipient.

CONCLUSION

These data suggest that HLA-DQA1 alleles do not appear to play a role in the persistence of microchimerism in the peripheral blood or T lymphocytes of patients with selected autoimmune diseases or in healthy individuals.

Microchimerism and scleroderma: an update

Microchimerism has been defined by the presence of a low number of circulating cells transferred from one individual to another. This transfer takes place naturally during pregnancy, between mother and fetus, or between fetuses in multigestational pregnancies. Furthermore, the establishment of microchimerism can also occur during blood transfusion, as well as during bone marrow and solid-organ transplants. Recently, microchimeric cells have been implicated in the pathogenesis of autoimmune diseases, particularly systemic sclerosis. Studies have demonstrated an increased presence of microchimeric cells in peripheral blood and tissues from patients with systemic sclerosis, and, more recently, microchimeric cells were demonstrated to be specifically activated and capable of recognizing patient human leukocyte antigens.