Male microchimerism in healthy women and women with scleroderma: cells or circulating DNA? A quantitative answer

Male DNA, of presumed fetal origin, can be detected in the maternal circulation decades after delivery and is referred to as fetal microchimerism (FM). We previously found quantitatively greater FM in the circulation of women with the autoimmune disease scleroderma (SSc) than of healthy women. However, it is unknown whether this difference is due to intact circulating cells or free DNA released from breakdown in disease-affected tissues. To distinguish the origin of FM, we developed a real-time quantitative polymerase chain reaction (PCR) assay for the Y-chromosome-specific sequence DYS14, and tested 114 women in peripheral blood mononuclear cells (PBMCs) and/or plasma. Fifty-seven controls and 57 SSc patients were studied, 48 and 43 of whom, respectively, had given birth to at least one son. Circulating FM was quantitatively greater in PBMCs from SSc patients (n = 39; range, 0.0-12.5 male genome-equivalent cells per million maternal cells), compared with healthy women (n = 39; range, 0.0-4.4; P =.03). In contrast, there was no difference between patients (n = 25) and controls (n = 22) in plasma, and no evidence of free DNA. FM was enriched among T lymphocytes compared with PBMCs (P =.01) in controls (n = 14), but not in SSc patients (n = 14); the latter finding was most likely due to immunosuppressive medications. In conclusion, this real-time quantitative assay showed that quantitative differences in the circulation of women with SSc are due to cells and not to free DNA. As FM was not uncommon in healthy women, including among T cells, and because graft-versus-host disease has similarities to SSc, these results also suggest that FM merits investigation in pheresis products used for stem cell transplantation.