No abstract

Objective. HLA-DRB1 alleles associated with risk of rheumatoid arthritis (RA) encode similar HLA-DRB1 sequences, called the shared epitope (SE). The most common SE sequences are QKRAA and QRRAA. Nevertheless, a substantial number of RA patients lack the SE. Bidirectional fetal-maternal trafficking results in long-term persistence of fetal cells in the mother and maternal cells in her offspring, a process known as microchimerism. This study was undertaken to discover whether RA patients who lack the SE can acquire it through microchimerism.Methods. We studied a total of 86 female subjects who were genotypically negative for the SE, comprising 52 patients with RA and 34 healthy controls. We developed specific real-time quantitative polymerase chain reaction assays for the SE-encoded sequences QKRAA and QRRAA, and used them to test DNA extracted from peripheral blood mononuclear cells.Results. Microchimerism with the SE was found significantly more often in RA patients than controls (odds ratio 4.1 [95% confidence interval 1.6-10.0], P ‫؍‬ 0.003). Concentrations of SE microchimerism were also significantly higher among RA patients than controls (P ‫؍‬ 0.002). In separate analyses for SE type, the prevalence of QKRAA microchimerism in RA patients versus healthy controls was 17% versus 3% (9 of 52 versus 1 of 34; P ‫؍‬ 0.03) and the prevalence of QRRAA microchimerism was 40% versus 18% (21 of 52 versus 6 of 34; P ‫؍‬ 0.04), respectively. Microchimerism concentrations were also higher in RA patients than healthy subjects for QKRAA (P ‫؍‬ 0.03) and QRRAA (P ‫؍‬ 0.03).Conclusion. These results indicate that RA patients who genotypically lack the SE can acquire the SE as persistent microchimerism from fetal-maternal cell exchange, suggesting that SE-encoding microchimerism could be a risk factor for RA.

Previous studies have shown elevated concentrations of free fetal deoxyribonucleic acid and erythroblasts in maternal circulation in preeclampsia compared with normal pregnancy. Pluripotent and immunocompetent fetal cells also transfer to the maternal circulation during pregnancy, but whether concentrations of fetal mononuclear cells also differed in preeclampsia was unknown. We sought to quantify cellular fetal microchimerism in maternal circulation in women with preeclampsia and healthy controls. We studied women with preeclampsia and compared them with women with healthy pregnancies at similar gestational age. To identify a targetable polymorphism unique to the fetus to quantify fetal microchimerism, participants and family members were genotyped for the Human Leukocyte Antigen loci DRB1, DQA1, and DQB1, as well as several other polymorphisms. A panel of polymorphism-specific quantitative polymerase chain reaction assays was employed to identify and quantify fetal microchimerism in maternal peripheral blood mononuclear cells. Of 53 preeclampsia samples tested for cellular fetal microchimerism, 17 (32%) were positive, compared with 6 of 57 (6%) control samples (unadjusted odds ratio for detection 4.0, 95% confidence interval 1.5 – 11.1, p=0.007). The concentration of cellular fetal microchimerism (expressed as genome equivalents of fetal microchimerism per 100,000 maternal genome equivalents) was also higher among women with preeclampsia: median 0.0, mean 5.7, range 0-153.7, compared with controls: median 0.0, mean 0.3, range 0-9.1, p=0.002. We conclude that women with preeclampsia harbor cellular fetal microchimerism more commonly and at higher concentrations compared with women with uncomplicated pregnancy. The functional capacity and phenotype of these fetal cells is not yet known.

Objective Cell trafficking during pregnancy results in persistence of small populations of fetal cells in the mother, known as fetal microchimerism (FMc). Changes in cell-free fetal DNA during gestation have been well-described, however, less is known about dynamic changes in fetal immune cells in maternal blood. We investigated FMc in maternal peripheral blood mononuclear cells (PBMC) longitudinally across gestation. Study Design Thirty-five women with normal pregnancies were studied. FMc was identified in PBMC, CD4+ and CD8+ subsets employing quantitative PCR assays targeting fetal-specific genetic polymorphisms. FMc quantities were reported as fetal genome equivalents (gEq) per 1,000,000 gEq mother’s cells. Poisson regression modeled the rate of FMc detection. Main Outcome Measure FMc in PBMC Results The probability of detecting one fetal cell equivalent increased 6.2-fold each trimester [Incidence Rate Ratio (IRR) 95% CI: 1.73, 21.91; p=0.005]. Although FMC in PBMC was not detected for the majority of time points, 7 of 35 women had detectable FMc during pregnancy at one or more time points, with the majority of positive samples being from the third trimester. There was a suggestion of greater HLA-sharing in families where women had FMc in PBMC. FMc was detected in 9% of CD4+ (2/23) and 18% of CD8+ (3/25) subsets. Conclusions FMc in PBMC increased as gestation progressed and was found within CD4+ and CD8+ subsets in some women in the latter half of gestation. A number of factors could influence cellular FMc levels including subclinical fetal-maternal interface changes and events related to parturition. Whether FMc during pregnancy predicts persistent FMc and/or correlates with fetal-maternal HLA-relationships also merits further study.