Chimerism in scleroderma

Feto-maternal microchimerism in connective tissue diseases

Fetal progenitor cells traffic to the mother during pregnancy and can persist in the maternal circulation for many years. Feto-maternal microchimerism has been reported in women with scleroderma, but its contribution to the disease pathogenesis remains unclear. Furthermore, the involvement of microchimerism in other connective tissue diseases is controversial. We studied 243 females, 122 of whom had previously carried a male fetus (50 healthy controls, 23 patients with scleroderma, and 49 with other connective tissue diseases). The presence of the male-specific SRY sequence was analyzed using a kinetic quantitative ELISA PCR assay that allows detection of one to three male cells in one million female cells. The percentage of SRY-positive samples was not different among women having borne son(s): 16% (95% confidence interval 0.07-0.29) in healthy controls, 21.7% (0.07-0.44) in patients with scleroderma and 25.5% (0.14-0.40) in patients with connective tissue diseases (p=0.25). The mean number of fetal cells was similar in the three groups. Among the 121 females who never carried a male fetus, no healthy woman was SRY positive. However, 33% of patients with scleroderma and 22.9% of women with connective tissue diseases were chimeric, a phenomenon which might be related to early miscarriage(s). Therefore, feto-maternal microchimerism is a common event in both healthy controls and patients with connective tissue diseases, and is unlikely to represent per se a risk factor for these diseases.

Microchimerism and scleroderma

It is now known that cells traffic between fetus and mother during normal human pregnancy. Moreover, fetal cells have been found to persist in the maternal peripheral blood for decades after childbirth. Chronic graft-versus-host disease, a known condition of chimerism that occurs after allogeneic hematopoietic stem cell transplantation has clinical similarities to some autoimmune diseases, including scleroderma (SSc). SSc has a predilection for women and an increased incidence in women following childbearing years. These observations when considered together with the longterm persistence of fetal cells led to the hypothesis that microchimerism is involved in autoimmune diseases such as SSc. Initial studies of women with SSc lend support to the hypothesis. Microchimerism, however, is also very common in healthy normals, and available data is not sufficient to be conclusive with respect to disease pathogenesis. Microchimerism can also occur due to engraftment from a blood transfusion, from a twin, or from the mother, sources that are applicable to men and women who have never been pregnant. The mechanism(s) by which microchimerism might contribute to SSc are not known, although some insight may be gained from studies of chimerism in transplantation biology. If microchimerism does contribute to the pathogenesis of autoimmune disorders such as SSc, it is likely that new therapeutic strategies could be developed.

Microchimerism: implications for autoimmune disease

Recent studies indicate cells traffic between the fetus and mother during normal human pregnancy and that fetal cells persist in maternal peripheral blood for decades after childbirth. The long-term persistence of fetal cells, when considered together with clinical similarities of chronic graft-vs-host disease and autoimmune disease and the female predilection to autoimmunity, led to the hypothesis that microchimerism is involved in some autoimmune diseases. Sources of engraftment applicable to men and to women who have never been pregnant include from a blood transfusion, a twin sibling, or mother. Initial studies lend support to the hypothesis. A role in disease pathogenesis has not been demonstrated, however, and microchimerism is also common in healthy normals. If microchimerism is involved in the pathogenesis of some autoimmune diseases further understanding potentially may lead to new therapeutic strategies.