The pathogenetic mechanisms of autoimmune diseases such as systemic sclerosis, in which the body "attacks" its own tissues, are not fully understood. Environmental, infective or hormonal factors may be involved in triggering scleroderma. Recently (1997) researchers postulated that microchimerism might be another pathogenetic mechanism in systemic sclerosis.

Chimerism is a condition in which cells from another individual are present in the blood of a person and are tolerated by his immune system. Bone marrow transplant in patients with haematological diseases is an example of chimerism in the recipient. We talk about microchimerism when the number of foreign cells is small. Several mechanisms may contribute to microchimerism, including maternal-to-foetal transmission, foetal-to-maternal transmission, twin-to-twin transmission and sexual transmission. Foetal cells have been found to persist in maternal peripheral blood for decades after childbirth. Researchers from Boston discovered that cells from a foetus can survive in a woman for up to 27 years after pregnancy.

Scleroderma has a predilection for women with an increased incidence following the childbearing years. Also, chronic graft-versus-host disease, a condition of chimerism that can occur after bone marrow transplant, has many clinical similarities to scleroderma. Microchimerism seems to be more common in scleroderma than in the healthy population. Male DNA has been found in many women with scleroderma, in peripheral blood and in the skin, but is very rare in healthy females. These observations led to the hypothesis that microchimerism is involved in the pathogenesis of autoimmune diseases such as scleroderma. Researchers suggest that persisting foetal cells may at some point become activated by external factors such as viruses, chemicals, radiation or drugs. This reaction disrupts the host’s immune system and initiates an immunological attack against the body’s own tissues.

There are, however, some unresolved questions: scleroderma is not exclusively a disease of women. It still needs to be explained why scleroderma occurs in men and in women who have never given birth. It has been suggested that transfer of maternal cells to the foetus, which then persist into adulthood, could explain it. In fact maternal cells have been found in male scleroderma patients. At the moment, the existing data are not strong enough to prove whether microchimerism has a role in the pathogenesis of systemic sclerosis and more research has to be done in this area.

Dr Magdalena Dziadzio
April 03