[Microchimerism in scleroderma: ten years later]

More than ten years ago, the hypothesis that foetal microchimerism (Mc), arising from pregnancy, may have a reaction against the host, or "auto/allo"-immune reaction, has been proposed. More frequent and quantitatively larger foetal Mc found in blood from women with systemic sclerosis (SSc), compared to matched healthy women, argued this hypothesis. Since, Mc has been investigated in SSc and many diseases; however, results were often contradictory. Several explanations are discussed in the current review to understand the controversy and reveal interesting points. Ten years of research allowed to understand that a microchimeric cell is capable of the worst as well as the best depending upon specific factors (environmental, genetics...). Reversion to a non-aggressive phenotype seems possible and gives therapeutic hope.