more sophisticated understanding of the evolution and expression of sexual dimorphism.Box 2. Microchimerism and DiseaseAs a result of bi-directional cell trafficking between the mother and fetus during pregnancy, mothers may harbor cells from their children and children may harbor cells from their mother will into adulthood. This mixture of a small amount of cells from a genetically disparate individual is referred to as microchimerism107. The persistence of maternal cells in her children, called maternal microchimerism, has been detected in the peripheral blood mononuclear cells in approximately 22% of healthy individuals108-111. The persistence of fetal cells in the mother is called fetal microchimerism, which has been detected in peripheral blood mononuclear cells in 30% to 55% of healthy women, depending on the outcome of the pregnancy112. Maternal microchimerism is found less often than fetal microchimerism in unselected peripheral blood mononuclear cells as well as in cellular subsets, such as T and B lymphocytes, monocyte/macrophages, and natural killer cells113. Moreover, microchimerism has been found in many human tissues and has the capacity to differentiate into tissue-specific cells, including myocytes, hepatocytes, and other cell types114-116. While some studies have reported differences in the prevalence of microchimerism between healthy individuals and patients with autoimmune
