microchimerism is defined as the presence of low concentrations of two genetically distinct cell populations in the same individual . it can arise from several causes including the bidirectional transfer of cells between mother and fetus during pregnancy , twin - to - twin transfer in utero , from organ transplantation , and blood transfusion . recently , there has been increasing interest in fetomaternal microchimerism as it relates to real or potential health implications in autoimmune diseases , graft - versus - host reactions , and transfusion complications ( see figure 1 ) . we now know that the placenta is not an immunologically inert barrier , but rather , it allows the reciprocal transport of maternal and fetal cells in a state of mutual tolerance during gestation . to develop microchimerism , it is not necessary to continue a pregnancy and deliver an infant . early terminations from surgical abortion can deliver up to 500,000 nucleated fetal cells into a woman 's circulation . fetal microchimerism in maternal blood and tissues is typically identified using polymerase chain reaction ( pcr ) to identify y - chromosome dna sequences in the mother . microchimerism does not require the fetus to be male , but it is easier to distinguish the y chromosome as a biomarker . interestingly , male microchimerism has been found in a fifth of women with no male births . this can occur in a number of ways including early miscarriage of a male embryo , a vanished male twin , male cell transfer from an older sibling through the maternal circulation to a later pregnancy , or a yet unexplored possibility , that of male dna transferred to the woman 's circulation from sexual intercourse . , a woman confronts an immunological challenge , because the fetus carries paternal genes , some of which are expressed on the cell surface and may provoke potent allogeneic responses . yet , in spite of these immunologic cell differences , rejection of the fetus does not frequently occur . the major histocompatibility complex ( mhc ) is the body 's antiviral spyware program that resides on chromosome 6 . the mhc contains genes that are involved in recognizing self from nonself and include human leukocyte antigen genes ( hla ) . the hla system contains over 200 genes , 40 of which are involved with encoding leukocyte antigens . class i antigens ( a , b , and c ) present antigens that invade cells ; class ii antigens ( dr , dp , and dq ) present antigens , so t - lymphocytes can determine if they should help b - cells make more antibody to a particular antigen . the hla genes tend to be inherited as a group , one from the mother and one from the father . the proteins encoded by hla are the proteins on the outer part of body cells that are unique to a person . the hla system is involved with such diverse clinical conditions as organ rejection in transplantation , death from infection in immunodeficiency , hepatic cirrhosis caused from iron overload , and autoimmune diseases . this is the reason why donors are matched at major histocompatibility alleles ( hla - a , b , dr ) in stem - cell transplantations . yet , minor histocompatibility antigens such as h - y antigen may play a bit more havoc in disease and transplant rejection than was previously thought .    in the genetically male fetus , the y chromosome contains a gene that codes for a protein called h - y antigen . when h - y antigen secretion begins , the primordial gonads become testes .   without a y chromosome , there is no h - y protein , and the primordial gonads become ovaries . h - y is a minor histocompatibility antigen present on all male cells that is widely conserved in evolution . it has been detected in cells from every mammalian species tested . the gene for the h - y antigen is located on the short arm of the y chromosome . males develop tolerance to these self antigens , but female t cells are capable of recognizing peptides derived from h - y proteins following transplantation . sex - mismatched transplantations can result in major activation of the immune system even in the face of hla - identical allografts . the risk of rejection is far greater with male solid organ grafts into female recipients . although the exchange of fetal maternal cells is common with all pregnancies , there appears to be increased levels of immune complexes in the serum of newborn males than in newborn females . this may occur because women who have delivered male offspring can produce antibodies to h - y proteins . in subsequent pregnancies with males , those antibodies can cross the placenta and react with circulating h - y antigen and form immune complexes . one of the factors that increase graft - versus - host disease in allogeneic stem - cell transplantation is the use of multiparous females as donors . it has been reported that male fetal progenitor cells have been detected as long as 27 years postpartum . this phenomenon , however , is not evident in all women nor is it evident in all male offspring . findings from a london hospital - based study revealed that women who developed cytotoxic antibodies during their first pregnancy had significantly more male infants , suggesting that the male fetus is more strongly antigenic than the female . secondly , they noted that in women with antibodies , the proportion of male births lessened as parity increased implying that once sensitization takes place , antibody or some related factor operates selectively in favor of the female fetus . fetomaternal red cell alloimmunization , a condition that affects one in a thousand pregnancies , involves male predominance among d+ infants who stimulate alloimmunizations in their d - mothers . the male infants have lower hemoglobin and hematocrit values and require more intrauterine , intravascular transfusions .   about 80% of all people with autoimmune diseases are women . several hypotheses have been proposed to explain the reasons for the gender difference such as hormones or stronger immune responses in women . progressive systemic sclerosis ( pss ) , also known as scleroderma , is an autoimmune disease that primarily affects women in their postpartum years and bears a striking resemblance to graft - versus - host disease . its clinical manifestation can cause damage to the liver , gastrointestinal tract , skin , and mucosa among other bodily systems . it also resembles a number of spontaneously occurring autoimmune diseases including , sjogren 's syndrome , primary biliary cirrhosis , and system lupus erythematous . researchers have begun looking at the association of microchimerism in certain autoimmune diseases that primarily affect women . the first study that investigated naturally acquired microchimerism in autoimmune disease was a prospective , blinded study of fetal microchimerism in women with pss . the study used a quantitative assay to test for male dna in women with pss and healthy women who had given birth to at least one son . some women with pss who had given birth to a male infant decades earlier had results equal to the highest quartile of the assay used to test women currently pregnant with a healthy male fetus . male dna was found 1 to 27 years after childbirth in six to eight women with pss who had sons . likewise , women with pss who had given birth to at least one son had larger amounts of male dna than healthy women and had extractable male dna in skin lesions    .   these findings ushered in a spate of studies suggesting that because most autoimmune diseases occurred in women , perhaps fetal cells played a role . although many of these studies have noted the presence of male fetal cells in women with the disease , often times similar finding were found in control groups . for example , a study of 22 women with systemic lupus erythematosus ( sle ) and a healthy control group found no difference in the amount or prevalence of male fetal cells . male microchimeric cells were found equally in 50 percent of the women in the patient group and 50 percent in the control group . yet , patients with a history of lupus nephritis had a higher mean number of fetal cells than patients with no such history . hashimoto 's thyroiditis is an autoimmune disease believed to be the most common cause of primary hypothyroidism . it occurs primarily in women between the ages of 45 to 65 and has a range of symptoms including weight gain , depression , fatigue , mania , memory loss , panic attacks , and hair loss . using thyroid gland specimens from 21 hashimoto thyroiditis patients , 18 patients with multinodular goiter , and 17 women with normal thyroid glands ( autopsy specimens ) , investigators found y chromosome dna in 8 of the 21 women with hashimoto 's disease , 1 in 18 women from the multinodular group , and none of 17 healthy thyroid glands . sjogren 's syndrome is an autoimmune disease characterized by dry mouth and dry eyes that can affect other parts of the body as well . fetal microchimerism was the focus in a study of 56 women with sjogren 's syndrome , 42 of them had at least one male child . each subject had her peripheral blood , labial salivary gland , and bronchoalveolar fluids sampled . male dna was shown to exist in 29% of salivary glands and 22% of lung specimens in female patients with sjogren 's . four of the subjects who were more than 60 years old had detectable fetal cells in their peripheral blood up to 27 years postpartum . one subject who tested positive for male dna did not have a male child or a history of abortion . she did , however , have a history of blood transfusion five years before the study . it is likely the male dna was derived from one or more transfusions in her past . examples of autoimmune diseases where fetal y - chromosomes were detected decades after pregnancy : 
 progressive systemic sclerosis , hashimoto 's thyroiditis , systemic lupus erythematosus , sjogren 's syndrome . progressive systemic sclerosis , hashimoto 's thyroiditis , systemic lupus erythematosus , sjogren 's syndrome . progressive systemic sclerosis , hashimoto 's thyroiditis , systemic lupus erythematosus , microchimerism from nonleukoreduced cellular blood products has been found to persist from months to years after transfusion . it was previously shown that in trauma patients given at least two units of nonleukoreduced red blood cells , donor leukocytes would decline markedly for the first 3  days after transfusion only to increase tenfold on day 4 followed by a secondary decline of donor cells from days 5 to 7 . a subsequent study found that half of the trauma patients who received leukoreduced blood transfusions had detectable microchimeric cell populations for 2 to 3  years after transfusion . of the characteristics investigated that might explain the persistent microchimerism , only the age of the transfused unit was correlated . transfusion - related acute lung injury ( trali ) is the most frequent cause of death from blood and blood - derived products in the us . it is widely accepted that the transfusion - related reaction likely results from an antigen antibody reactivity between the donor 's plasma and the recipient 's blood cells or vice versa . the antibodies recognize targets on the recipient 's white blood cells including hla class i and ii antigens . pregnancies are thought to be the major source of alloantibodies although prior donor transfusions may also play a role .   in two cases presented by french physicians the recipients developed strong alloantibodies against hla class i and ii antigens that were present on the somatic cells of the donors ' husbands and shared by the respective recipients . typing the husbands proved useful in identifying the specificity involved in the trali . just as a sex - mismatched hla - identical solid organ transplant from male to female can end in rejection , a similar interaction may be responsible for trali reactions with multiparous donors who have been pregnant with sons and are , therefore , microchimeric for h - y antigen . the research into microchimerism , and more specifically fetomaternal microchimerism , is still in its infancy . the literature has not progressed significantly beyond a speculative role for the long - term existence of fetal cells in women with autoimmune diseases . the jury is still out as to the relationship that fetomaternal microchimerism may play in disease . since nearly all of the studies found a significant level of normal females with microchimerism , some researchers have suggested that microchimeric cell populations that occur as a result of pregnancy may have stem - cell - like properties that can home in on damaged organs and tissues and differentiate as part of the maternal repair response .     just as cardiovascular diseases displaced infectious illnesses with the introduction of penicillin in the 1950s , genetically derived disorders are now among the most widespread afflictions confronting contemporary society . as genetic testing becomes an integral part of patient care , nurses will be needed to provide education , counseling , and followup services . new genetic discoveries will spawn a need to rethink the nursing paradigm as it relates to education , practice , and research . as knowledge of microchimerism and other genetically based illnesses expands , nurses will be confronted with how to manage the new information and challenges it will bring .
microchimerism is 
                   defined as the presence of two genetically 
                   distinct cell populations in the same 
                   individual . 
 it can arise from several causes 
                   including the bidirectional transfer of cells 
                   between mother and fetus during pregnancy , twin - to - twin transfer in utero , from organ 
                   transplantation , and blood transfusion . 
 recently , scientists have found male fetal cells 
                   from decades earlier imbedded in tissues and 
                   organs of some women with autoimmune diseases . 
 the significance of these findings as they 
                   relate to real or potential health implications 
                   in autoimmune diseases , graft - versus - host 
                   reactions , and transfusion complications is 
                   discussed here .