Leader Non-Host Cells in the Pathogenesis of Autoimmune Disease

518 Ann Rheum Dis 1999;58:518–520 Leader Ann Rheum Dis: first published as 10.1136/ard.58.9.518 on 1 September 1999. Downloaded from Non-host cells in the pathogenesis of autoimmune disease: a new paradigm? Autoimmune diseases are thought of as disorders in which healthy women. Women were selected who had given birth a body’s cells inexplicably attack its own tissues. Usually to at least one son and a quantitative direct polymerase there is little evidence that anything is abnormal in the chain reaction (PCR) assay was used to test for a body tissues before the immunological attack begins. Y-chromosome specific sequence. Sons were studied for Drawing together observations from unrelated fields of technical reasons because of the ability to detect male medicine and science, microchimerism has been proposed DNA in a female host. (In contrast with the erroneous as a new consideration in the pathogenesis of some statement of an accompanying editorial, nested PCR was autoimmune disorders.1 The term chimerism is used to not used in any assay). Male DNA was found more indicate a body that contains cell populations derived from frequently and at quantitatively greater levels in women diVerent individuals and microchimerism refers to low lev- with SSc compared with healthy women.11 Among 16 els of non-host cells. The observations draw from healthy women the range of male cell equivalents was 0 to pregnancy immunology, transplantation biology, prenatal 2, mean 0.38. In contrast, women with SSc had a range of diagnostics, and autoimmunity. The key observation that 0 to 61 male cell equivalents, mean 11.1 (table 1). The dif- led to the proposal came from investigators working to ference between the two groups was statistically significant, establish sensitive techniques for prenatal diagnosis. As a p=0.0007. Some women with SSc had levels of male DNA result of the application of molecular techniques to pre- that were higher than that found in most women who are natal diagnosis it is now known that fetal cells enter the currently pregnant with a normal male fetus, although the mother’s blood early in the course of most pregnancies. In patients had given birth to their sons decades previously. 1996 a report by Dr Diana Bianchi and colleagues cast a The study was blinded for all identifying information potentially new stage for the well recognised female including patient versus control and reproductive charac- predominance of autoimmunity disease. The investigators teristics. This observation was extended in a study that found that fetal cells also persist in the maternal circulation examined microchimerism in the skin of patients with for decades after pregnancy completion.2 Long term Ssc.12 The study was retrospective, used a nested PCR persistence of fetal cells, when considered together with assay for a Y-chromosome specific sequence, and then epidemiological observations of autoimmune disease in evaluated whether patients or controls had previously given women and with observations in transplantation biology birth to a male child. The nested PCR technique is used to led me to propose the hypothesis that non-host cells are detect very small amounts of DNA by conducting two involved in the pathogenesis of some autoimmune diseases. consecutive PCR reactions, the second of which is done on The hypothesis was proposed in the question “Is some the product from the first (using a second set of primers http://ard.bmj.com/ autoimmune disease auto-alloimmune or allo-auto- that are internal to the first set of primers). Eleven women immune?”1 The term “allo” refers to non-host cells from with SSc had positive results compared with none of 68 an individual of the same species. control women. Nine of the women with positive results In addition to a strong female predominance of autoim- had given birth to a male child, one had only daughters but mune disease the age specific incidence, for example of had a prior pregnancy termination, and for one the scleroderma (SSc) and primary biliary cirrhosis (PBC) in pregnancy history was unknown. Pregnancy history was women peaks in middle age—that is after childbearing unknown for the majority of controls but at least 30% had on September 24, 2021 by guest. Protected copyright. years.34 Interestingly, both of these diseases bear striking sons. Skin biopsy samples were examined using fluores- similarities to a known condition of human chimerism— cence in situ hybridisation and male cells reported in SSc chronic graft versus host disease (cGvHD) that can occur patients but not in controls (pregnancy history was not after haematopoietic stem cell (bone marrow) transplanta- provided for controls studied using in situ hybridisation). tion. Both SSc and cGvHD exhibit progressive induration Peripheral blood studies, although not quantitative, of the skin, often involve the gut and lungs and sometimes confirmed the observation that microchimerism is more have accompanying Sjögren’s syndrome and myositis.5–7 frequently found in women with SSc than controls. SSc-like manifestations of cGvHD often coexist with Persistent cells from a previous pregnancy do not explain cGvHD of the liver and cooccurrence of PBC and SSc has autoimmune disease in men or in women who have never 8 also been described. Patients with cGvHD disease usually Table 1 Persistent fetal microchimerism in SSc patients and controls have positive antinuclear antibody tests and antibodies to assessed by quantitative analysis of male DNA in women with prior birth topoisomerase I and antimitochondrial antibodies have of at least one son been described.910 Although similarities of cGvHD with Women with SSc Healthy women autoimmune diseases have been known, and an occasional (n=17) (n=16) case of SSc temporally related to pregnancy described, it Male cell equivalent, 11.1* 0.38 was the surprising recent finding that fetal microchimerism mean and range 0–61 0–2 persists for decades that launched the new model implicat- Age of woman, 46 45 ing microchimerism in the pathogenesis of some autoim- mean and range 33–64 25–61 Mean time since most 15.4 18.5 mune disease. recent son, mean, range 2 mo–28 y 2 mo–38 y As a first test of the hypothesis that persistent fetal Other pregnancies microchimerism is involved in some autoimmune diseases with daughters 10 9 we conducted a prospective study of women with SSc with with fetal loss 6 3 children born before disease onset and comparable control *p=0.0007 SSc v Control. Leader 519 been pregnant. However, there are alternative sources that dermatomyositis.21 Maternal microchimerism may be V could a ect these populations. These include engraftment implicated in some cases of systemic lupus based on an Ann Rheum Dis: first published as 10.1136/ard.58.9.518 on 1 September 1999. Downloaded from with cells from a twin, from a blood transfusion, or from experimental model of this disease that involves the induc- the mother. The first two of these have previously been tion of chimerism by introduction of parental cells into the described.13 14 Investigators pursing the goal of using cord progeny.22 23 Microchimerism could also play a part in dis- blood as a source for marrow transplantation have found eases that occur during pregnancy and pregnancy induced that non-shared maternal DNA can be detected in about modulation of disease activity in women who have a 40% of fetal cord blood samples.15 In addition, evidence for pre-existing autoimmune disease. In earlier studies we maternal cells has recently been described in elective found that remission of rheumatoid arthritis during terminations from 13 to 25 weeks gestation.16 17 Although pregnancy was associated with fetal-maternal HLA dispar- microchimerism was not investigated others have de- ity for HLA class II antigens, particularly for scribed longlasting tolerance to non-inherited maternal HLA-DQA1.24 In a study by Aractingi et al microchimer- HLA antigens.18 To pursue the possibility that maternal ism was investigated in women suVering from puritic erup- cells might sometimes persist long term we investigated a tion of pregnancy, a skin disorder that usually occurs dur- 47 year old SSc patient. HLA maternal specific PCR tests ing pregnancy. In an elegant and carefully done study the were conducted on DNA extracted from blood samples authors demonstrated microchimerism in skin biopsy sam- from the patient. Maternal specific DNA was detected in ples from patients but not from matched control women.25 samples from the patient from three separate draw dates. Mechanism(s) by which microchimerism might contrib- Sequencing confirmed the product to be identical to the ute to the pathogenesis of autoimmune diseases such as maternal HLA allele.19 Thus maternal cells may be added SSc have not been investigated. Studies have investigated to other potential sources of persistent microchimerism. chimerism in organ transplant recipients and patients with HLA molecules allow an individual to distinguish “self” cGvHD. Starzl and colleagues proposed the interesting from “other”, are critical determinants of immune re- hypothesis that donor cell microchimerism facilitates graft sponses, and specific HLA class II molecules have been acceptance as an explanation for chimerism in recipients of described in association with a variety of autoimmune dis- organ transplants who can withdraw immunosuppressive eases. In a corollary hypothesis1 it was proposed that prior medications without rejection.26 This hypothesis is appeal- birth of an HLA compatible child might increase risk of ing as an explanation for microchimerism during preg- subsequent autoimmune disease in the mother. For exam- nancy as pregnancy can be viewed as tolerance of a fetal ple, if a child’s cell persisted that was HLA similar but not allograft. However, an explanation for why fetal microchi- identical, could “autoimmune” disease result if later in life merism should persist for many years after pregnancy or a trigger such as a virus or environmental agent activated cause disease is not evident.

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