Immunohistochemical study of the inflammatory infiltrate in villitis of unknown etiology. A qualitative and quantitative analysis

Immunopathological insights into villitis of unknown etiology on the basis of transplant immunology

Villitis of unknown etiology (VUE) is an inflammatory disease characterized by the infiltration of maternal CD8 +T cells into the placental villi. Although the pathogenesis of VUE is still debated, dysregulation of the immune system appears to be an important factor in the development of the disease. Interaction of maternal T cells with the fetal antigens seems to be the trigger for the VUE onset. In this context, graft vs host disease (GVHD) and allographic rejection seem to share similarities in the VUE immunopathological mechanism, especially those related to immunoregulation. In this review, we compared the immunological characteristics of VUE with allograft rejection, and GVHD favoring a better knowledge of VUE pathogenesis that may contribute to VUE therapeutics strategies in the future.

M1 macrophages involved in the pathogenesis of placental chronic villitis of unknown etiology

INTRODUCTION

Placental villitis is characterized by the presence of inflammatory infiltrate in the placental villous. The objective of this study was to characterize in villitis of unknown etiology (VUE) of the human placentas the subpopulation of M1, important effector cells, and M2 macrophages, immunoregulatory cells.

METHODS

Sixteen cases of VUE and three control placentas were examined using immunohistochemistry with antibodies for CD3, CD68, CD11c, and CD163.

RESULTS

CD11c appeared predominantly in the inflamed villi when compared to the normal areas (p<.001). These cells corresponded to 41.2% of the macrophage population in the inflamed area and were mainly present inside the villi (36%). With regards to CD163, these cells tended to be in higher amounts in the inflamed villi when compared to CD11c and normal areas.

DISCUSSION

We conclude that the almost exclusive presence of M1 macrophages in the inflamed areas suggests the influence of these cells in the pathogenesis VUE. The greater amount of M2 in villitis and normal areas suggests a possible immunoregulatory mechanism of the inflammatory process in VUE.

Placental pathologic lesions with a significant recurrence risk - what not to miss!

Here, we review three important placental pathologies with significant clinical implications and recurrence risks. They are, in order of most to least frequently seen, villitis of unknown etiology, chronic histiocytic intervillositis, and massive perivillous fibrin deposition (also known as maternal floor infarction). These entities occur in both preterm and term gestations and are observed more frequently with maternal and obstetric disorders including prior pregnancy loss, hypertension/preeclampsia, and autoimmune disease. They are associated with, and probably the cause of, significant perinatal morbidity and mortality including intrauterine growth restriction, fetal and neonatal demise, and fetal/neonatal neurocompromise (seizures and cerebral palsy). All three entities have high recurrence risks, with recurrence rates ranging from 34 to 100%. The histologic features of villitis of unknown etiology, chronic histiocytic intervillositis, and massive perivillous fibrin deposition are described herein. We discuss the clinical associations and suggest the subsequent clinical and pathological evaluation. Hypotheses as to the biology of these lesions are reviewed.

Chronic villitis of unknown etiology and massive chronic intervillositis have similar immune cell composition

INTRODUCTION

Chronic villitis of unknown etiology (CVUE) and massive chronic intervillositis (MCI) are placental lesions associated with infiltration of mononuclear cells in the chorionic villi and the intervillous spaces, respectively. It is not well known whether immune cells in CVUE and MCI have similar phenotypic characteristics.

METHODS

A cross-sectional study of third trimester placentas was conducted to identify immune cell subpopulations in CVUE and MCI (n = 17/group). CVUE was diagnosed with H&E staining and antibody to CD3 in serial sections; and MCI, by the presence of massive infiltration of mononuclear cells in the intervillous spaces. Immune cells, ICAM-1 expression and nuclear factor κB (NF-κB) activation were determined immunohistochemically.

RESULTS

CVUE and MCI showed similar infiltrates, mainly CD68+ and CD3+ cells. Most cells (>80%) were CD45RB+, and one third were CD45RO+ in both lesions. There were slightly more CD8+ than CD4+ cells in both CVUE and MCI. More than 90% of cells in CVUE and MCI were ICAM-1+ with NFκB nuclear localization. Syncytiotrophoblast ICAM-1 expression was significantly (p < 0.001) higher in MCI (mean of 81.0; range of 71.6-86.0) than in CVUE (52.4; 36.4-59.4) or normal placentas (0.2; 0.0-0.6). Both, failure of physiologic transformation of spiral arteries and placental atherosclerosis-like lesions of atherosis were significantly more frequent in MCI than in CVUE or normal placentas (p = 0.044 and p = 0.007, respectively).

DISCUSSION

These finding suggest that MCI and CVUE have very similar infiltration of immune cells although MCI has more severe placental lesions.

Viral infection in placenta relevant cells--a morphological and immunohistochemical cell culture study

Viral infections in pregnancy are known to cause fetal malformation, growth restriction, and even fetal death. Macroscopic placental examination usually shows slight and unspecific changes. Histology may show secondary, non-specific tissue reaction, i.e. villitis with lymphocytic invasion. Primary specific morphology characteristics are known for some virus, like cytomegalovirus, parvovirus, and herpes simplex, however many viral infections show non-specific changes. Placenta relevant cells as human first trimester trophoblasts HTR8/SVneo, primary human umbilical vein endothelial cells (HUVEC), and primary human embryonic fibroblasts were examined following infection with commonly occurring virus like adenovirus and enterovirus. Morphology in routine stained sections and virus-specific immunostains were studied 4, 8, 24, 48, 72 h after infection. Nuclear enlargement was seen in the infected cells. A specific diagnosis of adenovirus or enterovirus infection, however, was not possible without specific immunostains.

Follow-up study of lympho-histiocytic villitis and incidental retroplacental hematoma

Placentas are usually submitted for pathologic examination based on obstetrical indications. We hypothesized that the placenta may have diagnostic value to the infant independent of obstetrical events. We specifically tested whether lymphohistiocytic villitis (noninfectious) would predict autoimmune or alloimmune disease based on transfer of activated maternal T-cells to the fetus and whether clinically silent placental separations (retroplacental hematomas, RPH) would predict neurologic injury in the infant. All placentas from consecutive deliveries had a routine pathologic examination of the placenta. The infants with placentas demonstrating inflammation of >1% of villi or RPH >2 cm and matched controls had their hospital charts reviewed and parental interviews by telephone at 5 to 7 years of age. The children of consented patients were also searched for in the office visits of the University of Louisville Pediatric Neurology and Rheumatology divisions. One thousand six hundred eighty-four patients consented to the follow-up study. We found no cases of autoimmune disease among 17 children with villitis >1%. Of 16 infants with RPH, 1 had cerebral palsy but with other placental findings, 1 had lethal hydranenecephaly, and the remainder had no adverse outcome. Of 15 children seen by a pediatric neurologist, none had the same placental lesion. The specific lesions of lymphohistiocytic villitis or asymptomatic RPH do not predict significant pediatric disease by 7 years of age. At least for these 2 lesions, the placenta does not have diagnostic value to the infant.

Specific infiltration pattern of FOXP3+ regulatory T cells in chronic histiocytic intervillositis of unknown etiology

INTRODUCTION

Chronic histiocytic intervillositis of unknown etiology (CIUE) is a rare placental lesion characterized by an intervillous mononuclear inflammatory infiltrate of maternal origin. Although the mechanism and origin of these lesions are currently not understood, they appear to be related to an immune conflict between mother and fetus cells.

AIM

To clarify the inflammatory cell profile and evaluate the T regulatory lymphocyte (Treg) status in CIUE.

MATERIALS AND METHODS

All cases of CIUE that occurred over an 8-year period were analyzed using immunohistochemistry.

RESULTS

The inflammatory profile of CIUE was characterized by a clearly predominant component of histiocytic cells (80% ± 6.9) associated with some T cells (24% ± 5.7). The ratio of CD4+ versus CD8+ T cells was close to 1. This profile differs from infectious disease and chronic histiocytic villitis, the main differential diagnoses of CIUE. As for normal pregnancies most regulatory T cells were localized in the decidua basalis. Nevertheless, their appearance was also noted in the intervillous space. In both the intervillous space and the deciduas the number of Tregs gradually increased from grade 1 to 3.

CONCLUSION

We found that CIUE is associated with an increase in Treg lymphocytes in the decidua basalis and the intervillous space. Contrary to previously published data on human miscarriage, this result appears to be specific to CIUE and would support the hypothesis of an immunopathological disorder for CIUE.

Involvement of Hofbauer cells and maternal T cells in villitis of unknown aetiology

AIMS

The nature of villitis of unknown aetiology (VUE) is intriguing in terms of its aetiology, origin of inflammatory cells and immunophenotype of T cells involved. The aim was to determine the origin of macrophages and the immunophenotype of T lymphocytes in VUE associated with various complications of pregnancy.

METHODS AND RESULTS

Placentas with VUE (n = 45) were studied by chromogenic in-situ hybridization (CISH) for Y chromosome (DYZ1) and immunohistochemistry for CD14, CD68, Ki67 (n = 10; all from male neonates) and a panel of T-cell antigens (CD3, CD4 and CD8) (n = 35). All of the placentas from male neonates showed CISH+ signals from Y chromosomes in the majority of macrophages, but not in lymphocytes, indicating that the macrophages were of fetal origin. Many macrophages of the affected chorionic villi were Ki67+, suggesting that they are hyperplastic Hofbauer cells. Among the lymphocytes, CD8+ T cells outnumbered CD4+ T cells in all placentas with different obstetrical conditions.

CONCLUSIONS

We define primary components of VUE as maternal CD8+ T cells and hyperplastic Hofbauer cells. We propose that VUE is a unique inflammatory reaction where the leucocytes from two hosts are key partners, analogous to either allograft rejection or graft-versus-host disease.

Villitis of unknown etiology: noninfectious chronic villitis in the placenta

Villitis of unknown etiology (VUE) is an important pattern of placental injury occurring predominantly in term placentas. Although overlapping with infectious villitis, its clinical and histologic characteristics are distinct. It is a common lesion, affecting 5% to 15% of all placentas. When low-grade lesions affecting less than 10 villi per focus are excluded, VUE is an important cause of intrauterine growth restriction and recurrent reproductive loss. Involvement of large fetal vessels in the placenta (obliterative fetal vasculopathy) in cases of VUE is a strong risk factor for neonatal encephalopathy and cerebral palsy. Although the etiology of the eliciting antigen is unknown, many other characteristics of the immune response have been clarified. VUE is caused by maternal T lymphocytes, predominantly CD8-positive, that inappropriately gain access to the villous stroma. Fetal antigen-presenting cells (Hofbauer cells) expand and are induced to express class II major histocompatibility complex molecules. Maternal monocyte-macrophages in the perivillous space likely amplify the immune response. Although much speculation exists that VUE represents a host-versus-graft reaction analogous to transplant rejection, other eliciting antigens have not been excluded. Irrespective of target antigen or antigens, the pathophysiologic implications of having activated maternal lymphocytes within vascularized fetal tissues are not trivial.

ICAM-1 is Overexpressed by Villous Trophoblasts in Placentitis

Although an in vitro study has hypothesized that expression of ICAM-1 by villous trophoblasts could be important for the influx of maternal immune cells in villitis, it remains to be shown whether the same phenomenon occurs in human villitis. To investigate the expression of ICAM-1 by villous trophoblasts, its relationship with rupture of the trophoblastic barrier and influx of immune cells into the villi, we analysed 18 paraffin-embedded placentas with placentitis (5 by Toxoplasma gondii, 3 by Trypanosoma cruzi, 2 by Paracoccidioides brasiliensis and 8 of unknown aetiology - VUE) and 8 control placentas for detection of ICAM-1 by immunohistochemistry. All cases but one of placentitis showed trophoblast overexpression of ICAM-1 in the inflamed villi, located almost exclusively next to the areas of trophoblastic rupture. The villitis cases (caused by T. cruzi, T. gondii and VUE) presented leukocyte adherence in the areas of trophoblastic rupture. When the inflammatory reaction was situated in the intervillous space (placentitis by P. brasiliensis), in spite of the trophoblastic rupture and ICAM-1 overexpression there was no leukocyte influx into villi. None of the control placentas showed ICAM-1 expression by the trophoblast. We concluded that overexpression of ICAM-1 by villous trophoblasts occurs during placentitis characterized by accumulation of leukocytes in the villous or intervillous space and probably plays an important role in the rupture of the trophoblastic barrier. The influx of immune cells into the villi appears to be mediated by ICAM-1 but the location of the antigen within villous stroma is certainly a crucial factor for its occurrence.

Chronic villitis in untreated neonatal alloimmune thrombocytopenia: an etiology for severe early intrauterine growth restriction and the effect of intravenous immunoglobulin therapy

OBJECTIVE

The objective of the study was to examine placental histopathology in intravenous immunoglobulin-treated and untreated neonatal alloimmune thrombocytopenia and correlate pathological findings with clinical outcomes.

STUDY DESIGN

Placentas from 14 neonatal alloimmune thrombocytopenia-affected pregnancies were identified. Maternal antepartum treatment with intravenous immunoglobulin and pregnancy outcomes were abstracted from medical records. Placental histopathology and clinical outcomes were compared between intravenous immunoglobulin and no intravenous immunoglobulin treatment groups using Fisher's exact test. One subject, treated only after an intracranial hemorrhage (ICH) was diagnosed, was excluded from the analysis. P < .05 was considered significant.

RESULTS

Untreated pregnancies demonstrated a lymphoplasmacytic chronic villitis not seen in the intravenous immunoglobulin-treated pregnancies (P = .005). Intrauterine growth restriction and intrauterine fetal demise occurred as frequently as ICH in the untreated group. No ICH, intrauterine growth restriction, or intrauterine fetal demises occurred in the treated group, although the P value was not significant.

CONCLUSION

Chronic villitis is frequently manifest in neonatal alloimmune thrombocytopenia, with intravenous immunoglobulin alleviating this inflammatory immunologic response. We suspect a more universal role for the maternal antibody, such as fetal endothelial cell damage, in the sequelae of neonatal alloimmune thrombocytopenia.

Placental inflammation

Placental inflammatory disorders represent a diverse and important category of pathological processes leading to fetal and neonatal morbidity and mortality. These processes can be divided into two broad subcategories, those caused by micro-organisms and those caused by host immune responses to non-replicating antigens. The mechanisms by which these inflammatory processes cause death and disability are diverse and can be separated into four distinct classes: placental damage with loss of function, induction of premature labour and subsequent preterm birth, release of inflammatory mediators leading to fetal organ damage and transplacental infection of the fetus. Each specific inflammatory process can be modulated by properties of the specific organism, the route and timing of infection and variations in the host's genetic background and immune responsiveness. All of these factors combine to produce specific patterns of placental pathology that can be used to guide treatment, predict complications and explain adverse outcome.

Characterization of inflammation in syphilitic villitis and in villitis of unknown etiology

Chronic villitis is a histologic diagnosis that may be either associated with infection, or termed villitis of undetermined etiology (VUE). The lymphocytic infiltrate in VUE has been reported to consist of maternal lymphocytes, but the origin of the lymphocytic infiltrate in infectious villitis has not been identified. The purpose of our study was to compare the maternal vs. fetal origin of the infiltrating lymphocytes in VUE and syphilitic villitis, and to expand the immunophenotypic data provided by previous studies. Paraffin-embedded placentas from four males with VUE and two males with syphilitic villitis were subjected to fluorescence in situ hybridization (FISH) for the X and Y chromosomes. Serial sections were stained with antibodies to CD3, CD4, CD8, CD68, HLA-DR, and CD20. Quantitation of the relative number of cells marking with each antibody was done for four villi in each slide. CD3 lymphocytes predominated in both VUE and syphilitic villitis, with slightly more CD8 cells compared to CD4 cells. CD68 and HLA-DR positive cells were as frequent as CD3 cells, and B-lymphocytes were rare. Maternal cells were the predominant intravillous population in both VUE and syphilitic villitis, and neutrophils in syphilitic villitis were also maternal. These data indicate that the immune response in both syphilitic villitis and VUE is similar, raising the possibility of a similar immunopathogenetic pathway.

Human cytomegalovirus-induced upregulation of intercellular cell adhesion molecule-1 on villous syncytiotrophoblasts

Human cytomegalovirus (HCMV) is secreted apically from villous trophoblasts, thus congenital infection is not likely to occur by basal release across the basement membrane. As an alternative route, we hypothesize that an HCMV-infected villous syncytiotrophoblast (ST) upregulates intercellular adhesion molecule (ICAM)-1, causing blood monocytes to bind to the ST and induce apoptosis. Purified (>99.99%) populations of human villous trophoblasts were differentiated into an ST-like culture, infected with HCMV strain AD169, and assessed for ICAM-1 expression by immunofluorescence. Infection strongly upregulated ICAM-1 24 h after challenge. ICAM-1 was also stimulated by transfection with viral genes IE2-55, IE1-72, and IE2-86, but not by UV-inactivated virus. Infection with a green fluorescent protein recombinant virus allowed infection and ICAM-1 expression to be topographically located. We found that ICAM-1 was expressed on both infected and noninfected cells. Furthermore, antibody to tumor necrosis factor (TNF)alpha and, to a lesser extent, interleukin (IL)1 beta inhibited ICAM-1 upregulation on noninfected cells but not on infected cells. We conclude that HCMV IE proteins stimulate ICAM-1 expression on villous trophoblasts by paracrine release of TNF alpha and IL1 beta, as well as by a direct effect on infected cells.

Investigation of stillbirth

The pathologic investigation of stillbirth is often frustrating, and may be viewed as unrewarding, because the reason for death of the infant frequently is not identifiable. This outline attempts to identify an approach to the examination of the stillborn and accompanying placenta, with appropriate use of ancillary studies that may uncover the cause of death and/or identify factors that could prejudice future pregnancies.

Immunopathology of the implantation site utilizing monoclonal antibodies to natural killer cells in women with recurrent pregnancy losses

PROBLEM

Placental lesions of 71 women with documented recurrent spontaneous abortions of unknown etiology were evaluated using immunohistochemical staining.

METHOD OF STUDY

Placental tissue blocks (less than 12 weeks gestation) from prior pregnancy losses were obtained, recut, and analyzed utilizing monoclonal antibody to identify the trophoblast (cytokeratin 8/18) and natural killer (NK) cells (CD57) at the implantation site. The following features were evaluated: trophoblast invasion pattern; syncytium formation; vasculitis and thromboembolism of decidual vessels; decidual inflammation; decidual necrosis; fibrin deposition at the decidual necrosis site; mononuclear-cell infiltration in villi and intervillous space; perivillous fibrin deposition; trophoblast morphology; and quantitation of CD57+ NK cells within the decidual tissue near the implantation site. Controls consisted of 20 healthy women with no history of recurrent pregnancy losses, who had their pregnancies electively terminated.

RESULTS

Of the women studied, 29.6% demonstrated elevated CD57+ NK cells at the implantation site (P = 0.030), 54.1% had inadequate cytotrophoblast invasion depth (P = 0.000), 44.1% demonstrated inadequate syncytium formation (P = 0.004), and 33.9% presented thromboembolism in decidual vessels (P = 0.025).

CONCLUSION

Some women with recurrent spontaneous abortions demonstrate abnormal placental lesions at the implantation site. Immunopathologic evaluation of the placental implantation site that terminated in a spontaneous abortion may reveal the immunopathogenesis of previous pregnancy losses.

Chronic chorioamnionitis: a clinicopathologic and immunohistochemical study

Lymphocytic inflammation of the fetal membranes is unusual and has been termed chronic chorioamnionitis. We report the clinicopathologic and immunohistochemical findings in 31 placentas with chronic chorioamnionitis. The most common histopathologic association was chronic villitis of unknown etiology, which was identified in 22 (71%) of the 31 placentas. The severity of the chronic villitis did not correlate with the severity of chronic chorioamnionitis. Additional placental findings included chronic intervillositis in two, fetal vessel thrombosis in five, hemorrhagic endovasculitis in four, decidual chronic vasculitis in three, and atherosis in one. Maternal history included pregnancy-induced hypertension in six and diabetes in one. Twelve infants were preterm, and five had intrauterine growth retardation. There was no neonatal sepsis or death. Immunohistochemical staining in areas of chronic chorioamnionitis showed CD3+ and CD8+ cells present in moderate numbers, and CD4+ cells in smaller numbers. CD20+ and CD56+ cells were rare or absent. Chronic chorioamnionitis is commonly associated with chronic villitis of unknown etiology, shares similar clinical associations, and may have a related cause, possibly immunologic.

Immunohistochemical studies of human uteroplacental tissues from first-trimester spontaneous abortion

OBJECTIVE

Atypical expression of human leukocyte antigen histocompatibility molecules or complement regulatory proteins by placental trophoblast has been hypothesized as a mechanism for spontaneous abortion. The purpose of this study was to determine expression of these proteins by placental villous trophoblast and to identify leukocyte populations within uteroplacental tissues from women with their first spontaneous abortion, their fourth or more recurrent spontaneous abortion, and from women having elective pregnancy termination.

STUDY DESIGN

Fresh uteroplacental tissues were obtained at 6 to 9 weeks' gestation from eight women with their first spontaneous abortion, 20 women experiencing their fourth or more unexplained recurrent spontaneous abortion, and 20 women having an elective pregnancy termination. These tissues were analyzed immunohistochemically for human leukocyte antigen histocompatibility molecules (class I and II major histocompatibility complexes), complement regulatory proteins (CD46, CD55), and leukocyte phenotypes (CD45, CD3, CD14, CD56).

RESULTS

There was absence of cell surface expression of class I and II human leukocyte antigen molecules but strong trophoblast expression of complement regulatory proteins in all villous placental samples. Leukocyte infiltration was noted in all decidual specimens. The predominant decidual leukocyte population was CD3-negative, CD56-positive cells, except in four cases of recurrent abortion where the normal ratio (< or = 2:3) of CD14-positive macrophages to CD56-positive leukocytes was > 2:1. There was an unusual retention of maternal class II major histocompatibility complex-positive leukocytes within intervillous spaces attached to the apical surface of syncytiotrophoblast from one individual with recurrent abortion.

CONCLUSION

Our data do not support the hypothesis that some cases of recurrent spontaneous abortion result from atypical expression of human leukocyte antigen histocompatibility molecules or lack of complement regulatory protein expression by placental villous trophoblast. These data suggest that occasional cases of recurrent spontaneous abortion could be associated with an impaired CD56-positive leukocyte response in the early decidualized endometrium.

Maternal cells in chorionic villi from placentae of normal and abnormal human pregnancies

PROBLEM

We asked if activated macrophages and CD4 positive T lymphocytes in placental chorionic villi with villitis were of maternal or fetal origin.

METHOD

We employed a double antibody immunocytochemical technique on placental sections from three normal and four abnormal pregnancies with small-for-gestational-age infants. All studied placentae were mismatched for the maternal-fetal HLA-DRw 52 antigen. Areas of immunopathology were identified by using a monoclonal antibody to a monomorphic determination on HLA-DR, and the origin of immunological cells in areas of immunopathology was identified by using a monoclonal antibody to a polymorphic determinant on HLA-DRw 52.

RESULTS

We used a double antibody technique that employed monoclonal antibodies to HLA-DR and HLA-DRw 52 antigens and placentae that were mismatched for the maternal-fetal HLA-DRw 52 antigen. We found that the vast majority of immunological cells within villi with inflammation were of maternal origin. Quantitative studies showed that between 75 and 100% of the cells in normal as well as in abnormal pregnancies were of maternal origin, and that abnormal pregnancies had a significantly higher percentage of villi with maternal cellular infiltrates.

CONCLUSION

Our data show unequivocally that cells in areas of placental immunopathology are predominantly of maternal origin, and that abnormal pregnancies are associated with significantly more villi containing immunological cells of maternal origin.