β2-glycoprotein I and protection from anti-SSA/Ro60-associated cardiac manifestations of neonatal lupus

Maternal and infant outcomes of pregnancy associated with anti-SSA/RO antibodies: a systematic review and meta-analysis

OBJECTIVE

The relationship between anti-SSA/RO antibodies and pregnancy has been reported previously, and we aim to visualize the rates of maternal and infant outcomes with anti-SSA/RO.

METHODS

We systematically searched records from Pubmed, Cochrane, Embase, and Web of Science databases, pooled incidence rates of adverse outcomes of pregnancy, and 95% confidence intervals (CIs) were performed with RStudio.

RESULTS

A total of 890 records comprising 1675 patients and 1920 pregnancies were searched from the electronic databases. For maternal outcomes, the pooled estimate rates were 4% for termination of pregnancy, 5% for spontaneous abortion, 26% for preterm labor, and 50% for cesarean operation. While for fetal outcomes, the pooled estimate rates were 4% for perinatal death, 3% for intrauterine growth retardation, 6% for endocardial fibroelastosis, 6% for dilated cardiomyopathy, 7% for congenital heart block, 12% for congenital heart block recurrence, 19% for cutaneous neonatal lupus erythematosus, 12% for hepatobiliary disease and 16% for hematological manifestations. A subgroup analysis of congenital heart block prevalence was performed, diagnostic method and study region were found to affect heterogeneity to some extent.

CONCLUSION

Cumulative analysis of data from real-world studies confirmed adverse pregnancy outcomes of women with anti-SSA/RO, serves as a reference and a guide for the diagnosis and subsequent treatment of these women, thereby enhancing maternal and infant health. Additional studies with real-world cohorts are required to validate these results.

Autoimmune-mediated congenital heart block

Autoimmune-mediated congenital heart block (CHB) is a severe manifestation of neonatal lupus in which conduction tissues of the fetal heart are damaged. This occurs due to passive transference of maternal anti-SSA/Ro and anti-SSB/La autoantibodies and subsequent inflammation and fibrosis of the atrioventricular (AV) node. Notably, the disease manifests after the fetal heart has structurally developed, ruling out other anatomical abnormalities that could otherwise contribute to the block of conduction. Complete AV block is irreversible and the most common manifestation of CHB, although other cardiac complications such as endocardial fibroelastosis (EFE), dilated cardiomyopathy, and valvular insufficiency have been observed. In this review, we detail the classification, prevalence, pathogenesis, and clinical management recommendations for autoimmune CHB.

Evolutionary conservation of the lipopolysaccharide binding site of β2-glycoprotein I

β2-Glycoprotein I (β2GPI) is a highly abundant plasma protein and the major antigen for autoantibodies in the antiphospholipid syndrome. Recently, we have described a novel function of β2GPI as scavenger of lipopolysaccharide (LPS). With this in mind we investigated the conservation of β2GPI in vertebrates and set out to identify the binding site of LPS within β2GPI. The genome sequences of 42 species were surveyed. Surface plasmon resonance (SPR) was performed with peptides to characterise the binding site of β2GPI for LPS. β2GPI could be identified in most tested vertebrates with a high overall amino acid homology of 80% or more in mammals. SPR revealed that a synthesised peptide (LAFWKTDA) from domain V of β2GPI was able to compete for binding of β2GPI to LPS. The AFWKTDA sequence was completely conserved in all mammals. The peptide containing the LPS binding site attenuated the inhibition by β2GPI in a cellular model of LPS-induced tissue factor expression. Other important sites, such as the binding site for anionic phospholipids and the antiphospholipid antibody binding epitope, were also preserved. β2GPI is highly conserved across the animal kingdom, which suggests that the function of β2GPI may be more important than anticipated.

Anti-Ro and Concomitant Anti-La Autoantibodies Strongly Associated With Anti-oxLDL or Anti-Phospholipid Antibody in Systemic Lupus Erythematosus

BACKGROUND

Premature atherosclerosis is observed in systemic lupus erythematosus (SLE). Oxidative modification of LDL is associated with atherosclerotic plaque formation.

OBJECTIVES

We hypothesized that anti-oxidized LDL (oxLDL) and anti-phospholipid (APL) in SLE sera would segregate with specific antibody subsets, and that anti-oxLDL antibodies will linger in circulation over an extended period.

PATIENTS AND METHODS

Sixty-seven SLE and control subjects and two SLE subjects with sera collected longitudinally for 13 years were tested for anti-oxLDL and IgG/IgM/IgA APL antibodies.

RESULTS

Anti-oxLDL ELISA values above 57.48 Activity Units (AcU) (means of normals + 3 standard deviations) and anti-IgG/IgM/IgA APL above 10 phospholipid units (PU) were considered positive. Average anti-oxLDL was 67.7 ± 50.5 AcU in SLE compared to 23.9 ± 11.19 AcU in normals (P = 0.018). Ten out of ten subjects with anti-Ro60/anti-La/anti-Ro52 antibodies had highly significant (P < 0.0001) anti-oxLDL (127.29 ± 45.67 AcU) and IgG APL (18.66 ± 7.4 PU) (P < 0.02). Subjects with anti-RNP were positive for anti-oxLDL (P < 0.002), but subjects with anti-Ro60/anti-Ro52 and subjects negative for extractable nuclear antigen (ENA) antibody were not positive for anti-oxLDL. Anti-oxLDL/anti-IgG APL remained significantly elevated in two patients studied longitudinally. Interestingly, one developed anti-oxLDL/anti-APL antibodies several years before anti-Ro60 development.

CONCLUSIONS

Presence of antibodies against Ro RNP and La, and RNP is highly associated with developing anti-oxLDL and APL antibodies in SLE. It will be clinically important to see if cardiovascular events occur in these SLE subsets having elevated anti-oxLDL and APL antibodies. Emergence of anti-oxLDL/IgG APL before anti-Ro60 over time in a patient indicates that these antibodies could not be cross-reactive in nature, at least in this particular patient.

Autoimmune congenital heart block: complex and unusual situations

Autoimmune congenital heart block (ACHB) is an immune-mediated cardiac disease included among the manifestations collectively referred to as neonatal lupus. The placental transference of maternal Ro/La autoantibodies may damage the conduction tissues during fetal development leading to blocking of signal conduction at the atrioventricular (AV) node in an otherwise structurally normal heart. Irreversible complete AV block is the main cardiac manifestation of ACHB, but some babies may develop endocardial fibroelastosis, valvular insufficiency, and/or frank cardiomyopathies with significantly reduced cardiac function requiring transplant. The severity of ACHB is illustrated by a global mortality rate of 20% and pacemaker rates of at least 64%, often within the first year of life. This review analyses the main complex and/or unusual clinical situations associated with ACHB, including unusual maternal immunological profiles, infrequent maternal autoimmune diseases, cardiac damage unrelated to AV block, fetal invasive management, late complications after birth, risk of congenital heart block (CHB) in ovodonation and in vitro fertilization techniques, the role of maternal features other than autoimmunity, the influence of the birth order or the risk of CHB in twins and triplets.

Endosomal Toll-like receptors in clinically overt and silent autoimmunity

Toll-like receptors (TLRs), first identified as pattern recognition receptors, are now recognized to serve as a key interface between innate and adaptive immunity. Systemic lupus erythematosus (SLE) is characterized by both continuous and cyclic stimulation of the innate and adaptive immune system by endogenous nucleic acids released from apoptotic or necrotic cells. TLR7 and TLR9 function as innate sensors of viral infection as their ligands are ssRNA and dsDNA, respectively. Recognition of self nucleic acids by endosomal TLRs in B cells and pDCs is thought to be an important step in the pathogenesis of SLE, generating anti-nuclear antibodies and producing type I IFN. In this review, we take a specific look at how TLR7, non-coding RNA, and SSA/Ro60 can contribute to clinical autoimmunity and organ damage in the context of neonatal lupus (NL). Although 15 times less common than SLE, NL provides a unique opportunity to study two different aspects of autoimmunity: passively acquired tissue injury in a developing fetus and clinical progression of disease in an asymptomatic mother found to have anti-Ro60 autoantibodies only after identification of heart block/rash in a child. Finally, we discuss hydroxychloroquine (HCQ) use by asymptomatic subjects which may forestall the clinical expression of autoimmunity.

Warm antibody hemolytic anemia—a rare presentation of neonatal lupus

Neonatal lupus erythematosus (NLE) affects 1%–2% pregnant females with autoimmunity. An infant presented with steroid refractory hemolytic anemia as a manifestation of NLE. A trial of withholding breastfeeding had a transient response, but infant was eventually put on cyclosporin therapy to control the hemolysis. Now he is thriving well and transfusion free.

Autoantibodies in Sjögren's Syndrome

We compiled information on antibodies in Sjögren syndrome, focusing more on clinical manifestations associated with anti-Ro/SSA and anti-La/SSB antibodies and studies regarding novel antibodies. We reviewed previous as well as most recent studies with the subject heading Sjogren in combination with antibodies and congenital heart block (CHB). Almost half of asymptomatic mothers giving birth to children with CHB ultimately develop Sjögren. We discussed studies concerning the presence of antibodies predating clinical manifestations of disease. Studies in the future are required to ascertain the pathogenic mechanisms associated with these antibodies and the specific clinical manifestation related to new autoantibodies.

Relationship between phosphatidylserine exposure and serum-dependent opsonization in phagocytes

AIM: To investigate the relationship between the exposure of phosphatidylserine (PS) and serum-dependent opsonization in peripheral blood mononuclear cells (PBMCs), to lay a foundation for exploring the influence of physiological microenvironment on the function of phagocytes.

METHODS: PBMCs were isolated from the peripheral blood of healthy individuals using Ficoll-paque and treated by RPMI 1640 medium with or without serum after washing with PBS. The phosphatidylserine (PS) exposure was detected by annexin V staining before and after in vitro serum incubation. Malondialdehyde (MDA) in treated PBMCs was examined by spectrophotometry to evaluate the interference of lipid peroxidation. The PS exposure in different subsets of PBMCs was analyzed by flow cytometry with anti-CD3, anti-CD56 and anti-HLA-DR staining. Phagocytosis was detected by FCM after incubation with bacteria expressing green fluorescent protein (GFP).

RESULTS: PS⁺ cells significantly increased in PBMCs after serum incubation, and short-term serum incubation immediately induced the increase of PS⁺ cells. Serum incubation had no influence on the membrane MDA content, which excluded the interference by the products of lipid peroxidation. Cell subset analysis showed that HLA-DR⁺ mononuclear phagocytes were the main cells exposing PS in PBMCs and significantly increased in Annexin V⁺ cells. Bacterial phagocytosis showed that the exposed PS was involved in the serum-dependent opsonization.

CONCLUSION: The exposure of PS is serum-dependent and is involved in the opsonization of bacteria by PBMCs.

Molecular mechanisms of congenital heart block

Autoantibody-associated congenital heart block (CHB) is a passively acquired autoimmune condition associated with maternal anti-Ro/SSA antibodies and primarily affecting electric signal conduction at the atrioventricular node in the fetal heart. CHB occurs in 1-2% of anti-Ro/SSA antibody-positive pregancies and has a recurrence rate of 12-20% in a subsequent pregnancy. Despite the long-recognized association between maternal anti-Ro/SSA autoantibodies and CHB, the molecular mechanisms underlying CHB pathogenesis are not fully understood, but several targets for the maternal autoantibodies in the fetal heart have been suggested. Recent studies also indicate that fetal susceptibility genes determine whether an autoantibody-exposed fetus will develop CHB or not, and begin to identify such genes. In this article, we review the different lines of investigation undertaken to elucidate the molecular pathways involved in CHB development and reflect on the hypotheses put forward to explain CHB pathogenesis as well as on the questions left unanswered and that should guide future studies.

The heart and pediatric rheumatology

Recent advances in Kawasaki disease have included attempts to define genes involved in its pathogenesis. There have been recent advances in the studies of rheumatic carditis, leading to a better understanding of the mechanism of the disease. Histologic evaluation of patients with neonatal lupus erythematosus has revealed fibrosis with collagen deposition and calcification of the atrioventricular node. Therapy for cardiac involvement in systemic juvenile idiopathic arthritis should involve treatment of the underlying disease and systemic inflammatory state, and typically includes nonsteroidal antiinflammatory drugs, corticosteroids, disease-modifying drugs, and biologic therapies targeting tumor necrosis factor-alpha, interleukin-1, and interleukin-6.

Ro60 requires Y3 RNA for cell surface exposure and inflammation associated with cardiac manifestations of neonatal lupus

Cardiac neonatal lupus (NL) is presumed to arise from maternal autoantibody targeting an intracellular ribonucleoprotein, Ro60, which binds noncoding Y RNA and only becomes accessible to autoantibodies during apoptosis. Despite the importance of Ro60 trafficking in the development of cardiac NL, the mechanism underlying cell surface exposure is unknown. To evaluate the influence of Y RNA on the subcellular location of Ro60 during apoptosis and activation of macrophages, stable Ro60 knockout murine fibroblasts expressing wild-type or mutated FLAG-Ro60 were assessed. FLAG3-Ro60(K170A R174A) binds Y RNA, whereas FLAG3-Ro60(H187S) does not bind Y RNA; fibroblasts expressing these constructs showed equivalent intracellular expression of Ro60. In contrast, apoptotic fibroblasts containing FLAG3-Ro60(K170A R174A) were bound by anti-Ro60, whereas FLAG3-Ro60(H187S) was not surface expressed. RNA interference of mY3 RNA in wild-type fibroblasts inhibited surface translocation of Ro60 during apoptosis, whereas depletion of mY1 RNA did not affect Ro60 exposure. Furthermore, Ro60 was not exposed following overexpression of mY1 in the mY3-depleted fibroblasts. In an in vitro model of anti-Ro60-mediated injury, Y RNA was shown to be an obligate factor for TLR-dependent activation of macrophages challenged with anti-Ro60-opsonized apoptotic fibroblasts. Murine Y3 RNA is a necessary factor to support the surface translocation of Ro60, which is pivotal to the formation of immune complexes on apoptotic cells and a TLR-dependent proinflammatory cascade. Accordingly, the Y3 RNA moiety of the Ro60 ribonucleoprotein imparts a critical role in the pathogenicity of maternal anti-Ro60 autoantibodies.

A central role of plasmin in cardiac injury initiated by fetal exposure to maternal anti-Ro autoantibodies

OBJECTIVE

Cardiac neonatal lupus (cardiac-NL), initiated by surface binding of anti-Ro60 autoantibodies to apoptotic cardiocytes during development, activates the urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) system. Subsequent accumulation of apoptotic cells and plasmin generation facilitates increased binding of anti-Ro60 by disrupting and cleaving circulating β2-glycoprotein I (β2GPI) thereby eliminating its protective effect. The association of soluble levels of components of the uPA/uPAR system with cardiac-NL was examined.

METHODS

Levels of the uPA/uPAR system were assessed by ELISA in cord blood and immunohistological evaluation of autopsies.

RESULTS

uPA, uPAR and plasminogen levels were each significantly higher in cord blood from cardiac-NL (n = 35) compared with non-cardiac-NL (n = 26) anti-Ro-exposed neonates: 3.3 ± 0.1 vs 1.9 ± 0.05 ng/ml (P < 0.0001), 6.6 ± 0.3 vs 2.1 ± 0.2 ng/ml (P < 0.0001) and 435 ± 34 vs 220 ± 19 ng/ml (P < 0.0001), respectively. In three twin pairs discordant for cardiac-NL, the twin with cardiac-NL had higher levels of uPA, uPAR and plasminogen than the unaffected twin (3.1 ± 0.1 vs 1.9 ± 0.05 ng/ml; P = 0.0086, 6.2 ± 1.4 vs 2.2 ± 0.7 ng/ml; P = 0.147 and 412 ± 61 vs 260 ± 27 ng/ml; P = 0.152, respectively). Immunohistological evaluation of three hearts from fetuses dying with cardiac-NL revealed macrophages and giant cells expressing uPA and plasminogen in the septal region.

CONCLUSION

Increased soluble uPA, uPAR and plasminogen in cord blood and expression in affected tissue of fetuses with cardiac-NL supports the hypothesis that fetal cardiac injury is in part mediated by plasmin generation initiated by anti-Ro binding to the apoptotic cardiocyte.

Long-term Ro60 humoral autoimmunity in primary Sjögren's syndrome is maintained by rapid clonal turnover

Long-term humoral autoimmunity to RNA-protein autoantigens is considered a hallmark of systemic autoimmune diseases. We use high resolution Orbitrap mass spectrometric autoantibody sequencing to track the evolution of a Ro60-specific public clonotypic autoantibody in 4 patients with primary Sjögren's syndrome. This clonotype is specified by a VH3-23/VK3-20 heavy and light chain pairing. Despite apparent stability by conventional immunoassay, analysis of V-region molecular signatures of clonotypes purified from serum samples collected retrospectively over 7years revealed sequential clonal replacement. Prospective longitudinal studies confirmed clonotype loss and replacement at approximately three-monthly intervals. Levels of secreted anti-Ro60 clonotypes fluctuated markedly over time, despite minimal changes in clonal affinity. Our novel findings indicate a relentless turnover of short-lived clonotypic variants, masquerading as long-lived Ro60 humoral autoimmunity.

Neonatal lupus: advances in understanding pathogenesis and identifying treatments of cardiac disease

PURPOSE OF REVIEW

Cardiac manifestations of neonatal lupus include anti-SSA/Ro-SSB/La-mediated conduction system disease and endocardial/myocardial damage resulting in cardiomyopathy. This review will focus on recent data regarding updates on the proposed pathogenesis of disease, morbidity and mortality, and preventive and treatment therapies.

RECENT FINDINGS

Evidence from animal models suggests that reactivity to the p200 region of the Ro52 protein, as well as antibody targeting of L-type calcium channels may be important in the development of cardiac neonatal lupus. In-vitro studies support a protective role of β-2 glycoprotein 1 (prevents anti-Ro binding to apoptotic cells) and pathologic roles of the urokinase-plasminogen activator/receptor system (leads to activation of TGF-β), and endothelin-1 secretion by macrophages in mediating tissue injury. Genetic studies highlight the fetal major histocompatibility complex in the development of disease, and a multigenerational study demonstrates that mothers of neonatal lupus children accumulate genetic risk factors preferentially from the neonatal lupus child's grandparents. Retrospective studies identify demographic and echocardiographic risk factors for morbidity and mortality and address the role of fluorinated steroids, intravenous immunoglobulin and hydroxychloroquine for prevention and treatment of disease.

SUMMARY

Animal studies, in-vitro experiments, genetic analysis and clinical-translational research in cardiac neonatal lupus reveal novel insights and targets for therapy in this often devastating disease.

Umbilical cord blood levels of maternal antibodies reactive with p200 and full-length Ro 52 in the assessment of risk for cardiac manifestations of neonatal lupus

OBJECTIVE

Maternal anti-Ro autoantibodies are associated with cardiac manifestations of neonatal lupus (cardiac NL), yet only 2% of women with this reactivity have an affected child. Identification of a more specific marker would channel intense monitoring to fetuses at greater risk. This study aimed to determine whether autoantibodies against Ro 52 amino acids 200-239 (p200) confer added risk over autoantibodies to full-length Ro 52, Ro 60, or La.

METHODS

Anti-Ro-exposed pregnancies resulting in cardiac NL or no cardiac manifestations were identified from the Research Registry for Neonatal Lupus and the PR Interval and Dexamethasone Evaluation study. Umbilical cord (n = 123) and maternal (n = 115) samples were evaluated by enzyme-linked immunosorbent assay.

RESULTS

The frequencies of p200, Ro 52, Ro 60, and La autoantibodies were not significantly different between affected and unaffected children. However, neonatal anti-Ro 52 and Ro 60 titers were highest in cardiac NL and their unaffected siblings compared to unaffected neonates without a cardiac NL sibling. Although both maternal anti-Ro 52 and p200 autoantibodies were less than 50% specific for cardiac NL, anti-p200 was the least likely of the Ro autoantibodies to be false-positive in mothers who have never had an affected child. Titers of anti-Ro 52 and p200 did not differ during a cardiac NL or unaffected pregnancy from the same mother.

CONCLUSION

Maternal reactivity to p200 does not confer an added risk to fetal conduction defects over full-length Ro 52 or Ro 60 autoantibodies. Mothers who may never be at risk for having an affected child have lower anti-Ro 60 titers and may require less stringent echocardiographic monitoring compared to women with high-titer autoantibodies.

Pathogenicity and proteomic signatures of autoantibodies to Ro and La

Ro/SSA and La/SSB comprise a linked set of autoantigens that are clinically important members of the extractable nuclear antigen family and key translational biomarkers for lupus and primary Sjögren's syndrome. Autoantibodies directed against the Ro60 and La polypeptide components of the Ro/La ribonucleoprotein complex, and the structurally unrelated Ro52 protein, mediate tissue damage in the neonatal lupus syndrome, a model of passively acquired autoimmunity in humans in which the most serious manifestation is congenital heart block (CHB). Recent studies have concentrated on two distinct pathogenic mechanisms by which maternal anti-Ro/La autoantibodies can cause CHB: by forming immune complexes with apoptotic cells in developing fetal heart; and/or by acting as functional autoantibodies that cross-react with and inhibit calcium channels. Although the precise role of the individual autoantibodies is yet to be settled, maternal anti-Ro60 and anti-Ro52 remain the most likely culprits. This article will discuss the molecular pathways that culminate in the development of CHB, including the recent discovery of β2 glycoprotein I as a protective factor, and present a proteomic approach based on direct mass spectrometric sequencing, which may give a more representative snapshot of the idiotype repertoire of these autoantibodies than genomic-based technologies.