Monogenic lupus: Dissecting heterogeneity

Haematopoietic stem cell transplantation for severe autoimmune diseases in children: A review of current literature, registry activity and future directions on behalf of the autoimmune diseases and paediatric diseases working parties of the European Society for Blood and Marrow Transplantation

Although modern clinical management strategies have improved the outcome of paediatric patients with severe autoimmune and inflammatory diseases over recent decades, a proportion will experience ongoing or recurrent/relapsing disease activity despite multiple therapies often leading to irreversible organ damage, and compromised quality of life, growth/development and long-term survival. Autologous and allogeneic haematopoietic stem cell transplantation (HSCT) have been used successfully to induce disease control and often apparent cure of severe treatment-refractory autoimmune diseases (ADs) in children. However, transplant-related outcomes are disease-dependent and long-term outcome data are limited in respect to efficacy and safety. Moreover, balancing risks of HSCT against AD prognosis with continually evolving non-transplant options is challenging. This review appraises published literature on HSCT strategies and outcomes in individual paediatric ADs. We also provide a summary of the European Society for Blood and Marrow Transplantation (EBMT) Registry, where 343 HSCT procedures (176 autologous and 167 allogeneic) have been reported in 326 children (<18 years) for a range of AD indications. HSCT is a promising treatment modality, with potential long-term disease control or cure, but therapy-related morbidity and mortality need to be reduced. Further research is warranted to establish the position of HSCT in paediatric ADs via registries and prospective clinical studies to support evidence-based interspeciality guidelines and recommendations.

DNASE1L3 deficiency, new phenotypes, and evidence for a transient type I IFN signaling

BACKGROUND

Deoxyribonuclease 1 like 3 (DNASE1L3) is a secreted enzyme that has been shown to digest the extracellular chromatin derived from apoptotic bodies, and DNASE1L3 pathogenic variants have been associated with a lupus phenotype. It is unclear whether interferon signaling is sustained in DNASE1L3 deficiency in humans.

OBJECTIVES

To explore interferon signaling in DNASE1L3 deficient patients. To depict the characteristic features of DNASE1L3 deficiencies in human.

METHODS

We identified, characterized, and analyzed five new patients carrying biallelic DNASE1L3 variations. Whole or targeted exome and/or Sanger sequencing was performed to detect pathogenic variations in five juvenile systemic erythematosus lupus (jSLE) patients. We measured interferon-stimulated gene (ISG) expression in all patients. We performed a systematic review of all published cases available from its first description in 2011 to March 24^th 2022.

RESULTS

We identified five new patients carrying biallelic DNASE1L3 pathogenic variations, including three previously unreported mutations. Contrary to canonical type I interferonopathies, we noticed a transient increase of ISGs in blood, which returned to normal with disease remission. Disease in one patient was characterized by lupus nephritis and skin lesions, while four others exhibited hypocomplementemic urticarial vasculitis syndrome. The fourth patient presented also with early-onset inflammatory bowel disease. Reviewing previous reports, we identified 35 additional patients with DNASE1L3 deficiency which was associated with a significant risk of lupus nephritis and a poor outcome together with the presence of anti-neutrophil cytoplasmic antibodies (ANCA). Lung lesions were reported in 6/35 patients.

CONCLUSIONS

DNASE1L3 deficiencies are associated with a broad phenotype including frequently lupus nephritis and hypocomplementemic urticarial vasculitis with positive ANCA and rarely, alveolar hemorrhages and inflammatory bowel disease. This report shows that interferon production is transient contrary to anomalies of intracellular DNA sensing and signaling observed in Aicardi-Goutières syndrome or STING-associated vasculitis in infancy (SAVI).

Characteristics of childhood-onset systemic lupus erythematosus in pregnancy and its association with pregnancy outcomes: a retrospective comparative cohort study

BACKGROUND

Disease situations are more aggressive in patients with childhood-onset systemic lupus erythematosus (cSLE) than in those with adult-onset SLE (aSLE). However, information on pregnant women with cSLE and its association with pregnancy outcomes is limited. This study aimed to compare pregnancies in patients with cSLE vs. aSLE, and further analyse the characteristics of cSLE in pregnant women and explore its association with adverse pregnancy outcomes.

METHODS

Altogether, data of 167 pregnancies from 150 women, including 22 pregnancies with cSLE and 145 pregnancies with aSLE, were retrospectively analysed. Characteristics and disease activity were compared between the cSLE and aSLE groups during pregnancy. Associations between cSLE and the risk of active SLE (SLEPDAI > 4), active lupus nephritis (LN), and adverse pregnancy outcomes were analysed using logistic regression.

RESULTS

The cSLE group had a higher incidence of active SLE (12/22 vs. 30/145, P = 0.001) and active LN (11/22 vs. 26/145, P = 0.001) than the aSLE group. In the multivariable analysis, cSLE was a risk factor for active SLE and active LN during pregnancy, with ORs of 4.742 (95%CI 1.678-13.405, P = 0.003) and 4.652 (95%CI 1.630-13.279, P = 0.004), respectively. No significant association between cSLE and the risk of composite adverse gestational outcomes was identified after sequentially adjusting pre-pregnancy characteristics and pregnancy factors (P > 0.05).

CONCLUSION

Disease activity of women with cSLE in pregnancy was more aggressive than that of women with aSLE, which was similar to the characteristics of non-pregnant women with SLE. cSLE might have indirect effects on the risk of adverse pregnancy outcomes through LN and active disease. Therefore, closely monitoring patients with cSLE during pregnancy is crucial.

Performance of the EULAR/ACR 2019 classification criteria for systemic lupus erythematous in monogenic lupus

OBJECTIVE

To evaluate the application of the EULAR/ACR-2019 criteria to monogenic lupus patients and compare its performance against the SLICC-2012 criteria.

METHODS

In a multicenter retrospective cohort study, consecutive patients with monogenic lupus from three tertiary lupus clinics were enrolled. The diagnosis of monogenic lupus was based on the expert physician's opinion or fulfilling the SLICC-2012 criteria. All enrolled patients had genetic variants. A control group of sporadic childhood SLE (cSLE) and non-SLE patients, were included. A descriptive data analysis was conducted, and the EULAR/ACR-2019 and SLICC-2012 criteria were applied to both groups.

RESULTS

Forty-nine patients with monogenic lupus with a median age at diagnosis of 6.0 (IQR 3.0-10.8) years and 104 controls (55 patients with cSLE and 49 non-lupus patients with a median age at diagnosis of 10.0 and 5.0 respectively) were included. Forty-four (89.8%) patients with monogenic lupus fulfilled the EULAR/ACR-2019 with a mean score of 22.3±8.9. The most frequent domains were immunologic (93.9%), musculoskeletal and renal (each 57.1%), and mucocutaneous (55.1%). Fifty-four (98.2%) cSLE patients and six (12.2%) non-lupus patients met the EULAR/ACR-2019 criteria with a mean score of 22.5±9.2 and 8.5±5.2, respectively. The sensitivity of the EULAR/ACR-2019 criteria in monogenic lupus was 89.9% (95% CI: 78.3-90.2), while the specificity was 87.6% (95% CI: 75.2-88.7).

CONCLUSION

This is the first and largest cohort of monogenic lupus patients testing the performance of the 2019-EULAR/ACR criteria. It efficiently classifies monogenic lupus patients, irrespective of the underlying genetic variants. Further studies are needed before these criteria are adopted worldwide. Key Points • Typically, patients with monogenic lupus have early onset severe disease, especially with mucocutaneous manifestations and a strong family history of SLE. • Monogenic lupus is a distinctive entity and might differ from the sporadic childhood SLE. • Our study includes a large multinational cohort of monogenic lupus with heterogeneous phenotypic features and underlying genetic variants. • Our study demonstrates that the EULAR/ACR-2019 criteria efficiently classified monogenic lupus patients, irrespective of the diversity of the underlying genetic variants.

DNMT3B (rs2424913) polymorphism is associated with systemic lupus erythematosus alone and with co-existing periodontitis in a Brazilian population

The association between Periodontitis and Systemic Lupus Erythematosus (SLE) has been primarily based on their similar pathophysiology and both are associated with genetic polymorphisms.

OBJECTIVES

To investigate an association between the methylation-related gene polymorphisms DNMT3B (rs2424913) and MTHFR (rs1801133) to Systemic Lupus Erythematosus (SLE) and Periodontitis.

METHODOLOGY

In total, 196 individuals of all genders aged 24 to 60 years old were allocated into four groups based on their systemic and periodontal status, namely: Healthy control (n=60), periodontitis (n=51), SLE (n=47), and SLE + periodontitis (n=38). Individuals with SLE were stratified according to disease activity (SLEDAI) in inactive or active. We performed polymorphism analysis using PCR-RFLP with genomic DNA from mouthwash. We analyzed data using Fisher's Exact, Chi-square test, and regression models.

RESULTS

Periodontal status were similar in subjects with periodontitis alone and combined with SLE. SLE patients with periodontitis had a longer SLE diagnosis than SLE only (p=0.001). For DNMT3 B polymorphism, the periodontitis, SLE, and Inactive SLE + periodontitis groups showed a higher frequency of T allele and TT genotypes compared to healthy controls (p<0.05). Regression analyses showed that the TT genotype is a strong risk factor for periodontitis (OR=4.53; CI95%=1.13-18.05) and also for SLE without periodontitis (OR=11.57; CI95%=3.12-42.84) and SLE with periodontitis (OR=5.27; CI95%=1.25-22.11) when compared to control.

CONCLUSION

SLE patients with periodontitis had a longer length of SLE diagnosis. The DNMT3B (rs2424913) polymorphism was associated with periodontitis and SLE alone or combined with periodontitis. Our study contributes to understanding the genetic mechanisms involved in periodontitis and SLE susceptibility.

A glimpse into the future of systemic lupus erythematosus

This viewpoint article on a forecast of clinically meaningful changes in the management of systemic lupus erythematosus (SLE) in the next 10 years is based on a review of the current state of the art. The groundwork has been laid by a robust series of classification criteria and treatment recommendations that have all been published since 2019. Building on this strong foundation, SLE management predictably will take significant steps forward. Assessment for lupus arthritis will presumably include musculoskeletal sonography. Large-scale polyomics studies are likely to unravel more of the central immune mechanisms of the disease. Biomarkers predictive of therapeutic success may enter the field; the type I interferon signature, as a companion for use of anifrolumab, an antibody against the common type I interferon receptor, is one serious candidate. Besides anifrolumab for nonrenal SLE and the new calcineurin inhibitor voclosporin in lupus nephritis, both of which are already approved in the United States and likely to become available in the European Union in 2022, several other approaches are in advanced clinical trials. These include advanced B cell depletion, inhibition of costimulation via CD40 and CD40 ligand (CD40L), and Janus kinase 1 (Jak1) and Tyrosine kinase 2 (Tyk2) inhibition. At the same time, essentially all of our conventional therapeutic armamentarium will continue to be used. The ability of patients to have successful SLE pregnancies, which has become much better in the last decades, should further improve, with approaches including tumor necrosis factor blockade and self-monitoring of fetal heart rates. While we hope that the COVID-19 pandemic will soon be controlled, it has highlighted the risk of severe viral infections in SLE, with increased risk tied to certain therapies. Although there are some data that a cure might be achievable, this likely will remain a challenge beyond 10 years from now.

Druggable monogenic immune defects hidden in diverse medical specialties: Focus on overlap syndromes

In the last two decades two new paradigms changed our way of perceiving primary immunodeficiencies: An increasing number of immune defects are more associated with inflammatory or autoimmune features rather than with infections. Some primary immune defects are due to hyperactive pathways that can be targeted by specific inhibitors, providing innovative precision treatments that can change the natural history of diseases. In this article we review some of these "druggable" inborn errors of immunity and describe how they can be suspected and diagnosed in diverse pediatric and adult medicine specialties. Since the availability of precision treatments can dramatically impact the course of these diseases, preventing the development of organ damage, it is crucial to widen the awareness of these conditions and to provide practical hints for a prompt detection and cure.

Systemic lupus erythematosus as a genetic disease

Systemic lupus erythematosus is the prototypical systemic autoimmune disease, as it is characterized both by protean multi-organ system manifestations and by the uniform presence of pathogenic autoantibodies directed against components of the nucleus. Prior to the modern genetic era, the diverse clinical manifestations of SLE suggested to many that SLE patients were unlikely to share a common genetic risk basis. However, modern genetic studies have revealed that SLE usually arises when an environmental exposure occurs in an individual with a collection of genetic risk variants passing a liability threshold. Here, we summarize the current state of the field aimed at: (1) understanding the genetic architecture of this complex disease, (2) synthesizing how this genetic risk architecture impacts cellular and molecular disease pathophysiology, (3) providing illustrative examples that highlight the rich complexity of the pathobiology of this prototypical autoimmune disease and (4) communicating this complex etiopathogenesis to patients.

[When to consider type I interferonopathy in adulthood?]

Type I interferonopathies (IP1) are a heterogeneous group of Mendelian diseases characterized by overactivation of the type I interferon (IFN) pathway. They are caused by monogenic (rarely digenic) mutations of proteins involved in this key pathway of innate immunity. IP1 transmission can be dominant, recessive or X-linked and penetrance differs from one IP1 to another. The clinical spectrum is broad and mainly includes central nervous system involvement with calcifications of the basal ganglia, skin disorders such as cutaneous vasculitis that can be mutilating. Joint disorders including non-destructive deforming arthropathy, pulmonary involvement such as intra-alveolar haemorrhage or interstitial lung disease, and haematological symptoms with cytopenia and/or immune deficiency are also seen. The clinical manifestations vary from one IP1 to another and their spectrum is constantly expanding along with the description of new IP1s and patients. The inflammatory syndrome is generally mild and autoimmune stigmata are frequently found. Almost all patients display overexpression of the type I IFN pathway detected, for instance, by the evaluation of IFN-stimulated genes expression, referred as "interferon signature". The related morbidity and mortality are high. However, the beneficial effect on certain symptoms of targeted therapies inhibiting type I IFN, such as JAK inhibitors, has led to a promising improvement in the management of these patients.

"P2RY8-son" break of tolerance promotes SLE

In this issue of JEM, He et al. (2021. J. Exp. Med.https://doi.org/10.1084/jem.20211004) associate novel P2RY8 genetic variants to lupus, expanding the field of monogenic autoimmunity. The authors demonstrate that P2RY8 prevents the expansion of DNA-reactive B cells by restraining B cell mobility and activation within the germinal center.

P2RY8 variants in lupus patients uncover a role for the receptor in immunological tolerance

B cell self-tolerance is maintained through multiple checkpoints, including restraints on intracellular signaling and cell trafficking. P2RY8 is a receptor with established roles in germinal center (GC) B cell migration inhibition and growth regulation. Somatic P2RY8 variants are common in GC-derived B cell lymphomas. Here, we identify germline novel or rare P2RY8 missense variants in lupus kindreds or the related antiphospholipid syndrome, including a "de novo" variant in a child with severe nephritis. All variants decreased protein expression, F-actin abundance, and GPCR-RhoA signaling, and those with stronger effects increased AKT and ERK activity and cell migration. Remarkably, P2RY8 was reduced in B cell subsets from some SLE patients lacking P2RY8 gene variants. Low P2RY8 correlated with lupus nephritis and increased age-associated B cells and plasma cells. By contrast, P2RY8 overexpression in cells and mice restrained plasma cell development and reinforced negative selection of DNA-reactive developing B cells. These findings uncover a role of P2RY8 in immunological tolerance and lupus pathogenesis.

Impaired respiratory burst contributes to infections in PKCδ-deficient patients

Patients with autosomal recessive protein kinase C δ (PKCδ) deficiency suffer from childhood-onset autoimmunity, including systemic lupus erythematosus. They also suffer from recurrent infections that overlap with those seen in patients with chronic granulomatous disease (CGD), a disease caused by defects of the phagocyte NADPH oxidase and a lack of reactive oxygen species (ROS) production. We studied an international cohort of 17 PKCδ-deficient patients and found that their EBV-B cells and monocyte-derived phagocytes produced only small amounts of ROS and did not phosphorylate p40phox normally after PMA or opsonized Staphylococcus aureus stimulation. Moreover, the patients' circulating phagocytes displayed abnormally low levels of ROS production and markedly reduced neutrophil extracellular trap formation, altogether suggesting a role for PKCδ in activation of the NADPH oxidase complex. Our findings thus show that patients with PKCδ deficiency have impaired NADPH oxidase activity in various myeloid subsets, which may contribute to their CGD-like infectious phenotype.

Erythroid mitochondrial retention triggers myeloid-dependent type I interferon in human SLE

Emerging evidence supports that mitochondrial dysfunction contributes to systemic lupus erythematosus (SLE) pathogenesis. Here we show that programmed mitochondrial removal, a hallmark of mammalian erythropoiesis, is defective in SLE. Specifically, we demonstrate that during human erythroid cell maturation, a hypoxia-inducible factor (HIF)-mediated metabolic switch is responsible for the activation of the ubiquitin-proteasome system (UPS), which precedes and is necessary for the autophagic removal of mitochondria. A defect in this pathway leads to accumulation of red blood cells (RBCs) carrying mitochondria (Mito+ RBCs) in SLE patients and in correlation with disease activity. Antibody-mediated internalization of Mito+ RBCs induces type I interferon (IFN) production through activation of cGAS in macrophages. Accordingly, SLE patients carrying both Mito+ RBCs and opsonizing antibodies display the highest levels of blood IFN-stimulated gene (ISG) signatures, a distinctive feature of SLE.

Monogenic Lupus with IgA Nephropathy Caused by Spondyloenchondrodysplasia with Immune Dysregulation

Monogenic disorders causing systemic lupus erythematosus represent a small subset of cases. Type-1 interferonopathies, like spondyloenchondrodysplasia with immune dysregulation constitute an important functional category of monogenic lupus. Apart from autoimmune disorders, neurological and skeletal abnormalities are additional manifestations observed in this disorder. A young female presented with seizures due to acute hemorrhagic stroke secondary to malignant hypertension. On evaluating the cause for hypertension, there was evidence of glomerulonephritis and multiple autoantibodies positivity including dsDNA. A diagnosis of lupus was made based on clinical and laboratory findings. Kidney biopsy revealed mesangial proliferative glomerulonephritis with predominant IgA deposits favouring IgA nephropathy. Additional features in the form of short stature with vertebral abnormalities and bilateral basal ganglia calcification led to evaluation of Type-1 interferonopathies. Sanger sequencing identified a novel compound heterozygous variants c.550C>T (p.Q184*) in exon 3 and c.740T>G (p.L247R) in exon 4 of ACP5 gene. Parents were found to be carriers of the variants in ACP5 gene. Management included antihypertensive agents and symptomatic therapy. On follow-up, there was complete resolution of glomerulonephritis and normalization of blood pressure. This case report documents the classic phenotype comprising autoimmune, skeletal, and neurological abnormalities in spondyloenchondrodysplasia with immune dysregulation with a novel variant on Sanger sequencing in an Indian patient. This report also highlights the rare coexistence of IgA nephropathy in monogenic lupus.

Hidden mysteries behind genome, epigenome, and exposome of lupus erythematosus

As an extremely heterogeneous disease, lupus erythematosus (LE) occurs when a genetically susceptible individual encounters specific environmental triggers. Epigenetics bridges genetics and environment and helps explain their interactions. Comprehensively understanding the hidden mysteries behind the genome, epigenome, and exposome of lupus could contribute to precision prevention and treatment of lupus.

Monogenic lupus due to DNASE1L3 deficiency in a pediatric patient with urticarial rash, hypocomplementemia, pulmonary hemorrhage, and immune-complex glomerulonephritis

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease and usually involves the skin, musculoskeletal system, and kidneys. More than 30 genes have been to monogenic lupus, so far. Monogenic lupus is often characterized by an early-onset, similar family history, and syndromic appearance. Herein we present a pediatric patient with DNASE1L3 deficiency, suffering from both urticarial skin lesions, recurrent hemoptysis, and renal involvement, eventually diagnosed as this rare monogenic lupus. The patient suffered from recurrent urticarial rash and hemoptysis since the age of 15 months of age. He had microscopic hematuria, mild proteinuria, hypocomplementemia, and positive antinuclear antibody, anti-dsDNA, and antineutrophil cytoplasmic antibodies. Renal biopsy yielded immunocomplex glomerulonephritis. Due to early-onset, similar sibling history and consanguineous parents, we suspected monogenic lupus and performed whole-exome sequencing, which further revealed a homozygous T97Ifs*2 mutation (NM_004944.4: c.290_291delCA/p.Thr97Ilefs*2) in DNASE1L3 gene. In conclusion, DNASE1L3 deficiency should be thought when juvenile SLE occurs with early disease-onset, pulmonary hemorrhage, glomerulonephritis, and recurrent urticarial rash along with ANCA positivity.

Monogenic Autoinflammatory Diseases: State of the Art and Future Perspectives

Systemic autoinflammatory diseases are a heterogeneous family of disorders characterized by a dysregulation of the innate immune system, in which sterile inflammation primarily develops through antigen-independent hyperactivation of immune pathways. In most cases, they have a strong genetic background, with mutations in single genes involved in inflammation. Therefore, they can derive from different pathogenic mechanisms at any level, such as dysregulated inflammasome-mediated production of cytokines, intracellular stress, defective regulatory pathways, altered protein folding, enhanced NF-kappaB signalling, ubiquitination disorders, interferon pathway upregulation and complement activation. Since the discover of pathogenic mutations of the pyrin-encoding gene MEFV in Familial Mediterranean Fever, more than 50 monogenic autoinflammatory diseases have been discovered thanks to the advances in genetic sequencing: the advent of new genetic analysis techniques and the discovery of genes involved in autoinflammatory diseases have allowed a better understanding of the underlying innate immunologic pathways and pathogenetic mechanisms, thus opening new perspectives in targeted therapies. Moreover, this field of research has become of great interest, since more than a hundred clinical trials for autoinflammatory diseases are currently active or recently concluded, allowing us to hope for considerable acquisitions for the next few years. General paediatricians need to be aware of the importance of this group of diseases and they should consider autoinflammatory diseases in patients with clinical hallmarks, in order to guide further examinations and refer the patient to a specialist rheumatologist. Here we resume the pathogenesis, clinical aspects and diagnosis of the most important autoinflammatory diseases in children.

Histologic Patterns and Clues to Autoinflammatory Diseases in Children: What a Cutaneous Biopsy Can Tell Us

Autoinflammation is defined by aberrant, antigen-independent activation of the innate immune signaling pathways. This leads to increased, pro-inflammatory cytokine expression and subsequent inflammation. In contrast, autoimmune and allergic diseases are antigen-directed immune responses from activation of the adaptive immune system. The innate and adaptive immune signaling pathways are closely interconnected. The group of 'complex multigenic diseases' are a result of mutual dysregulation of both the autoinflammatory and autoimmune physiologic components. In contrast, monogenic autoinflammatory syndromes (MAIS) result from single mutations and are exclusively autoinflammatory in their pathogenesis. Studying the clinical and histopathological findings for the various MAIS explains the phenotypical correlates of their specific mutations. This review aims to group the histopathologic clues for autoinflammation into three recognizable patterns. The presence of these histologic patterns in a pediatric patient with recurrent fevers and systemic inflammation should raise suspicion of an autoinflammatory component in MAIS, or, more frequently, in a complex multigenic disease. The three major histopathological patterns seen in autoinflammation are as follows: (i) the 'neutrophilic' pattern, seen in urticarial neutrophilic dermatosis, pustular psoriasis, aseptic neutrophilic folliculitis, and Sweet's syndrome; (ii) the 'vasculitic' pattern seen in small vessel-vasculitis (including hypersensitivity/leukocytoclastic vasculitis, thrombosing microangiopathy and lymphocytic vasculitis), and intermediate-sized vessel vasculitis, mimicking polyarteritis nodosa; and (iii) the 'granulomatous' pattern. Beyond these three patterns, there are additional histopathologic clues, which are detailed below. It is important for a dermatopathologist to recognize the patterns of autoinflammation, so that a diagnosis of MAIS or complex multigenic diseases may be obtained. Finally, careful histopathologic analyses could contribute to a better understanding of the various clinical manifestations of autoinflammation.

Type I Interferonopathies in Children: An Overview

Notable advances in gene sequencing methods in recent years have permitted enormous progress in the phenotypic and genotypic characterization of autoinflammatory syndromes. Interferonopathies are a recent group of inherited autoinflammatory diseases, characterized by a dysregulation of the interferon pathway, leading to constitutive upregulation of its activation mechanisms or downregulation of negative regulatory systems. They are clinically heterogeneous, but some peculiar clinical features may lead to suspicion: a familial "idiopathic" juvenile arthritis resistant to conventional treatments, an early necrotizing vasculitis, a non-infectious interstitial lung disease, and a panniculitis associated or not with a lipodystrophy may represent the "interferon alarm bells." The awareness of this group of diseases represents a challenge for pediatricians because, despite being rare, a differential diagnosis with the most common childhood rheumatological and immunological disorders is mandatory. Furthermore, the characterization of interferonopathy molecular pathogenetic mechanisms is allowing important steps forward in other immune dysregulation diseases, such as systemic lupus erythematosus and inflammatory myositis, implementing the opportunity of a more effective target therapy.

Complement C4A Regulates Autoreactive B Cells in Murine Lupus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease mediated by pathogenic autoantibodies. While complement protein C4 is associated with SLE, its isoforms (C4A and C4B) are not equal in their impact. Despite being 99% homologous, genetic studies identified C4A as more protective than C4B. By generating gene-edited mouse strains expressing either human C4A or C4B and crossing these with the 564lgi lupus strain, we show that, overall, C4A-like 564Igi mice develop less humoral autoimmunity than C4B-like 564Igi mice. This includes a decrease in the number of GCs, autoreactive B cells, autoantibodies, and memory B cells. The higher efficiency of C4A in inducing self-antigen clearance is associated with the follicular exclusion of autoreactive B cells. These results explain how the C4A isoform is protective in lupus and suggest C4A as a possible replacement therapy in lupus.

Simoni et al. address a long-standing question about how complement C4A and C4B isoforms differ in function in vivo in autoimmunity. They find that C4A leads to an increased protection in humoral autoimmunity relative to C4B. Autoantibody diversity is likewise dependent on the C4 protein isotype.

Basophils and Systemic Lupus Erythematosus in Murine Models and Human Patients

Basophils are the rarest cell population in the blood. Even though basophils are known to participate in some allergic reactions and immune responses to parasitic infections, their immunological role is still largely elusive. Recent evidence has suggested that in some murine models of systemic lupus erythematosus and lupus-like nephritis, basophils may also be implicated in autoimmunity processes by promoting autoantibody production and tissue injury. We conducted a systematic search to collect the available evidence on basophils' potential immunomodulatory role in autoimmunity and, particularly, systemic lupus erythematosus. We identified several articles investigating basophils' role in murine models of lupus (n = 3) and in patients affected with systemic lupus erythematosus (n = 8). Even though the alteration of the "adaptive" immune response is considered the main immunopathological event in systemic lupus erythematosus, the contribution from the mechanisms of "innate" immunity and, particularly, basophils may be relevant as well, by modulating the activation, polarization, and survival of lymphocytes.

Efficacy of a sequential treatment by belimumab in monogenic systemic lupus erythematosus

The objective of the study was to report the safety and potential therapeutic effect of belimumab in monogenic systemic lupus erythematosus (SLE). Consecutive children with monogenic SLE treated with belimumab were evaluated retrospectively. Response parameters assessment was completed at the time of initiation of belimumab, at 6 months, and last follow-up visit. Response parameters comprised physician global assessment (physician GA) and parent global assessment (parent GA), global disease activity as measured by SLE disease activity index (SLEDAI), and daily glucocorticoids dose. Undesirable events affecting patients during treatment were also collected. Six children with monogenic SLE proved by genetic testing (five patients with C1q deficiency and one patient with deoxyribonuclease II (DNase II) deficiency), failed glucocorticoids and sequential immunosuppressive medications. Belimumab was added to glucocorticoids and current immunosuppressive medications. The main indications for belimumab initiation were mucocutaneous disease, arthritis, and inability to taper glucocorticoids. All patients tolerated belimumab infusion. No serious events were reported. However, one patient was lost to follow-up and died because of sepsis. Compared to the baseline values, there was an improvement in physician GA, parent GA, and SLEDAI, and a notable reduction in the need of daily corticosteroids. However, there were no significant changes in the complement and ds-DNA antibody levels. Belimumab can be considered as an adjunctive therapeutic option for patients with refractory monogenic SLE. Further follow-up and more patients needed to confirm this finding and a larger prospective study is required for more definitive conclusions.

Mapping systemic lupus erythematosus heterogeneity at the single-cell level

Patients with systemic lupus erythematosus (SLE) display a complex blood transcriptome whose cellular origin is poorly resolved. Using single-cell RNA sequencing, we profiled ~276,000 peripheral blood mononuclear cells from 33 children with SLE with different degrees of disease activity and 11 matched controls. Increased expression of interferon-stimulated genes (ISGs) distinguished cells from children with SLE from healthy control cells. The high ISG expression signature (ISGhi) derived from a small number of transcriptionally defined subpopulations within major cell types, including monocytes, CD4+ and CD8+ T cells, natural killer cells, conventional and plasmacytoid dendritic cells, B cells and especially plasma cells. Expansion of unique subpopulations enriched in ISGs and/or in monogenic lupus-associated genes classified patients with the highest disease activity. Profiling of ~82,000 single peripheral blood mononuclear cells from adults with SLE confirmed the expansion of similar subpopulations in patients with the highest disease activity. This study lays the groundwork for resolving the origin of the SLE transcriptional signatures and the disease heterogeneity towards precision medicine applications.

Systemic lupus erythematosus in a girl with PTEN variant and transaldolase deficiency: a novel phenotype

Genetic defect of phosphatase and tensin homolog (PTEN) gene might play a role in B cell hyperactivity and result in the development of systemic lupus erythematosus (SLE), while transaldolase deficiency has a spectrum of clinical features including autoimmune endocrinopathy. Herein, we identified a novel phenotype in a girl presenting with clinical and laboratory findings consistent with SLE. Exome sequencing identified pathogenic heterozygous variant in PTEN gene (NM_000314: exon 6: c.518G > C: p. R173P) and homozygous variant in TALDO1 gene (NM_006755: exon 6: c.793C del: p. Q265f). Our report highlights the association of PTEN mutation and autoimmunity and the possibility that transaldolase deficiency may be indirectly involved in the development of SLE.

Systemic Lupus Erythematosus

Systemic lupus erythematosus (lupus) is characterized by aberrant activity of the immune system, leading to variable clinical symptoms. Lupus is more prevalent in African American women and women in other ethnic minority groups. Diagnosing, treating, and identifying novel therapies for lupus is challenging because of its genetic and phenotypic heterogeneity. Lupus nephritis is the most common target-organ manifestation and requires individualized care to minimize toxicity. A multidisciplinary approach to caring for pregnant patients with lupus is essential to optimize outcomes.

Refractory secondary thrombotic microangiopathy with kidney injury associated with systemic lupus erythematosus in a pediatric patient

Thrombotic microangiopathy (TMA) is generally diagnosed through clinical features characterized as microangiopathic hemolytic anemia, thrombocytopenia, and multiple organ injury, as well as by pathological findings such as vascular damage and endothelial cell injury. Rheumatic and autoimmune diseases could be accompanied by secondary TMA; in fact, systemic lupus erythematosus (SLE) is a common disease associated with secondary TMA, and SLE complicated with TMA has been reported to have a poor prognosis. Although TMA occurs rarely in pediatric SLE patients, it often leads to severe clinical conditions. Here, we report a rare case of severe juvenile-onset SLE complicated with TMA and kidney injury. The 5-year-old patient showed renal dysfunction, thrombocytopenia, hemolytic anemia, nephrotic syndrome, hypocomplementemia, and elevation of anti-dsDNA IgG levels. Kidney biopsy revealed mesangial proliferation and endocapillary proliferation, as well as plumped endothelial cells, with full-house pattern deposits in immunofluorescence study. Combination treatment of methylprednisolone pulse therapy followed by oral prednisolone, mycophenolate mofetil, and plasma exchange was effective, whereas eculizumab did not show therapeutic effects. The patient further showed recurrent deterioration, and we initiated intravenous cyclophosphamide in addition to combination treatment and eventually succeeded in controlling the disease. Genome analysis by whole-exome sequencing revealed no particular gene mutation related to either complement disorders or type-1 interferon. Further elucidations concerning the pathogenic mechanisms causing juvenile-onset SLE are needed to establish an efficient treatment strategy for TMA with SLE.

Inflammatory markers in systemic lupus erythematosus

While systemic lupus erythematosus (SLE) is an autoantibody and immune complex disease by nature, most of its organ manifestations are in fact inflammatory. SLE activity scores thus heavily rely on assessing inflammation in the various organs. This focus on clinical items demonstrates that routine laboratory markers of inflammation are still limited in their impact. The erythrocyte sedimentation rate (ESR) is used, but represents a rather crude overall measure. Anemia and diminished serum albumin play a role in estimating inflammatory activity, but both are reflecting more than one mechanism, and the association with inflammation is complex. C-reactive protein (CRP) is a better marker for infections than for SLE activity, where there is only a limited association, and procalcitonin (PCT) is also mainly used for detecting severe bacterial infection. Of the cytokines directly induced by immune complexes, type I interferons, interleukin-18 (IL-18) and tumor necrosis factor (TNF) are correlated with inflammatory disease activity. Still, precise and timely measurement is an issue, which is why they are not currently used for routine purposes. While somewhat more robust in the assays, IL-18 binding protein (IL-18BP) and soluble TNF-receptor 2 (TNF-R2), which are related to the respective cytokines, have not yet made it into clinical routine. The same is true for several chemokines that are increased with activity and relatively easy to measure, but still experimental parameters. In the urine, proteinuria leads and is essential for assessing kidney involvement, but may also result from damage. Similar to the situation in serum and plasma, several cytokines and chemokines perform reasonably well in scientific studies, but are not routine parameters. Cellular elements in the urine are more difficult to assess in the routine laboratory, where sufficient routine is not always available. Therefore, the analysis of urinary T cells may have potential for better monitoring renal inflammation.