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Pyogenic liver abscess is an uncommon pediatric condition, and represents a rare causative agent in otherwise healthy children. Such infections may signal an underlying inborn error of immunity. Alpha-1 antitrypsin (A1AT), encoded by the gene, is a serine protease inhibitor with key immunomodulatory functions. In mouse models, A1AT prevents degradation of the antimicrobial SPLUNC1 protein to enhance host defense against . In humans, while A1AT variants can be associated with a generally increased risk of respiratory infection, to our knowledge no corresponding impact with respect to has been reported. We report a previously healthy 14-month-old girl who developed liver abscess without identifiable predisposing factors. Comprehensive immunologic evaluation was unremarkable except for whole exome sequencing revealing homozygous S allele pathogenic variant (c.863 A>T, p.E288V) known as the S allele associated with partial A1AT deficiency. The clinical presentation, microbiologic findings, and disease course suggested that defective A1AT function may have contributed to dysregulated inflammation and susceptibility to infection. This case highlights a potential association between homozygosity in the pathogenic S variant of and susceptibility to severe , in this case liver abscess. While A1AT deficiency is classically associated with pulmonary and hepatic disease, the immunomodulatory role of A1AT suggests broader relevance in host defense. Early recognition of underlying defects in children with unusual or severe infections may inform prognosis, guide management, and prompt appropriate genetic counseling and surveillance for long-term complications.

In response to inflammatory stimuli, dendritic cells (DCs) trigger the process of maturation, a terminal differentiation program required to initiate T-lymphocyte responses. A hallmark of maturation is downregulation of endocytosis, which is widely assumed to restrict the ability of mature DCs to capture and present antigens encountered after the initial stimulus. We found that mature DCs continue to accumulate antigens, especially by receptor-mediated endocytosis and phagocytosis. Internalized antigens are transported normally to late endosomes and lysosomes, loaded onto MHC class II molecules (MHCII), and then presented efficiently to T cells. This occurs despite the fact that maturation results in the general depletion of MHCII from late endocytic compartments, with MHCII enrichment being typically thought to be a required feature of antigen processing and peptide loading compartments. Internalized antigens can also be cross-presented on MHC class l molecules, without any reduction in efficiency relative to immature DCs. Thus, although mature DCs markedly downregulate their capacity for macropinocytosis, they continue to capture, process, and present antigens internalized via endocytic receptors, suggesting that they may continuously initiate responses to newly encountered antigens during the course of an infection.

CBL-B is an E3 ubiquitin ligase that ubiquitinates proteins downstream of immune receptors to downregulate positive signaling cascades. Distinct homozygous mutations in CBLB were identified in 3 unrelated children with early-onset autoimmunity, one of whom also had chronic urticaria. Patient T cells exhibited hyperproliferation in response to anti- CD3 cross-linking. One of the mutations, p.R496X, abolished CBL-B expression, and a second mutation, p.C464W, resulted in preserved CBL-B expression. The third mutation, p.H285L in the SH2 domain of CBL-B, was expressed at half the normal level in the patient's cells. Mice homozygous for the CBL-B p.H257L mutation, which corresponds to the patient's p.H285L mutation, had T and B cell hyperproliferation in response to antigen receptor cross-linking. [Cblb.sup.H257L] mice had increased percentages of T regulatory cells (Tregs) that had normal in vitro suppressive function. However, T effector cells from the patient with the p.H285L mutation and [Cblb.sup.H257L] mice were resistant to suppression by WT Tregs. Bone marrow- derived mast cells from [Cblb.sup.H257L] mice were hyperactivated after Fc[epsilon]RI cross-linking, and [Cblb.sup.H257L] mice demonstrated exaggerated IgE-mediated passive anaphylaxis. This study establishes CBL-B deficiency as a cause of immune dysregulation.

We have used magnetic resonance imaging (MRI) to provide important new insights into the function of the human placenta in utero. We have measured slow net flow and high net oxygenation in the placenta in vivo, which are consistent with efficient delivery of oxygen from mother to fetus. Our experimental evidence substantiates previous hypotheses on the effects of spiral artery remodelling in utero and also indicates rapid venous drainage from the placenta, which is important because this outflow has been largely neglected in the past. Furthermore, beyond Braxton Hicks contractions, which involve the entire uterus, we have identified a new physiological phenomenon, the 'utero-placental pump', by which the placenta and underlying uterine wall contract independently of the rest of the uterus, expelling maternal blood from the intervillous space.

BACKGROUNDPediatric SARS-CoV-2 infection can be complicated by a dangerous hyperinflammatory condition termed multisystem inflammatory syndrome in children (MIS-C). The clinical and immunologic spectrum of MIS-C and its relationship to other inflammatory conditions of childhood have not been studied in detail.METHODSWe retrospectively studied confirmed cases of MIS-C at our institution from March to June 2020. The clinical characteristics, laboratory studies, and treatment response were collected. Data were compared with historic cohorts of Kawasaki disease (KD) and macrophage activation syndrome (MAS).RESULTSTwenty-eight patients fulfilled the case definition of MIS-C. Median age at presentation was 9 years (range: 1 month to 17 years); 50% of patients had preexisting conditions. All patients had laboratory confirmation of SARS-CoV-2 infection. Seventeen patients (61%) required intensive care, including 7 patients (25%) who required inotrope support. Seven patients (25%) met criteria for complete or incomplete KD, and coronary abnormalities were found in 6 cases. Lymphopenia, thrombocytopenia, and elevation in inflammatory markers, D-dimer, B-type natriuretic peptide, IL-6, and IL-10 levels were common but not ubiquitous. Cytopenias distinguished MIS-C from KD and the degree of hyperferritinemia and pattern of cytokine production differed between MIS-C and MAS. Immunomodulatory therapy given to patients with MIS-C included intravenous immune globulin (IVIG) (71%), corticosteroids (61%), and anakinra (18%). Clinical and laboratory improvement were observed in all cases, including 6 cases that did not require immunomodulatory therapy. No mortality was recorded in this cohort.CONCLUSIONMIS-C encompasses a broad phenotypic spectrum with clinical and laboratory features distinct from KD and MAS.FUNDINGThis work was supported by the National Institutes of Health, National Institute of Arthritis and Musculoskeletal and Skin Diseases; the National Institute of Allergy and Infectious Diseases; Rheumatology Research Foundation Investigator Awards and Medical Education Award; Boston Children's Hospital Faculty Career Development Awards; the McCance Family Foundation; and the Samara Jan Turkel Center.

Background Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) were historically thought to be distinct entities, often managed in isolation. In fact, these conditions are closely related. A collaborative approach, which incorporates expertise from subspecialties that previously treated HLH/MAS independently, is needed. We leveraged quality improvement (QI) techniques in the form of an Evidence-Based Guideline (EBG) to build consensus across disciplines on the diagnosis and treatment of HLH/MAS. Methods A multidisciplinary work group was convened that met monthly to develop the HLH/MAS EBG. Literature review and expert opinion were used to develop a management strategy for HLH/MAS. The EBG was implemented, and quality metrics were selected to monitor outcomes. Results An HLH/MAS clinical team was formed with representatives from subspecialties involved in the care of patients with HLH/MAS. Broad entry criteria for the HLH/MAS EBG were established and included fever and ferritin ≥500 ng/mL. The rheumatology team was identified as the “gate-keeper,” charged with overseeing the diagnostic evaluation recommended in the EBG. First-line medications were recommended based on the acuity of illness and risk of concurrent infection. Quality metrics to be tracked prospectively based on time to initiation of treatment and clinical response were selected. Conclusion HLH/MAS are increasingly considered to be a spectrum of related conditions, and joint management across subspecialties could improve patient outcomes. Our experience in creating a multidisciplinary approach to HLH/MAS management can serve as a model for care at other institutions.

In atopic dermatitis (AD), skin barrier and immune dysfunction result in chronic tissue inflammation, yet our understanding of the tissue ecosystem remains incomplete. Here, we generate a multi-modal census of 280,518 cells from whole skin tissue samples from 17 adults, including 11 AD patients, integrating it with 430,186 cell profiles from four previous studies into a comprehensive human skin cell atlas. Reconstruction of keratinocyte differentiation revealed disrupted cornification in AD associated with signals from an immune and stromal multicellular community – comprising MMP12 + and migratory dendritic cells (DCs), cycling innate lymphoid cells (ILC), natural killer cells, inflammatory CCL19 + IL4I1 + fibroblasts, and clonally expanded IL13 + IL22 + IL26 + T cells connected by intercellular feedback loops predicted to impact community assembly. Subsets from this community, along with disrupted cornified keratinocytes, were enriched in GWAS, suggesting that dysfunction in this communication network may initiate AD. Our work highlights disease-associated cell subsets and interactions in chronic skin inflammation. In atopic dermatitis (AD), skin barrier disruption leads to chronic inflammation. Here, the authors use single-cell sequencing to map human skin, uncovering AD-specific cell states and populations involved in immune responses and cell differentiation.

The coat protein I (COPI) complex mediates retrograde trafficking from the Golgi to the endoplasmic reticulum (ER). Five siblings with persistent bacterial and viral infections and defective humoral and cellular immunity had a homozygous p.K652E mutation in the γ1 subunit of COPI (γ1-COP). The mutation disrupts COPI binding to the KDEL receptor and impairs the retrieval of KDEL-bearing chaperones from the Golgi to the ER. Homozygous Copg1K652E mice had increased ER stress in activated T and B cells, poor antibody responses, and normal numbers of T cells that proliferated normally, but underwent increased apoptosis upon activation. Exposure of the mutants to pet store mice caused weight loss, lymphopenia, and defective T cell proliferation that recapitulated the findings in the patients. The ER stress-relieving agent tauroursodeoxycholic acid corrected the immune defects of the mutants and reversed the phenotype they acquired following exposure to pet store mice. This study establishes the role of γ1-COP in the ER retrieval of KDEL-bearing chaperones and thereby the importance of ER homeostasis in adaptive immunity.

Background Sweet syndrome (SS), also known as acute febrile neutrophilic dermatosis, is an immunologic syndrome characterized by widespread neutrophilic infiltration. Histiocytoid Sweet syndrome (H-SS) is a histopathologic variant of SS. While SS most commonly occurs in adults, this case report discusses an infant patient who presented with H-SS. Case presentation Through a multidisciplinary approach, this patient was also found to have very early onset inflammatory bowel disease (VEO-IBD) and Mevalonate kinase-associated disease (MKAD). While prior case studies have characterized an association between VEO-IBD and MKAD, there is no literature describing the association of all three diagnoses this case: H-SS, VEO-IBD and MKAD. Initiation of canakinumab in this patient resulted in successful control of the disease. Conclusions This case highlights the importance of a multidisciplinary approach to rare diagnoses, and collaboration during cases with significant diagnostic uncertainty.