Thymic regulatory T cells arise via two distinct developmental programs.

The developmental programs that generate a broad repertoire of regulatory T cells (Treg cells) able to respond to both self antigens and non-self antigens remain unclear. Here we found that mature Treg cells were generated through two distinct developmental programs involving CD25+ Treg cell progenitors (CD25+ TregP cells) and Foxp3lo Treg cell progenitors (Foxp3lo TregP cells). CD25+ TregP cells showed higher rates of apoptosis and interacted with thymic self antigens with higher affinity than did Foxp3lo TregP cells, and had a T cell antigen receptor repertoire and transcriptome distinct from that of Foxp3lo TregP cells. The development of both CD25+ TregP cells and Foxp3lo TregP cells was controlled by distinct signaling pathways and enhancers. Transcriptomics and histocytometric data suggested that CD25+ TregP cells and Foxp3lo TregP cells arose by coopting negative-selection programs and positive-selection programs, respectively. Treg cells derived from CD25+ TregP cells, but not those derived from Foxp3lo TregP cells, prevented experimental autoimmune encephalitis. Our findings indicate that Treg cells arise through two distinct developmental programs that are both required for a comprehensive Treg cell repertoire capable of establishing immunotolerance.

Costimulation via the tumor-necrosis factor receptor superfamily couples TCR signal strength to the thymic differentiation of regulatory T cells.

Regulatory T cells (Treg cells) express members of the tumor-necrosis factor (TNF) receptor superfamily (TNFRSF), but the role of those receptors in the thymic development of Treg cells is undefined. We found here that Treg cell progenitors had high expression of the TNFRSF members GITR, OX40 and TNFR2. Expression of those receptors correlated directly with the signal strength of the T cell antigen receptor (TCR) and required the coreceptor CD28 and the kinase TAK1. The neutralization of ligands that are members of the TNF superfamily (TNFSF) diminished the development of Treg cells. Conversely, TNFRSF agonists enhanced the differentiation of Treg cell progenitors by augmenting responsiveness of the interleukin 2 receptor (IL-2R) and transcription factor STAT5. Costimulation with the ligand of GITR elicited dose-dependent enrichment for cells of lower TCR affinity in the Treg cell repertoire. In vivo, combined inhibition of GITR, OX40 and TNFR2 abrogated the development of Treg cells. Thus, expression of members of the TNFRSF on Treg cell progenitors translated strong TCR signals into molecular parameters that specifically promoted the development of Treg cells and shaped the Treg cell repertoire.

Prolonged Elevations of Factor VIII and von Willebrand Factor Antigen After Multisystem Inflammatory Syndrome in Children.

Multisystem Inflammatory Syndrome in Children (MIS-C) is a late systemic inflammatory response to a recent mild or asymptomatic coronavirus disease of 2019 infection. The pathophysiology is incompletely understood but it often features significant coagulopathy along with cardiac and endothelial dysfunction. Endothelial inflammation has been primarily described in acute coronavirus disease of 2019 infection, with less characterization in MIS-C. Here we describe novel findings of nearly universal severe and prolonged factor VIII (FVIII) and von Willebrand factor antigen elevations in an institutional cohort of patients with MIS-C ages younger than or 21 years old (N=31). All patients had elevated acute phase reactants and D-dimer at presentation and met published criteria for MIS-C. FVIII was high at presentation in 97% of patients but continued to rise during the ensuing weeks of treatment to a mean 429%, peaking on median day 17 of illness as an outpatient. FVIII levels were >600% in multiple patients. von Willebrand factor antigen was measured less frequently but showed similar trends. These escalations occurred amidst resolving cardiac dysfunction and acute phase reactant normalization and despite patients receiving multimodal anti-inflammatory treatments and aspirin and enoxaparin thromboprophylaxis. No thrombotic events occurred. Endothelial dysfunction represented by very elevated FVIII levels may persist longer than other acute phase reactants may reflect.

Identification of Cellular Sources of IL-2 Needed for Regulatory T Cell Development and Homeostasis.

The cytokine IL-2 is critical for promoting the development, homeostasis, and function of regulatory T (Treg) cells. The cellular sources of IL-2 that promote these processes remain unclear. T cells, B cells, and dendritic cells (DCs) are known to make IL-2 in peripheral tissues. We found that T cells and DCs in the thymus also make IL-2. To identify cellular sources of IL-2 in Treg cell development and homeostasis, we used Il2FL/FL mice to selectively delete Il2 in T cells, B cells, and DCs. Because IL-15 can partially substitute for IL-2 in Treg cell development, we carried out the majority of these studies on an Il15-/- background. Deletion of Il2 in B cells, DCs, or both these subsets had no effect on Treg cell development, either in wild-type (WT) or Il15-/- mice. Deletion of Il2 in T cells had minimal effects in WT mice but virtually eliminated developing Treg cells in Il15-/- mice. In the spleen and most peripheral lymphoid organs, deletion of Il2 in B cells, DCs, or both subsets had no effect on Treg cell homeostasis. In contrast, deletion of Il2 in T cells led to a significant decrease in Treg cells in either WT or Il15-/- mice. The one exception was the mesenteric lymph nodes where significantly fewer Treg cells were observed when Il2 was deleted in both T cells and DCs. Thus, T cells are the sole source of IL-2 needed for Treg cell development, but DCs can contribute to Treg cell homeostasis in select organs.

The CD4+ T cell repertoire specific for citrullinated peptides shows evidence of immune tolerance.

Rheumatoid arthritis occurs most often in people who express HLA-DR molecules containing a five aa "shared epitope" in the ß chain. These MHCII molecules preferentially bind citrullinated peptides formed by posttranslational modification of arginine. Citrullinated peptide:HLA-DR complexes may act as arthritis-initiating neo-antigens for CD4+ T cells. Here, we used fluorophore-conjugated HLA-DR tetramers containing citrullinated peptides from human cartilage intermediate layer protein, fibrinogen, vimentin, or enolase 1 to track cognate CD4+ T cells. Immunization of HLA-DR transgenic mice with citrullinated peptides from vimentin or enolase 1 failed to cause any expansion of tetramer-binding cells, whereas immunization with citrullinated peptides from cartilage intermediate layer protein or fibrinogen elicited some expansion. The expanded tetramer-binding populations, however, had lower T helper 1 and higher regulatory T cell frequencies than populations elicited by viral peptides. These results indicate that HLA-DR-bound citrullinated peptides are not neo-antigens and induce varying degrees of immune tolerance that could pose a barrier to rheumatoid arthritis.

HLA-DRB1*15 and Eosinophilia Are Common Among Patients With Systemic Juvenile Idiopathic Arthritis.

OBJECTIVE: Concern exists that medications used to treat patients with systemic juvenile idiopathic arthritis (JIA), particularly interleukin (IL)-1 and IL-6 blocking agents, might be causing adverse drug reactions and lung disease (systemic JIA-LD). Carriage of HLA-DRB1*15 has been reported as a risk factor for adverse drug reactions among patients with systemic JIA. We performed a retrospective chart review to evaluate these factors at our center. METHODS: We reviewed the records of 86 subjects with systemic JIA followed for at least 6 months between 1996 and 2022. HLA typing was performed in 23 of the subjects. We compared characteristics of patients with or without eosinophilia. Among patients with HLA typing, we compared clinical characteristics of subjects with or without DRB1*15 and with or without systemic JIA-LD. RESULTS: Among the 23 patients with HLA typing, 74% carried DRB1*15, and 63% of patients without systemic JIA-LD carried DRB1*15. Seven subjects had systemic JIA-LD, all of whom carried DRB1*15. Patients with systemic JIA-LD were younger at the time of diagnosis and more likely to have had macrophage activation syndrome. Exposure to IL-1 and IL-6 blockers was common, occurring in 95% of patients. Eosinophilia occurred in 39% of patients with systemic JIA, often before IL-1 or IL-6 blockade. Eosinophilia was associated with adverse drug reactions and macrophage activation syndrome. There was 1 death, unrelated to active systemic JIA disease. CONCLUSION: Carriage of DRB1*15 was more common in this cohort of patients with systemic JIA than in the general population. Eosinophilia and systemic JIA-LD were more common among patients with severe systemic JIA complicated by macrophage activation syndrome.

Non-criteria antiphospholipid antibodies and pediatric rheumatic disease: a case series.

BACKGROUND: Non-criteria antiphospholipid antibodies (NC-aPL) are a relatively undefined subgroup of antiphospholipid antibodies (aPL). Knowledge about NC-aPL in adults is limited and even less is known in pediatric patients. Routine tests for antiphospholipid syndrome (APS)-a clinical state marked by the presence of aPL in association with vascular thrombosis-usually include lupus anticoagulant (LAC), anti-cardiolipin (aCL) and -beta-2 glycoprotein I (aß2GPI). LAC is a functional screen for prothrombotic aPL, while the latter tests identify specific autoantibodies. Specific targets of NC-aPL include, but are not limited to, phosphatidylethanolamine, phosphatidylserine, and prothrombin. PRESENTATION OF CASES: We present single-center data from eight pediatric patients with NC-aPL identified during a three-year period. All patients had presenting features raising suspicion for APS. Most patients were female with a primary rheumatic disease. One patient had a stroke. Another patient had alveolar hemorrhage and pulmonary hypertension. Raynaud's phenomenon, rashes involving distal extremities, and headaches were common. Most patients had a positive LAC, yet their routine aPL tests were negative, prompting testing for NC-aPL. CONCLUSIONS: Our findings suggest NC-aPL are associated with typical signs and symptoms of APS in pediatric patients. Pediatricians and pediatric subspecialists should consider NC-aPL when clinical suspicion is high and routine aPL tests are negative, particularly when LAC is positive. While guidelines for NC-aPL do not yet exist for children or adults, these autoantibodies have pathogenic potential. Actionable items could include evaluation for the presence of other (primary) rheumatic diseases, and consultation with hematologists and/or obstetricians regarding anticoagulation/platelet inhibition and thrombosis education. Future guidelines regarding NC-aPL will only be generated by gathering more data, ideally prospectively.

Capturing critical data elements in Juvenile Idiopathic Arthritis: initiatives to improve data capture.

BACKGROUND: Documentation of critical data elements is a focus of the Pediatric Rheumatology Care and Outcomes Improvement Network to aid in clinical care and research for patients with juvenile idiopathic arthritis. We aimed to increase data capture for critical data elements and hypothesized that quality improvement methodology would improve data capture. We also hypothesized that data capture for all critical data elements would be lower for virtual visits compared to in-person visits. METHODS: All visits for patients with JIA between 9/14/2020 and 12/31/2021 at the University of Minnesota were included. We assessed completeness of critical data element capture. Sixteen interventions with providers were conducted, including email reminders, individual discussions, group meetings, and feedback reports. We used statistical process control charts to evaluate change over time. RESULTS: Baseline included 355 patient-visits: 221 (62%) in-person and 134 (38%) virtual with critical data elements entry ranging between 50 and 60%. Post-intervention included 1,596 patient-visits: 1,350 (85%) in-person and 246 (15%) virtual, with critical data elements entry reaching 91%. All providers improved data entry during this study. In-person visits had significantly higher data capture rates than virtual visits for all 4 critical data elements. CONCLUSION: We achieved our aim to increase critical data element documentation by focusing on provider buy-in, frequent reminders, and individualized feedback. We also found that collection of critical data elements occurred significantly less often with virtual visits than with in-person visits. Now that we improved capture of critical data elements, we can shift the focus to efforts aimed at improving outcomes for patients with juvenile arthritis.

Using quality improvement methodology and tools to reduce patient wait time in a paediatric subspecialty rheumatology clinic.

Our paediatric rheumatology clinic has experienced inefficient patient flow. Our aim was to reduce mean wait time and minimise variation for patients. Baseline data showed that most waiting occurs after a patient has been roomed, while waiting for the physician. Wait time was not associated with a patient's age, time of day, day of the week or individual physician. We implemented a checkout sheet and staggered start times. After a series of plan-do-study-act cycles, we observed an initial 26% reduction in the variation of wait time and a final 17% reduction in the mean wait time. There was no impact on patient-physician contact time. Overall, we demonstrate how process improvement methodology and tools were used to reduce patient wait time in our clinic, adding to the body of literature on process improvement in an ambulatory setting.

IL-2, -7, and -15, but not thymic stromal lymphopoeitin, redundantly govern CD4+Foxp3+ regulatory T cell development.

Common gamma chain (gammac)-receptor dependent cytokines are required for regulatory T cell (Treg) development as gammac(-/-) mice lack Tregs. However, it is unclear which gammac-dependent cytokines are involved in this process. Furthermore, thymic stromal lymphopoietin (TSLP) has also been suggested to play a role in Treg development. In this study, we demonstrate that developing CD4(+)Foxp3(+) Tregs in the thymus express the IL-2Rbeta, IL-4Ralpha, IL-7Ralpha, IL-15Ralpha, and IL-21Ralpha chains, but not the IL9Ralpha or TSLPRalpha chains. Moreover, only IL-2, and to a much lesser degree IL-7 and IL-15, were capable of transducing signals in CD4(+)Foxp3(+) Tregs as determined by monitoring STAT5 phosphorylation. Likewise, IL-2, IL-7, and IL-15, but not TSLP, were capable of inducing the conversion of CD4(+)CD25(+)Foxp3(-) thymic Treg progenitors into CD4(+)Foxp3(+) mature Tregs in vitro. To examine this issue in more detail, we generated IL-2Rbeta(-/-) x IL-7Ralpha(-/-) and IL-2Rbeta(-/-) x IL-4Ralpha(-/-) mice. We found that IL-2Rbeta(-/-) x IL-7Ralpha(-/-) mice were devoid of Tregs thereby recapitulating the phenotype observed in gammac(-/-) mice; in contrast, the phenotype observed in IL-2Rbeta(-/-) x IL-4Ralpha(-/-) mice was comparable to that seen in IL-2Rbeta(-/-) mice. Finally, we observed that Tregs from both IL-2(-/-) and IL-2Rbeta(-/-) mice show elevated expression of IL-7Ralpha and IL-15Ralpha chains. Addition of IL-2 to Tregs from IL-2(-/-) mice led to rapid down-regulation of these receptors. Taken together, our results demonstrate that IL-2 plays the predominant role in Treg development, but that in its absence the IL-7Ralpha and IL-15Ralpha chains are up-regulated and allow for IL-7 and IL-15 to partially compensate for loss of IL-2.

On the Alert for Cytokine Storm: Immunopathology in COVID-19.

Poor outcomes in COVID-19 correlate with clinical and laboratory features of cytokine storm syndrome. Broad screening for cytokine storm and early, targeted antiinflammatory therapy may prevent immunopathology and could help conserve limited health care resources. While studies are ongoing, extrapolating from clinical experience in cytokine storm syndromes may benefit the multidisciplinary teams caring for patients with severe COVID-19.

Autoantibodies in the Pathogenesis, Diagnosis, and Prognosis of Juvenile Idiopathic Arthritis.

Autoantibody production occurs in juvenile idiopathic arthritis (JIA) and numerous other autoimmune diseases. In some conditions, the autoantibodies are clearly pathogenic, whereas in others the roles are less defined. Here we review various autoantibodies associated with JIA, with a particular focus on antinuclear antibodies and antibodies recognizing citrullinated self-antigens. We explore potential mechanisms that lead to the development of autoantibodies and the use of autoantibody testing in diagnosis and prognosis. Finally, we compare and contrast JIA-associated autoantibodies with those found in adults with rheumatoid arthritis (RA).

Interleukin-2 and STAT5 in regulatory T cell development and function.

Interleukin-2 and its downstream target STAT5 have effects on many aspects of immune function. This has been perhaps best documented in regulatory T cells. In this review we summarize the initial findings supporting a role for IL2 and STAT5 in regulatory T cell development and outline more recent studies describing how this critical signaling pathway entrains regulatory T cell differentiation and affects regulatory T cell function.

Endogenous platelet factor 4 stimulates activated protein C generation in vivo and improves survival after thrombin or lipopolysaccharide challenge.

Pharmacologic infusion of activated protein C (APC) improves survival in severe sepsis, and platelet factor 4 (PF4) accelerates APC generation in a primate thrombin-infusion model. We now tested whether endogenous platelet PF4 content affects APC generation. Mice completely deficient in PF4 (mPF4(-/-)) had impaired APC generation and survival after thrombin infusion, similar to the impairment seen in heterozygote protein C-deficient (PC(+/-)) mice. Transgenic mice overexpressing human PF4 (hPF4(+)) had increased plasma APC generation. Overexpression of platelet PF4 compensated for the defect seen in PC(+/-) mice. In both a thrombin and a lipopolysaccharide (LPS) survival model, hPF4(+) and PC(+/-)/hPF4(+) mice had improved survival. Further, infusion of hPF4(+) platelets improved survival of wild-type mice after an LPS challenge. These studies suggest that endogenous PF4 release may have biologic consequences for APC generation and survival in clinical sepsis. Infusions of PF4-rich platelets may be an effective strategy to improve outcome in this setting.

Histone deacetylase inhibitors suppress TF-kappaB-dependent agonist-driven tissue factor expression in endothelial cells and monocytes.

Histone deacetylase inhibitors (HDACi), such as trichostatin A (TSA), can regulate gene expression by promoting acetylation of histones and transcription factors. Human tissue factor (TF) expression is partly governed by a unique, NF-kappaB-related "TF-kappaB" promoter binding site. We find that TSA and four other HDACi (apicidin, MS-275, sodium butyrate, and valproic acid) all inhibit by approximately 90% TF activity and protein level induction in human umbilical vein endothelial cells stimulated by the physiologic agonists tumor necrosis factor (TNF)-alpha, interleukin-1beta, lipopolysaccharide, and HOSCN without affecting expression of the NF-kappaB-regulated adhesion molecules ICAM-1 and E-selectin. TSA and butyrate also blunt TF induction approximately 50% in vitro in peripheral blood mononuclear cells and in vivo in thioglycolate-elicited murine peritoneal macrophages. In human umbilical vein endothelial cells, TSA attenuates by approximately 70% TNF-alpha stimulation of TF mRNA transcription without affecting that of ICAM-1. By electrophoretic mobility shift assay analyses, TNF-alpha and lipopolysaccharide induce strong p65/p50 and p65/c-Rel heterodimer binding to both NF-kappaB and TF-kappaB probes. TSA nearly abolishes TF-kappaB binding without affecting NF-kappaB binding. A chromatin immunoprecipitation assay and a promoter-luciferase reporter system confirm that TSA inhibits TF-kappaB but not NF-kappaB activation. Chromatin immunoprecipitation and small interfering RNA inhibitor studies demonstrate that HDAC3 plays a significant role in TNF-alpha-mediated TF induction. Thus, HDACi transcriptionally inhibit agonist-induced TF expression in endothelial cells and monocytes by a TF-kappaB- and HDAC3-dependent mechanism. We conclude that histone deacetylases, particularly HDAC3, play a hitherto unsuspected role in regulating TF expression and raise the possibility that HDACi might be a novel therapy for thrombotic disorders.

Thiocyanate-dependent induction of endothelial cell adhesion molecule expression by phagocyte peroxidases: a novel HOSCN-specific oxidant mechanism to amplify inflammation.

Both eosinophil peroxidase (EPO) and neutrophil myeloperoxidase (MPO) preferentially oxidize SCN(-) to generate HOSCN, a weak, sulfhydryl-reactive oxidant, as a major physiologic product. We here show that HOSCN is a uniquely potent phagocyte oxidant inducer of E-selectin, ICAM-1, and VCAM-1 expression in HUVEC as detected by Western blot and flow cytometry. EMSA and inhibitor studies show that HOSCN up-regulation of these adhesion molecules is transcriptionally mediated through a mechanism that is dependent upon activation of the NF-kappaB p65/p50 transcription factor and constitutively suppressed by PI3K-Akt pathway activity. HUVEC monolayers exposed to HOSCN bind 8-fold more neutrophils and 3- to 4-fold more Aml14.3D10 cells (a differentiated cell line model of mature eosinophils) than control monolayers. Blocking Ab studies confirm the involvement of E-selectin and ICAM-1 but not VCAM-1 in neutrophil adhesion and of all three in Aml14.3D10 adhesion. Intraperitoneal injection of HOSCN evoked an 8-fold increase in neutrophil peritoneal extravasation. In addition to NF-kappaB, HOSCN also activates the potentially proinflammatory transcription factors Stat4, CDP, GRE, CBF, Ets-1/PEA3, and TFIID, a pattern easily distinguishable from that induced by LPS. These results suggest that phagocyte peroxidases function to amplify inflammation through a novel, HOSCN-specific oxidant mechanism.

The principal eosinophil peroxidase product, HOSCN, is a uniquely potent phagocyte oxidant inducer of endothelial cell tissue factor activity: a potential mechanism for thrombosis in eosinophilic inflammatory states.

In vivo, bromide (Br(-)), nitrite (NO(2)(-)), and thiocyanate (SCN(-)) compete for oxidation by eosinophil peroxidase (EPO) and H(2)O(2), yielding, respectively, HOBr, NO(2)., and HOSCN. We have recently shown that SCN(-) is the strongly preferred substrate for EPO in vivo and that HOSCN, in contrast with other EPO-generated oxidants and HOCl, is a relatively weak, cell-permeant, sulfhydryl (SH)-reactive oxidant. We here show that HOSCN is a uniquely potent (up to 100-fold) phagocyte oxidant inducer of tissue factor (TF) activity in human umbilical vein endothelial cells (HUVECs). This induction is attributable to transcriptional up-regulation of TF gene expression dependent upon both activation of the p65/c-Rel TF-kappaB transcription factor and activity of the ERK1/2 kinase pathway upstream of Egr-1 and was markedly further enhanced in the presence of wortmannin, an inhibitor of the PI3 kinase/Akt pathway. HOSCN also markedly activates the proinflammatory p65/p50 NF-kappaB pathway. Based on these findings we hypothesize that HOSCN generated by adherent and infiltrating eosinophils may provoke the development of a prothrombotic and proinflammatory endothelial/endocardial phenotype that promotes the pronounced thrombotic diathesis characteristic of the hypereosinophilic syndrome.