Spontaneous Lesions of Endangered Geriatric Julia Creek Dunnarts (Sminthopsis douglasi, Archer 1979) with Emphasis in Reproductive Pathology.

Julia Creek dunnarts are an endangered species of carnivorous marsupials and the focus of multiple conservation strategies involving significant resources such as captive breeding programs. Despite the relevance for conservation, no study to date has focused on evaluating geriatric diseases in dunnarts. This study describes the pathology findings in a group of one wild and thirty-five captive-born, mostly geriatric Julia Creek dunnarts that failed to produce offspring over multiple breeding periods. A total of 20 females and 16 males were submitted for a postmortem examination, with ages ranging from 9 to 42 and 12 to 42 months for females and males, respectively. Of these, 10 had unremarkable findings. The most common condition in females was cystic glandular hyperplasia (n = 8), typical of hormonal dysregulation profiles in senescence, particularly hyperestrogenism. Rarely, cutaneous disease represented by unidentified dermal round cell infiltrates was observed in females (n = 2). Primary reproductive hormonal dysregulation was also suspected in males diagnosed with testicular degeneration, aspermatogenesis and/or atrophy (n = 3). Cutaneous round cell infiltrates, possibly compatible with epitheliotropic lymphomas, were seen in males (n = 3), and 2/3 affected males also had concurrent testicular degeneration or atrophy, indicating male sex could be a predictor for lymphoid neoplasia in aged dunnarts, especially in individuals with concurrent testosterone-luteinizing hormone dysregulation as it occurs in gonadectomized animals. The role of an underlying viral etiology is also explored. This study is the first to describe major spontaneous diseases in endangered aged Julia Creek dunnarts, providing an important understanding of senescence and geriatric diseases within a conservation context.

Developmental conversion of thymocyte-attracting cells into self-antigen-displaying cells in embryonic thymus medulla epithelium.

Thymus medulla epithelium establishes immune self-tolerance and comprises diverse cellular subsets. Functionally relevant medullary thymic epithelial cells (mTECs) include a self-antigen-displaying subset that exhibits genome-wide promiscuous gene expression promoted by the nuclear protein Aire and that resembles a mosaic of extrathymic cells including mucosal tuft cells. An additional mTEC subset produces the chemokine CCL21, thereby attracting positively selected thymocytes from the cortex to the medulla. Both self-antigen-displaying and thymocyte-attracting mTEC subsets are essential for self-tolerance. Here, we identify a developmental pathway by which mTECs gain their diversity in functionally distinct subsets. We show that CCL21-expressing mTECs arise early during thymus ontogeny in mice. Fate-mapping analysis reveals that self-antigen-displaying mTECs, including Aire-expressing mTECs and thymic tuft cells, are derived from CCL21-expressing cells. The differentiation capability of CCL21-expressing embryonic mTECs is verified in reaggregate thymus experiments. These results indicate that CCL21-expressing embryonic mTECs carry a developmental potential to give rise to self-antigen-displaying mTECs, revealing that the sequential conversion of thymocyte-attracting subset into self-antigen-displaying subset serves to assemble functional diversity in the thymus medulla epithelium.

Protocol for a parallel cluster randomized trial of a participatory tailored approach to reduce overuse of antibiotics at hospital discharge: the ROAD home trial.

BACKGROUND: Antibiotic overuse at hospital discharge is common, costly, and harmful. While discharge-specific antibiotic stewardship interventions are effective, they are resource-intensive and often infeasible for hospitals with resource constraints. This weakness impacts generalizability of stewardship interventions and has health equity implications as not all patients have access to the benefits of stewardship based on where they receive care. There may be different pathways to improve discharge antibiotic prescribing that vary widely in feasibility. Supporting hospitals in selecting interventions tailored to their context may be an effective approach to feasibly reduce antibiotic overuse at discharge across diverse hospitals. The objective of this study is to evaluate the effectiveness of the Reducing Overuse of Antibiotics at Discharge Home multicomponent implementation strategy ("ROAD Home") on antibiotic overuse at discharge for community-acquired pneumonia and urinary tract infection. METHODS: This 4-year two-arm parallel cluster-randomized trial will include three phases: baseline (23 months), intervention (12 months), and postintervention (12 months). Forty hospitals recruited from the Michigan Hospital Medicine Safety Consortium will undergo covariate-constrained randomization with half randomized to the ROAD Home implementation strategy and half to a "stewardship as usual" control. ROAD Home is informed by the integrated-Promoting Action on Research Implementation in Health Services Framework and includes (1) a baseline needs assessment to create a tailored suite of potential stewardship interventions, (2) supported decision-making in selecting interventions to implement, and (3) external facilitation following an implementation blueprint. The primary outcome is baseline-adjusted days of antibiotic overuse at discharge. Secondary outcomes include 30-day patient outcomes and antibiotic-associated adverse events. A mixed-methods concurrent process evaluation will identify contextual factors influencing the implementation of tailored interventions, and assess implementation outcomes including acceptability, feasibility, fidelity, and sustainment. DISCUSSION: Reducing antibiotic overuse at discharge across hospitals with varied resources requires tailoring of interventions. This trial will assess whether a multicomponent implementation strategy that supports hospitals in selecting evidence-based stewardship interventions tailored to local context leads to reduced overuse of antibiotics at discharge. Knowledge gained during this study could inform future efforts to implement stewardship in diverse hospitals and promote equity in access to the benefits of quality improvement initiatives. TRIAL REGISTRATION: Clinicaltrials.gov NCT06106204 on 10/30/23.

Development of patient safety measures to identify inappropriate diagnosis of common infections.

BACKGROUND: Inappropriate diagnosis of infections results in antibiotic overuse and may delay diagnosis of underlying conditions. Here, we describe the development and characteristics of two safety measures of inappropriate diagnosis of urinary tract infection (UTI) and community-acquired pneumonia (CAP), the most common inpatient infections on general medicine services. METHODS: Measures were developed from guidelines and literature and adapted based on data from patients hospitalized with UTI and CAP in 49 Michigan hospitals and feedback from end-users, a technical expert panel (TEP), and a patient focus group. Each measure was assessed for reliability, validity, feasibility, and usability. RESULTS: Two measures, now endorsed by the National Quality Forum (NQF), were developed. Measure reliability (derived from 24,483 patients) was excellent (0.90 for UTI; 0.91 for CAP). Both measures had strong validity demonstrated through a) face validity by hospital users, the TEPs, and patient focus group, b) implicit case review (ĸ 0.72 for UTI; ĸ 0.72 for CAP), and c) rare case misclassification (4% for UTI; 0% for CAP) due to data errors (<2% for UTI; 6.3% for CAP). Measure implementation through hospital peer comparison in Michigan hospitals (2017 to 2020) demonstrated significant decreases in inappropriate diagnosis of UTI and CAP (37% and 32%, respectively, p < 0.001), supporting usability. CONCLUSIONS: We developed highly reliable, valid, and usable measures of inappropriate diagnosis of UTI and CAP for hospitalized patients. Hospitals seeking to improve diagnostic safety, antibiotic use, and patient care should consider using these measures to reduce inappropriate diagnosis of CAP and UTI.

Assembling the thymus medulla: Development and function of epithelial cell heterogeneity.

The thymus is a unique primary lymphoid organ that supports the production of self-tolerant T-cells essential for adaptive immunity. Intrathymic microenvironments are microanatomically compartmentalised, forming defined cortical, and medullary regions each differentially supporting critical aspects of thymus-dependent T-cell maturation. Importantly, the specific functional properties of thymic cortical and medullary compartments are defined by highly specialised thymic epithelial cells (TEC). For example, in the medulla heterogenous medullary TEC (mTEC) contribute to the enforcement of central tolerance by supporting deletion of autoreactive T-cell clones, thereby counterbalancing the potential for random T-cell receptor generation to contribute to autoimmune disease. Recent advances have further shed light on the pathways and mechanisms that control heterogeneous mTEC development and how differential mTEC functionality contributes to control self-tolerant T-cell development. Here we discuss recent findings in relation to mTEC development and highlight examples of how mTEC diversity contribute to thymus medulla function.

Excellence in Antibiotic Stewardship: A mixed methods study comparing High, Medium, and Low Performing Hospitals.

BACKGROUND: Despite antibiotic stewardship programs existing in most acute care hospitals, there continues to be variation in appropriate antibiotic use. While existing research examines individual prescriber behavior, contextual reasons for variation are poorly understood. METHODS: We conducted an explanatory, sequential mixed methods study of a purposeful sample of 7 hospitals with varying discharge antibiotic overuse. For each hospital, we conducted surveys, document analysis, and semi-structured interviews with antibiotic stewardship and clinical stakeholders. Data were analyzed separately and mixed during the interpretation phase, where each hospital was examined as a case, with findings organized across cases using a strengths, weaknesses, opportunities, and threats framework to identify factors accounting for differences in antibiotic overuse across hospitals. RESULTS: Surveys included 85 respondents. Interviews included 90 respondents (31 hospitalists, 33 clinical pharmacists, 14 stewardship leaders, 12 hospital leaders). On surveys, clinical pharmacists at hospitals with lower antibiotic overuse were more likely to report feeling: respected by hospitalist colleagues (p=0.001), considered valuable team members (p=0.001), comfortable recommending antibiotic changes (p=0.02). Based on mixed-methods analysis, hospitals with low antibiotic overuse had four distinguishing characteristics: a) robust knowledge of and access to antibiotic stewardship guidance, b) high quality clinical pharmacist-physician relationships, c) tools and infrastructure to support stewardship, and d) highly engaged Infectious Diseases physicians who advocated stewardship principles. CONCLUSION: This mixed-method study demonstrates the importance of organizational context for high performance in stewardship and suggests improving antimicrobial stewardship requires attention to knowledge, interactions, and relationships between clinical teams and infrastructure that supports stewardship and team interactions.

The alarmin IL33 orchestrates type 2 immune-mediated control of thymus regeneration.

As the primary site of T-cell development, the thymus dictates immune competency of the host. The rates of thymus function are not constant, and thymus regeneration is essential to restore new T-cell production following tissue damage from environmental factors and therapeutic interventions. Here, we show the alarmin interleukin (IL) 33 is a product of Sca1+ thymic mesenchyme both necessary and sufficient for thymus regeneration via a type 2 innate immune network. IL33 stimulates expansion of IL5-producing type 2 innate lymphoid cells (ILC2), which triggers a cellular switch in the intrathymic availability of IL4. This enables eosinophil production of IL4 to re-establish thymic mesenchyme prior to recovery of thymopoiesis-inducing epithelial compartments. Collectively, we identify a positive feedback mechanism of type 2 innate immunity that regulates the recovery of thymus function following tissue injury.

Developmental conversion of thymocyte-attracting cells into self-antigen-displaying cells in embryonic thymus medulla epithelium.

Thymus medulla epithelium establishes immune self-tolerance and comprises diverse cellular subsets. Functionally relevant medullary thymic epithelial cells (mTECs) include a self-antigen-displaying subset that exhibits genome-wide promiscuous gene expression promoted by the nuclear protein Aire and that resembles a mosaic of extrathymic cells including mucosal tuft cells. An additional mTEC subset produces the chemokine CCL21, thereby attracting positively selected thymocytes from the cortex to the medulla. Both self-antigen-displaying and thymocyte-attracting mTEC subsets are essential for self-tolerance. Here we identify a developmental pathway by which mTECs gain their diversity in functionally distinct subsets. We show that CCL21-expressing mTECs arise early during thymus ontogeny. Fate-mapping analysis reveals that self-antigen-displaying mTECs, including Aire-expressing mTECs and thymic tuft cells, are derived from CCL21-expressing cells. The differentiation capability of CCL21-expressing embryonic mTECs is verified in reaggregate thymus experiments. These results indicate that CCL21-expressing embryonic mTECs carry a developmental potential to give rise to self-antigen-displaying mTECs, revealing that the sequential conversion of thymocyte-attracting subset into self-antigen-displaying subset serves to assemble functional diversity in the thymus medulla epithelium.

An exploratory cost-effectiveness analysis of a novel tissue valve compared with mechanical valves for surgical aortic valve replacement in subgroups of people aged 55-64 and 65+ with aortic stenosis in the UK.

OBJECTIVE: Exploratory analysis to conceptualize and evaluate the potential cost-effectiveness and economic drivers of using a novel tissue valve compared with mechanical heart valves for surgical aortic valve replacement (SAVR) in people aged 55-64 and 65+ with aortic stenosis (AS) from a National Health Service (NHS) UK perspective. METHODS: A decision-analytic model was developed using a partitioned survival model. Parameter inputs were obtained from published literature. Deterministic and probabilistic sensitivity analyses (DSA and PSA) were conducted to explore the uncertainty around the parameters. RESULTS: The novel tissue valve was potentially associated with higher quality-adjusted life years (QALYs) of 0.01 per person. Potential cost savings were greatest for those aged 55-64 (£408) versus those aged 65+(£53). DSA indicated the results to be most dependent on relative differences in general mortality, procedure costs, and reoperation rates. PSA estimated around 75% of the iterations to be cost-effective at £20,000 per QALY for those aged 55-64, and 57% for those aged 65+. CONCLUSIONS: The exploratory analysis suggests that the novel tissue valve could be a cost-effective intervention for people over the age of 55 with AS who are suitable for SAVR in the UK.

Budget impact analysis of a bovine pericardial aortic bioprosthesis versus mechanical aortic valve replacement in adult patients with aortic stenosis in Romania.

AIMS: An analysis of the budget impact of using a bovine pericardial aortic bioprosthesis (BPAB) or a mechanical valve (MV) in aortic stenosis (AS) patients in Romania. MATERIALS AND METHODS: A decision-tree with a partitioned survival model was used to predict the financial outcomes of using either a BPAB (the Carpentier-Edwards Perimount Magna Ease Valve) or MV in aortic valve replacement (AVR) procedure over a 5-year period. The budget impact of various resource consumption including disabling strokes, reoperations, minor thromboembolic events, major bleeding, endocarditis, anticoagulation treatment and monitoring, and echocardiogram assessments were compared for both types of valves. One-way sensitivity analyses (OWSA) were conducted on the input costs and probabilities. RESULTS: The use of BPAB compared to MV approaches budget neutrality due to incremental savings year-on-year. The initial surgical procedure and reoperation costs for BPAB are offset by savings in acenocoumarol use, disabling strokes, major bleeding, minor thromboembolic events, and anticoagulation complications. The cost of the initial procedure per patient is 460 euros higher for a BPAB due to the higher valve acquisition cost, although this is partially offset by a shorter hospital stay. The OWSA shows that the total procedure costs, including the hospital stay, are the primary cost drivers in the model. LIMITATIONS: Results are limited by cost data aggregation in the DRG system, exclusion of costs for consumables and capital equipment use, possible underestimation of outpatient complication costs, age-related variations of event rates, and valve durability. CONCLUSIONS: Adopting BPAB as a treatment option for AS patients in Romania can lead to cost savings and long-term economic benefits. By mitigating procedure costs and increasing anticoagulation treatment costs, BPAB offers a budget-neutral option that can help healthcare providers, policymakers, and patients alike manage the growing burden of AS in Romania.

Combined multidimensional single-cell protein and RNA profiling dissects the cellular and functional heterogeneity of thymic epithelial cells.

The network of thymic stromal cells provides essential niches with unique molecular cues controlling T cell development and selection. Recent single-cell RNA sequencing studies have uncovered previously unappreciated transcriptional heterogeneity among thymic epithelial cells (TEC). However, there are only very few cell markers that allow a comparable phenotypic identification of TEC. Here, using massively parallel flow cytometry and machine learning, we deconvoluted known TEC phenotypes into novel subpopulations. Using CITEseq, these phenotypes were related to corresponding TEC subtypes defined by the cells' RNA profiles. This approach allowed the phenotypic identification of perinatal cTEC and their physical localisation within the cortical stromal scaffold. In addition, we demonstrate the dynamic change in the frequency of perinatal cTEC in response to developing thymocytes and reveal their exceptional efficiency in positive selection. Collectively, our study identifies markers that allow for an unprecedented dissection of the thymus stromal complexity, as well as physical isolation of TEC populations and assignment of specific functions to individual TEC subtypes.

COVID-19-Related Publications by Hospitalists in the United States.

Objective To determine the degree to which hospitalists published academic manuscripts related to COVID-19 during the first year of the pandemic. Patients and methods The study was a cross-sectional analysis of the author's specialty, defined by byline or professional online biography, from articles related to COVID-19 published between March 1, 2020, and February 28, 2021. It included the top four internal medicine journals by impact factor: New England Journal of Medicine, Journal of the American Medical Association, Journal of the American Medical Association Internal Medicine, and Annals of Internal Medicine. Participants were all United States (US)-based physician authors contributing to COVID-19 publications. Our primary outcome was the percentage of US-based physician authors of COVID-19 articles who were hospitalists. Subgroup analyses characterized author specialty by authorship position (first, middle, last) and article type (research vs. non-research). Results Between March 1, 2020, and February 28, 2021, the top four US-based medical journals published 870 articles related to COVID-19 of which 712 articles with 1940 US-based physician authors were included. Hospitalists accounted for 4.2% (82) of authorship positions including 4.7% (49/1038) of authorship positions in research articles and 3.7% (33/902) of authorship positions in non-research articles. First, middle, and last authorship positions were held by hospitalists at 3.7% (18/485), 4.4% (45/1034), and 4.5% (19/421) of the time, respectively. Conclusions Despite caring for a large number of patients with COVID-19, hospitalists were rarely involved in disseminating COVID-19 knowledge. Limited authorship by hospitalists could constrain the dissemination of inpatient medicine knowledge, impact patient outcomes, and affect the academic promotion of early-career hospitalists.

Embryonic keratin19+ progenitors generate multiple functionally distinct progeny to maintain epithelial diversity in the adult thymus medulla.

The thymus medulla is a key site for immunoregulation and tolerance, and its functional specialisation is achieved through the complexity of medullary thymic epithelial cells (mTEC). While the importance of the medulla for thymus function is clear, the production and maintenance of mTEC diversity remains poorly understood. Here, using ontogenetic and inducible fate-mapping approaches, we identify mTEC-restricted progenitors as a cytokeratin19+ (K19+) TEC subset that emerges in the embryonic thymus. Importantly, labelling of a single cohort of K19+ TEC during embryogenesis sustains the production of multiple mTEC subsets into adulthood, including CCL21+ mTEClo, Aire+ mTEChi and thymic tuft cells. We show K19+ progenitors arise prior to the acquisition of multiple mTEC-defining features including RANK and CCL21 and are generated independently of the key mTEC regulator, Relb. In conclusion, we identify and define a multipotent mTEC progenitor that emerges during embryogenesis to support mTEC diversity into adult life.

The medulla controls effector primed γδT-cell development in the adult mouse thymus.

γδT cells are produced in the thymus throughout life and provide immunity at epithelial-rich sites. Unlike conventional αßT cells, γδT-cell development involves intrathymic acquisition of effector function, with priming for either IL17 or IFN-γ production occurring during embryonic or adult life, respectively. How the thymus controls effector-primed γδT-cell generation in adulthood is poorly understood. Here, we distinguished de novo γδT cells from those undergoing thymus recirculation and/or retention using Rag2GFP mice alongside markers of maturation/effector priming including CD24, CD25, CD73, and IFN-γ, the latter by crossing with IFN-γYFP GREAT mice. We categorize newly developing γδT-cells into an ordered sequence where CD25+ CD73- IFN-γYFP- precursors are followed sequentially by CD25- CD73+ IFN-γYFP- intermediates and CD25- CD73+ IFN-γYFP+ effectors. To determine intrathymic requirements controlling this sequence, we examined γδT-cell development in Relb-/- thymus grafts that lack medullary microenvironments. Interestingly, medulla deficiency did not alter CD25+ γδT-cell precursor generation, but significantly impaired development of effector primed stages. This impact on γδT-cell priming was mirrored in plt/plt mice lacking the medullary chemoattractants CCL19 and CCL21, and also Ccl21a-/- but not Ccl19-/- mice. Collectively, we identify the medulla as an important site for effector priming during adult γδT-cell development and demonstrate a specific role for the medullary epithelial product CCL21 in this process.

Frontofacial Surgery: Reducing Infection with the Development and 6-Year Outcome of a Frontofacial Protocol.

BACKGROUND: Frontofacial surgery (FFS) creates a communication between the cranial and nasal cavities and is associated with significant infection risk. After a cluster of infections affecting patients undergoing FFS, a root cause analysis of index cases was undertaken, but no specifically remedial causes were identified. Basic principles incorporating known risk factors for the prevention of surgical-site infection were then applied to the creation of a perioperative management protocol. This study analyzes infection rates before and after its implementation. METHODS: The protocol was designed around the needs of patients undergoing FFS and consists of three checklists covering their preoperative, intraoperative, and postoperative care. Compliance required the completion of each checklist. All patients undergoing FFS between 1999 and 2019 were studied retrospectively, and infections occurring before and after the implementation of the protocol were analyzed. RESULTS: One hundred three patients underwent FFS (60 monobloc and 36 facial bipartition) before the implementation of the protocol in August of 2013, and 30 patients underwent FFS after its implementation. Compliance with the protocol was 95%. After implementation, there was a statistically significant reduction in infections from 41.7% to 13.3% ( P = 0.005). CONCLUSIONS: Although no specific cause for a cluster of postoperative infection had been identified, the implementation of a bespoke protocol consisting of preoperative, perioperative, and postoperative checklists covering measures known to reduce infection risk was associated with a significant reduction in postoperative infections in patients undergoing FFS. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Gender differences in COVID-19-related manuscript authorship by hospitalists during the pandemic: A bibliometric analysis.

BACKGROUND: Hospital medicine (HM) has a well-described gender disparity related to academic work and promotion. During the COVID-19 pandemic, female authorship across medicine fell further behind historical averages. OBJECTIVE: Examine how COVID-19 affected the publication gender gap for hospitalists. DESIGN, SETTINGS, AND PARTICIPANTS: Bibliometric analysis to determine gender and specialty of US-based physician first and last authors of COVID-19 articles published March 1, 2020 to February 28, 2021 in the four highest impact general medical journals and two highest impact HM-specific journals. MAIN OUTCOME AND MEASURES: We characterized the percentage of all physician authors that were women, the percentage of physician authors that were hospitalists, and the percentage of HM authors that were women. We compared author gender between general medical and HM-specific journals. RESULTS: During the study period, 853 manuscripts with US-based first or last authors were published in eligible journals. Included manuscripts contained 1124 US-based physician first or last author credits, of which 34.2% (384) were women and 8.8% (99) were hospitalists. Among hospitalist author credits, 43.4% (n = 43/99) were occupied by women. The relative gender equity for hospitalist authors was driven by the two HM journals where, compared to the four general medical journals, hospitalist authors (54.1% [33/61] vs. 26.3% [10/38] women, respectively, p = .002) and hospitalist last authors (51.9% [14/27] vs. 20% [4/20], p = .03) were more likely to be women. CONCLUSIONS: Across COVID-19-related manuscripts, disparities by gender were driven by the high-impact general medical journals. HM-specific journals had more equitable inclusion of women authors, demonstrating the potential impact of proactive editorial policies on diversity.

Diversity in Cortical Thymic Epithelial Cells Occurs through Loss of a Foxn1-Dependent Gene Signature Driven by Stage-Specific Thymocyte Cross-Talk.

In the thymus, cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells support αßT cell development from lymphoid progenitors. For cTECs, expression of a specialized gene signature that includes Cxcl12, Dll4, and Psmb11 enables the cortex to support T lineage commitment and the generation and selection of CD4+CD8+ thymocytes. Although the importance of cTECs in T cell development is well defined, mechanisms that shape the cTEC compartment and regulate its functional specialization are unclear. Using a Cxcl12DsRed reporter mouse model, we show that changes in Cxcl12 expression reveal a developmentally regulated program of cTEC heterogeneity. Although cTECs are uniformly Cxcl12DsRed+ during neonatal stages, progression through postnatal life triggers the appearance of Cxcl12DsRed- cTECs that continue to reside in the cortex alongside their Cxcl12DsRed+ counterparts. This appearance of Cxcl12DsRed- cTECs is controlled by maturation of CD4-CD8-, but not CD4+CD8+, thymocytes, demonstrating that stage-specific thymocyte cross-talk controls cTEC heterogeneity. Importantly, although fate-mapping experiments show both Cxcl12DsRed+ and Cxcl12DsRed- cTECs share a common Foxn1+ cell origin, RNA sequencing analysis shows Cxcl12DsRed- cTECs no longer express Foxn1, which results in loss of the FOXN1-dependent cTEC gene signature and may explain the reduced capacity of Cxcl12DsRed- cTECs for thymocyte interactions. In summary, our study shows that shaping of the cTEC compartment during the life course occurs via stage-specific thymocyte cross-talk, which drives loss of Foxn1 expression and its key target genes, which may then determine the functional competence of the thymic cortex.

Diversity in Cortical Thymic Epithelial Cells Occurs through Loss of a Foxn1-Dependent Gene Signature Driven by Stage-Specific Thymocyte Cross-Talk.

In the thymus, cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells support αßT cell development from lymphoid progenitors. For cTECs, expression of a specialized gene signature that includes Cxcl12, Dll4, and Psmb11 enables the cortex to support T lineage commitment and the generation and selection of CD4+CD8+ thymocytes. Although the importance of cTECs in T cell development is well defined, mechanisms that shape the cTEC compartment and regulate its functional specialization are unclear. Using a Cxcl12 DsRed reporter mouse model, we show that changes in Cxcl12 expression reveal a developmentally regulated program of cTEC heterogeneity. Although cTECs are uniformly Cxcl12 DsRed+ during neonatal stages, progression through postnatal life triggers the appearance of Cxcl12 DsRed- cTECs that continue to reside in the cortex alongside their Cxcl12 DsRed+ counterparts. This appearance of Cxcl12 DsRed- cTECs is controlled by maturation of CD4-CD8-, but not CD4+CD8+, thymocytes, demonstrating that stage-specific thymocyte cross-talk controls cTEC heterogeneity. Importantly, although fate-mapping experiments show both Cxcl12 DsRed+ and Cxcl12 DsRed- cTECs share a common Foxn1 + cell origin, RNA sequencing analysis shows Cxcl12 DsRed- cTECs no longer express Foxn1, which results in loss of the FOXN1-dependent cTEC gene signature and may explain the reduced capacity of Cxcl12 DsRed- cTECs for thymocyte interactions. In summary, our study shows that shaping of the cTEC compartment during the life course occurs via stage-specific thymocyte cross-talk, which drives loss of Foxn1 expression and its key target genes, which may then determine the functional competence of the thymic cortex.

Eosinophils are an essential element of a type 2 immune axis that controls thymus regeneration.

Therapeutic interventions used for cancer treatment provoke thymus damage and limit the recovery of protective immunity. Here, we show that eosinophils are an essential part of an intrathymic type 2 immune network that enables thymus recovery after ablative therapy. Within hours of damage, the thymus undergoes CCR3-dependent colonization by peripheral eosinophils, which reestablishes the epithelial microenvironments that control thymopoiesis. Eosinophil regulation of thymus regeneration occurs via the concerted action of NKT cells that trigger CCL11 production via IL4 receptor signaling in thymic stroma, and ILC2 that represent an intrathymic source of IL5, a cytokine that therapeutically boosts thymus regeneration after damage. Collectively, our findings identify an intrathymic network composed of multiple innate immune cells that restores thymus function during reestablishment of the adaptive immune system.