and ovalbumin-challenged mice. See the publication by Abdala-Valencia et al. 1 for a detailed description of the ovalbumin model of asthma and eosinophil sorting protocol.

CAPSULE SUMMARY We show that Tenascin-C, an asthma-associated extracellular matrix glycoprotein, promotes hematopoietic progenitors and suppresses the IL-5-driven maturation of murine lung eosinophils. The extracellular matrix’s regulation of in situ hematopoiesis has significant implications for targeting tissue eosinophils.

Bone marrow is a hematopoietic site harboring multiple populations of myeloid cells in different stages of differentiation. Murine bone marrow eosinophils are traditionally identified by Siglec‐F(+) staining using flow cytometry, whereas neutrophils are characterized by Ly6G(+) expression. However, using flow cytometry to characterize bone marrow hematopoietic cells in wild‐type mice, we found substantial gray areas in identification of these cells. Siglec‐F(+) mature eosinophil population constituted only a minority of bone marrow Lin(+)CD45(+) pool (5%). A substantial population of Siglec‐F(−) cells was double positive for neutrophil marker Ly6G and eosinophil lineage marker, IL‐5Rα. This granulocyte population with mixed neutrophil and eosinophil characteristics is typically attributable to neutrophil pool based on neutral granule staining and expression of Ly6G and myeloid peroxidase. It is distinct from Lineage(−) myeloid progenitors or Siglec‐F(+)Ly6G(+) maturing eosinophil precursors, and can be accurately identified by Lineage(+) staining and positive expression of markers IL‐5Rα and Ly6G. At 15–50% of all CD45(+) hematopoietic cells in adult mice (percentage varies by sex and age), this is a surprisingly dominant population, which increases with age in both male and female mice. RNA‐seq characterization of these cells revealed a complex immune profile and the capacity to secrete constituents of the extracellular matrix. When sorted from bone marrow, these resident cells had neutrophilic phenotype but readily acquired all characteristics of eosinophils when cultured with G‐CSF or IL‐5, including expression of Siglec‐F and granular proteins (Epx, Mbp). Surprisingly, these cells were also able to differentiate into Ly6C(+) monocytes when cultured with M‐CSF. Herein described is the discovery of an unexpected hematopoietic flexibility of a dominant population of multipotent myeloid cells, typically categorized as neutrophils, but with the previously unknown plasticity to contribute to mature pools of eosinophils and monocytes.

Introduction: Le Fort fractures comprise a pattern of complex midfacial fractures that arise secondarily to craniofacial trauma. Although management of these fractures has been detailed within the literature, there is a paucity of research examining postoperative outcomes after surgical repair. The primary aim of this study is to assess patient outcomes after operative management of Le Fort fractures, and examine factors influencing the risk for developing postoperative complications, through utilization of the ACS-NSQIP database. Methods: The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database was queried for cases recorded between 2012 and 2019 with International Classification of Disease (ICD)-9 and ICD-10 codes corresponding to Le Fort fractures. Patient demographics, clinical variables, and postoperative variables were recorded. Logistic regression analysis was conducted to identify independent risk factors for postoperative complications. Results: Identification of cases with appropriate ICD codes, and exclusion of those with missing data, yielded 562 patients for analysis. There were no cases of minor complications and 14 cases of severe complications (3 cases of wound dehiscence, 3 cases of transfusion requirement, 1 case of failure to wean from the ventilator for more than 48 h, 1 pulmonary embolism, and 8 cases of reoperation), corresponding to an overall complication rate of 2.49%. Logistic regression analysis revealed steroid use as an independent predictor of severe postoperative complications (OR = 13.73, 95% CI: 1.08-128.02, P = 0.02). Conclusion:The present study is the first to conduct a risk factor analysis of patients with Le Fort fractures using the ACS-NSQIP national database. The overall postoperative complication rate was 2.49%, with 14 cases of complications recorded in 8 years. Although this may suggest that surgical management of Le Fort fractures is generally well-tolerated, it should be noted that this problem is frequently associated with other severe injuries of the head and neck that may influence patient prognosis. Given this, further analysis would benefit from a larger patient cohort and longer postoperative data as the ACS-NSQIP database only records outcomes within 30 days.

Bone marrow is classically viewed as the major source of differentiated leukocytes infiltrating tissues from circulation. Recent evidence shows that the lung can potentially function as a hematopoietic organ on its own. This is a novel concept and tissue factors driving in situ leukocyte production are not yet well understood. In naïve murine lungs, we detected a small population of Lin−CD34+c-Kit+ common myeloid progenitors (CMPs) by flow cytometry and single cell RNA-seq analysis. Males had 0.087±0.06% CMPs, while females had a larger population of 0.18±0.08%, out of CD45+ cells. In a 3 challenge in vivo ovalbumin model of allergic inflammation, we observed a six-fold expansion of CMPs in the lung tissue and the appearance of Siglec-F+CD34+IL-5Rα+ eosinophil progenitors (EoPs) (1.505±0.6% of CD45+). To illustrate the hematopoietic potential of the lung independent of bone marrow recruitment, we cultured naïve lung single cell suspensions ex vivo in presence of SCF, FLT3 and IL-5. This was sufficient to yield up to 20% mature eosinophils, which is comparable to tissue eosinophil levels in models of allergic inflammation. We further tested whether Tenascin-C (TNC), a known component of bone marrow hematopoiesis, may equally support the hematopoietic niche in the lung. TNC is a provisional matrix glycoprotein that strongly associates with epithelial remodeling and eosinophil accumulation in asthma. TNC−/− mice had a significant defect in CMP and EoP expansion in a murine model of asthma and ex vivo IL-5 lung cultures. Administration of recombinant TNC rescued normal lung eosinophilopoiesis. These results suggest the existence and significant potential of the lung hematopoietic niche to supply effector cells during inflammation.