Neutrophils and galectin-3 defend mice from lethal bacterial infection and humans from acute respiratory failure.

Respiratory infection by Pseudomonas aeruginosa, common in hospitalized immunocompromised and immunocompetent ventilated patients, can be life-threatening because of antibiotic resistance. This raises the question of whether the host's immune system can be educated to combat this bacterium. Here we show that prior exposure to a single low dose of lipopolysaccharide (LPS) protects mice from a lethal infection by P. aeruginosa. LPS exposure trained the innate immune system by promoting expansion of neutrophil and interstitial macrophage populations distinguishable from other immune cells with enrichment of gene sets for phagocytosis- and cell-killing-associated genes. The cell-killing gene set in the neutrophil population uniquely expressed Lgals3, which encodes the multifunctional antibacterial protein, galectin-3. Intravital imaging for bacterial phagocytosis, assessment of bacterial killing and neutrophil-associated galectin-3 protein levels together with use of galectin-3-deficient mice collectively highlight neutrophils and galectin-3 as central players in LPS-mediated protection. Patients with acute respiratory failure revealed significantly higher galectin-3 levels in endotracheal aspirates (ETAs) of survivors compared to non-survivors, galectin-3 levels strongly correlating with a neutrophil signature in the ETAs and a prognostically favorable hypoinflammatory plasma biomarker subphenotype. Taken together, our study provides impetus for harnessing the potential of galectin-3-expressing neutrophils to protect from lethal infections and respiratory failure.

Macroscopic changes in aquaporin-4 underlie blast traumatic brain injury-related impairment in glymphatic function.

Mild traumatic brain injury (mTBI) has emerged as a potential risk factor for the development of neurodegenerative conditions such as Alzheimer's disease and chronic traumatic encephalopathy. Blast mTBI, caused by exposure to a pressure wave from an explosion, is predominantly experienced by military personnel and has increased in prevalence and severity in recent decades. Yet the underlying pathology of blast mTBI is largely unknown. We examined the expression and localization of AQP4 in human post-mortem frontal cortex and observed distinct laminar differences in AQP4 expression following blast exposure. We also observed similar laminar changes in AQP4 expression and localization and delayed impairment of glymphatic function that emerged 28 days following blast injury in a mouse model of repetitive blast mTBI. In a cohort of veterans with blast mTBI, we observed that blast exposure was associated with an increased burden of frontal cortical MRI-visible perivascular spaces, a putative neuroimaging marker of glymphatic perivascular dysfunction. These findings suggest that changes in AQP4 and delayed glymphatic impairment following blast injury may render the post-traumatic brain vulnerable to post-concussive symptoms and chronic neurodegeneration.

Clinical and economic outcomes associated with lymph node examination status in early-stage non-small cell lung cancer: a real-world US study using the SEER-Medicare linked database.

Background: Clinical practice guidelines recommend adjuvant therapy for patients with early non-small cell lung cancer (eNSCLC), especially those with lymph node metastasis. This study evaluated the prevalence of lymph node examination and its association with adjuvant treatment rates, overall survival (OS), and healthcare costs among United States (US) Medicare patients with resected eNSCLC. Methods: This retrospective observational cohort study used Surveillance, Epidemiology, and End Results cancer registry data linked with Medicare claims data. Eligible patients were aged ≥65 years with newly diagnosed non-small cell lung cancer (NSCLC) stages IA to IIIB [the American Joint Committee on Cancer (AJCC) Cancer Staging Manual, 7th edition] between January 2010 and December 2017 with surgery ≤1 month prior to or ≤12 months after diagnosis. Patients were grouped by lymph node examination status: no examination (pNX), examination and no metastasis (pN0), or metastasis staging in N1 (pN1) or N2 (pN2). OS and costs were evaluated by examination status and number of lymph node examined. OS was analyzed using extended Cox proportional hazards models for specific time periods and time interaction with examination status, and adjusted for patient characteristics. Adjusted post-surgical healthcare costs per patient per month (PPPM) were analyzed using gamma-log regression models. Results: Among the 14,648 patients included in the study, approximately 11% were pNX, whereas most were pN0 (68%), followed by pN1 (11%) and pN2 (10%). Adjuvant treatment rates were higher for pNX (35%) than pN0 (18%), but lower than pN1 (68%) and pN2 (74%) patients (P<0.001). Unadjusted OS for pNX patients was nearly identical to pN2, and significantly worse compared to pN0 and pN1 (P<0.0001). After adjusting for patient characteristics, pNX patients had higher risk of death relative to pN0 patients (P<0.001). Marginal mean adjusted total costs were comparable across pNX ($15,827 PPPM), pN0 ($12,712 PPPM) and pN1 ($17,089 PPPM), but significantly less for pN0 compared to pN2 ($23,566 PPPM) (P=0.002). Conclusions: Inadequate lymph node examination is associated with underutilization of adjuvant treatment and poor OS in resected NSCLC. In the current era of targeted and immunotherapies, lymph node examination is more important than ever, implicating the need for Quality Improvement practices and multidisciplinary coordination.

Increased Neutrophil H2O2 Production and Enhanced Pulmonary Clearance of Klebsiella pneumoniae in G6PD A- Mice.

The X-linked A- variant (rs1050828, Val68Met) in G6PDX accounts for glucose-6-phosphate (G6PD) deficiency in approximately 11% of African American males. This common, hypomorphic variant may impact pulmonary host defense and phagocyte function during pneumonia by altering levels of reactive oxygen species produced by host leukocytes. We used CRISPR-Cas9 technology to generate novel mouse strain with "humanized" G6PD A- variant containing non-synonymous Val68Met single nucleotide polymorphism. Male hemizygous or littermate wild-type (WT) controls were inoculated intratracheally with K. pneumoniae (KP2 serotype, ATCC 43816 strain,103 CFU inoculum). We examined leukocyte recruitment, organ bacterial burden, bone marrow neutrophil and macrophage (BMDM) phagocytic capacity, and hydrogen peroxide (H2O2) production. Unexpectedly, G6PD-deficient mice showed decreased lung bacterial burden (p=0.05) compared to controls 24-h post-infection. Extrapulmonary dissemination and bacteremia were significantly reduced in G6PD-deficient mice 48-h post-infection. Bronchoalveolar lavage fluid (BALF) IL-10 levels were elevated in G6PD-deficient mice (p=0.03) compared to controls at 24-h but were lower at 48-h (p=0.03). G6PD A- BMDMs show mildly decreased in vitro phagocytosis of pHrodo-labeled KP2 (p=0.03). Baseline, but not stimulated, H2O2 production by G6PD A- neutrophils was greater compared to WT neutrophils. G6PD A- variant demonstrate higher basal neutrophil H2O2 production and are protected against acute Klebsiella intrapulmonary infection.

Confidentiality in the Care of Adolescents: Policy Statement.

Confidentiality is an essential component of high-quality health care for adolescents and young adults and can have an impact on the health care experiences and health outcomes of youth. Federal and state laws, professional guidelines, and ethical standards provide a core framework for guidance in the implementation of confidentiality protections in clinical practice. This policy statement provides recommendations for pediatricians and other pediatric health care professionals, clinics, health systems, payers, and electronic health record developers to optimize confidentiality practices and protections for adolescents and young adults across the spectrum of care.

Pediatric Gender Diversity Beyond the Binary: An Exploration of Gender-Affirming Care for Nonbinary and Genderqueer Youth Seen Over Time at a Single Institution Gender Center.

Purpose: The nonbinary and genderqueer (NBGQ) youth population is growing, yet scant research focuses on this distinct group. We aim to gain a deeper understanding of desired gender-affirming care and interventions pursued by NBGQ youth. Methods: A retrospective chart review of NBGQ patients seen at the University of California, San Francisco Child and Adolescent Gender Center from January 1, 2009, to December 31, 2020, was performed. Demographic information, desired gender-affirming care, and gender-affirming interventions pursued at initial and most recent visits were collected. Results: Initial visit charts of 116 NBGQ youth who attended more than one clinic visit were reviewed. In total, 48 unique genders were documented; gender evolved over time for some youth, as did desired gender-affirming care. At the most recent visit, 15 youth (12.9%) had a binary gender, and 101 youth (87.1%) had an NBGQ gender. At the initial visit, 56 youth (48.3%) were interested in gender-affirming hormone therapy, compared with 75 youth (65.6%) at the most recent visit. In addition, 21 (18.1%) and 49 (42.2%) youth were interested in surgery at the initial and most recent visits, respectively. In general, interest in interventions was higher than pursuit of interventions. Conclusion: There is vast diversity of gender and differences in desired gender-affirming care within the NBGQ youth population. Desires for gender-affirming care within the cohort changed over time, and not all those who expressed a desire for an intervention received it. The reasons are likely multifactorial, highlighting the need for expectation-free and patient-specific affirming care and research on the NBGQ youth population, while also considering barriers to care.

Neurologic Dysphagia.

Dysphagia is commonly associated with neurologic/neuromuscular disorders including prematurity, cerebral palsy, traumatic brain injury, brain tumors, genetic disorders, and neuromuscular diseases. This article aims to review the major categories of neurologic dysphagia, to outline specific findings and special considerations for each population, and to acknowledge the importance of integrating each patient's medical prognosis, goals of care, and developmental stage into a multidisciplinary treatment plan.

Confidentiality in the Care of Adolescents: Technical Report.

Confidentiality is a foundational element of high-quality, accessible, and equitable health care. Despite strong grounding in federal and state laws, professional guidelines, and ethical standards, health care professionals and adolescent patients face a range of complexities and barriers to seeking and providing confidential care to adolescents across different settings and circumstances. The dynamic needs of adolescents, the oftentimes competing interests of key stakeholders, the rapidly evolving technological context of care, and variable health care billing and claims requirements are all important considerations in understanding how to optimize care to focus on and meet the needs of the adolescent patient. The following assessment of the evolving evidence base offers a view of the current state and best practices while pointing to numerous unmet needs and opportunities for improvement in the care experiences of youth as well as their health outcomes.

Laboratory Changes During Gender-Affirming Hormone Therapy in Transgender Adolescents.

OBJECTIVES: Guidelines for monitoring of medications frequently used in the gender-affirming care of transgender and gender-diverse (TGD) adolescents are based on studies in adults or other medical conditions. In this study, we aimed to investigate commonly screened laboratory measurements in TGD adolescents receiving gender-affirming hormone therapy (GAHT). METHODS: TGD adolescents were recruited from 4 study sites in the United States before beginning GAHT. Hemoglobin, hematocrit, hemoglobin A1c, alanine transaminase, aspartate aminotransferase, prolactin, and potassium were abstracted from the medical record at baseline and at 6, 12, and 24 months after starting GAHT. RESULTS: Two-hundred and ninety-three participants (68% designated female at birth) with no previous history of gonadotropin-releasing hormone analog use were included in the analysis. Hemoglobin and hematocrit decreased in adolescents prescribed estradiol (-1.4 mg/dL and -3.6%, respectively) and increased in adolescents prescribed testosterone (+1.0 mg/dL and +3.9%) by 6 months after GAHT initiation. Thirteen (6.5%) participants prescribed testosterone had hematocrit > 50% during GAHT. There were no differences in hemoglobin A1c, alanine transaminase, or aspartate aminotransferase. There was a small increase in prolactin after 6 months of estradiol therapy in transfeminine adolescents. Hyperkalemia in transfeminine adolescents taking spironolactone was infrequent and transient if present. CONCLUSIONS: Abnormal laboratory results are rare in TGD adolescents prescribed GAHT and, if present, occur within 6 months of GAHT initiation. Future guidelines may not require routine screening of these laboratory parameters beyond 6 months of GAHT in otherwise healthy TGD adolescents.

Validation of an Updated Algorithm to Identify Patients With Incident Non-Small Cell Lung Cancer in Administrative Claims Databases.

PURPOSE: Real-world lung cancer data in administrative claims databases often lack staging information and specific diagnostic codes for lung cancer histology subtypes. This study updates and validates Turner's 2017 treatment-based algorithm using more recent claims and electronic health record (EHR) data. METHODS: This study used Optum's deidentified Market Clarity Data of linked medical and pharmacy claims with EHR data. Eligible patients had an incident lung cancer diagnosis (January 2014-December 2020) and ≥one valid histology code for lung cancer 30 days before to 60 days after diagnosis. Histology and stage information from the EHR were used to evaluate the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV). We evaluated the Turner algorithm using cohort 1 patients diagnosed between June 2014 and October 2015 (step 1) and between November 2015 and December 2020 after approval of immunotherapies (step 2). Next, we evaluated cohort 2 patients diagnosed between November 2015 and December 2020 using an updated algorithm incorporating the latest US treatment guidelines (step 3), and compared the results for cohort 2 (Turner algorithm, step 2 patients). Furthermore, an algorithm to determine early NSCLC (eNSCLC; stage I-III) versus metastatic or advanced/metastatic non-small cell lung cancer (stage IV) was evaluated among patients with available histology and stage information. RESULTS: A total of 5,012 patients were included (cohort 1, step 1: n = 406; cohort 1, step 2: n = 2,573; cohort 2, step 3: n = 2,744). The updated algorithm showed improved performance relative to the previous Turner algorithm for sensitivity (0.920-0.932), specificity (0.865-0.923), PPV (0.976-0.988), and NPV (0.640-0.673). The eNSCLC algorithm showed high specificity (0.874) and relatively low sensitivity (0.539). CONCLUSION: An updated treatment-based algorithm identifying patients with incident NSCLC was validated using EHR data and distinguished lung cancer subtypes in claims databases when EHR data were not available.

Socioeconomic factors associated with uptake and satisfaction with a post-hospitalization meals benefit in Medicare Advantage.

BACKGROUND: Kaiser Permanente Southern California began offering a 4-week supplemental benefit of home-delivered meals to Medicare Advantage members after discharge from a hospitalization for heart failure and other medical conditions in 2021. The purpose of this study is to explore the associations between socioeconomic disadvantage and food insecurity with patient uptake of and satisfaction with the meals. METHODS: Data for this cross-sectional study were drawn from survey and electronic medical record data for members referred for the meals benefit (n = 6169) and linked to a hospitalization encounter (n = 2254) between January and December 2021. Uptake was assessed using vendor records; measures of socioeconomic status included the neighborhood deprivation index (NDI) and prior receipt of medical financial assistance (MFA) from the health system. Patients were invited to complete an email or phone survey about their satisfaction with the meals and food insecurity. Multivariable log-binomial regression models were used to examine the association between socioeconomic disadvantage and food insecurity with meals uptake and satisfaction. RESULTS: Sixty-two percent of patients referred for the benefit accepted the meals (mean age: 79 ± 9, 59% people of color). While there was no significant relationship between NDI and meals uptake (RR: 0.99, 95% CI: 0.92-1.07, p = 0.77), patients who received prior MFA were more likely to accept the meals (RR: 1.09, 95% CI: 1.02-1.16, p < 0.01). Sixty-nine percent of patients who completed the survey (23% response rate) reported that meals were very or extremely helpful. Patients with food insecurity (29% of survey respondents) were more likely to report that the meals were helpful for their recovery compared to food secure patients (RR: 1.21, 95% CI: 1.09-1.35, p < 0.01). CONCLUSIONS: The home-delivered meals appeared to be particularly utilized by and helpful to patients with greater financial strain and/or food insecurity, suggesting that supplemental benefits could be more targeted toward addressing unmet needs of vulnerable adults.

Association Between Intensity and Timing of Specialty Palliative Care and Hospice Exposure With Quality of End-of-Life Care.

Background: Gaps remain in our understanding of the intensity and timing of specialty palliative care (SPC) exposure on end-of-life (EOL) outcomes. Objective: Examine the association between intensity and timing of SPC and hospice (HO) exposure on EOL care outcomes. Design, Settings, Participants: Data for this cohort study were drawn from 2021 adult decedents from Kaiser Permanente Southern California and Colorado (n = 26,251). Caregivers of a decedent subgroup completed a postdeath care experience survey from July to August 2022 (n = 424). Measurements: SPC intensity (inpatient, outpatient, and home-based) and HO exposure in the five years before death were categorized as: (1) No SPC or HO; (2) SPC-only; (3) HO-only; and (4) SPC-HO. Timing of SPC exposure (<90 or 90+ days) before death was stratified by HO enrollment. Death in the hospital and potentially burdensome treatments in the last 14 days of life were extracted from electronic medical records (EMRs) and claims. EOL care experience was obtained from the caregiver survey. Results: Among the EMR cohort, exposure to SPC and HO were: No SPC or HO (38%), SPC-only (14%; of whom, 55% received inpatient SPC only), HO-only (20%), and SPC-HO (28%). For decedents who did not enroll in HO, exposure to SPC 90+ days versus <90 days before death was associated with lower risk of receiving potentially burdensome treatments (adjusted relative risk, aRR: 0.69 [95% confidence interval, CI: 0.62-0.76], p < 0.001) and 23% lower risk of dying in the hospital (aRR: 0.77 [95% CI: 0.73-0.81], p < 0.001). Caregivers of patients in the HO-only (aRR: 1.27 [95% CI: 0.98-1.63], p = 0.07) and SPC-HO cohorts (aRR: 1.19 [95% CI: 0.93-1.52], p = 0.18) tended to report more positive care experience compared to the no SPC or HO cohort. Conclusion: Earlier exposure to SPC was important in reducing potentially burdensome treatments and death in the hospital for decedents who did not enroll in HO. Increasing availability and access to community-based SPC is needed.

Siderophores promote cooperative interspecies and intraspecies cross-protection against antibiotics in vitro.

The antibiotic cefiderocol hijacks iron transporters to facilitate its uptake and resists ß-lactamase degradation. While effective, resistance has been detected clinically with unknown mechanisms. Here, using experimental evolution, we identified cefiderocol resistance mutations in Pseudomonas aeruginosa. Resistance was multifactorial in host-mimicking growth media, led to multidrug resistance and paid fitness costs in cefiderocol-free environments. However, kin selection drove some resistant populations to cross-protect susceptible individuals from killing by increasing pyoverdine secretion via a two-component sensor mutation. While pyochelin sensitized P. aeruginosa to cefiderocol killing, pyoverdine and the enterobacteria siderophore enterobactin displaced iron from cefiderocol, preventing uptake by susceptible cells. Among 113 P. aeruginosa intensive care unit clinical isolates, pyoverdine production directly correlated with cefiderocol tolerance, and high pyoverdine producing isolates cross-protected susceptible P. aeruginosa and other Gram-negative bacteria. These in vitro data show that antibiotic cross-protection can occur via degradation-independent mechanisms and siderophores can serve unexpected protective cooperative roles in polymicrobial communities.

Functional effects of an African glucose-6-phosphate dehydrogenase (G6PD) polymorphism (Val68Met) on red blood cell hemolytic propensity and post-transfusion recovery.

BACKGROUND: Donor genetic variation is associated with red blood cell (RBC) storage integrity and post-transfusion recovery. Our previous large-scale genome-wide association study demonstrated that the African G6PD deficient A- variant (rs1050828, Val68Met) is associated with higher oxidative hemolysis after cold storage. Despite a high prevalence of X-linked G6PD mutation in African American population (>10%), blood donors are not routinely screened for G6PD status and its importance in transfusion medicine is relatively understudied. STUDY DESIGN AND METHODS: To further evaluate the functional effects of the G6PD A- mutation, we created a novel mouse model carrying this genetic variant using CRISPR-Cas9. We hypothesize that this humanized G6PD A- variant is associated with reduced G6PD activity with a consequent effect on RBC hemolytic propensity and post-transfusion recovery. RESULTS: G6PD A- RBCs had reduced G6PD protein with ~5% residual enzymatic activity. Significantly increased in vitro hemolysis induced by oxidative stressors was observed in fresh and stored G6PD A- RBCs, along with a lower GSH:GSSG ratio. However, no differences were observed in storage hemolysis, osmotic fragility, mechanical fragility, reticulocytes, and post-transfusion recovery. Interestingly, a 14% reduction of 24-h survival following irradiation was observed in G6PD A- RBCs compared to WT RBCs. Metabolomic assessment of stored G6PD A- RBCs revealed an impaired pentose phosphate pathway (PPP) with increased glycolytic flux, decreasing cellular antioxidant capacity. DISCUSSION: This novel mouse model of the common G6PD A- variant has impaired antioxidant capacity like humans and low G6PD activity may reduce survival of transfused RBCs when irradiation is performed.

Effectiveness and safety of early treatment with spironolactone for new-onset acute heart failure.

BACKGROUND: The effectiveness and safety of mineralocorticoid receptor antagonists (MRA) in acute heart failure (HF) is uncertain. We sought to describe the prescription of spironolactone during acute HF and whether early treatment is effective and safe in a real-world setting. METHODS: We performed a retrospective cohort study of adult (≥18 years) nonpregnant patients hospitalized with new-onset HF with reduced ejection fraction (HFrEF, defined by ejection fraction ≤40%) within 15 Kaiser Permanente Southern California medical centers between 2016 and 2021. Early treatment was defined by spironolactone prescription at discharge. The primary effectiveness outcome was a composite of HF readmission or all-cause mortality at 180 days. Safety outcomes were hypotension and hyperkalemia at 90 days. RESULTS: Among 2318 HFrEF patients, 368 (15.9%) were treated with spironolactone at discharge. After 1:2 propensity score matching, 354 early treatment and 708 delayed/no treatment patients were included in the analysis. The median age was 63 (IQR: 52-74) years; 61.6% were male, and 38.6% were White. By 90 days, ~20% had crossed over in the two groups. Early treatment was not associated with the composite outcome at 180 days (HR [95% CI]: 0.81 [0.56-1.17]), but a trend towards benefit by 365 days that did not reach statistical significance (0.78 [0.58-1.06]). Early treatment was also associated with hyperkalemia (subdistribution HR [95% CI]: 2.33 [1.30-4.18]) but not hypotension (0.93 [0.51-1.72]). CONCLUSIONS: Early treatment with spironolactone at discharge for new-onset HFrEF in a real-world setting did not reduce the risk of HF readmission or mortality in the first year after discharge. The risk of hyperkalemia was increased.

Lung Epithelium Releases Growth Differentiation Factor 15 in Response to Pathogen-mediated Injury.

GDF15 (growth differentiation factor 15) is a stress cytokine with several proposed roles, including support of stress erythropoiesis. Higher circulating GDF15 levels are prognostic of mortality during acute respiratory distress syndrome, but the cellular sources and downstream effects of GDF15 during pathogen-mediated lung injury are unclear. We quantified GDF15 in lower respiratory tract biospecimens and plasma from patients with acute respiratory failure. Publicly available data from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were reanalyzed. We used mouse models of hemorrhagic acute lung injury mediated by Pseudomonas aeruginosa exoproducts in wild-type mice and mice genetically deficient for Gdf15 or its putative receptor, Gfral. In critically ill humans, plasma levels of GDF15 correlated with lower respiratory tract levels and were higher in nonsurvivors. SARS-CoV-2 infection induced GDF15 expression in human lung epithelium, and lower respiratory tract GDF15 levels were higher in coronavirus disease (COVID-19) nonsurvivors. In mice, intratracheal P. aeruginosa type II secretion system exoproducts were sufficient to induce airspace and plasma release of GDF15, which was attenuated with epithelial-specific deletion of Gdf15. Mice with global Gdf15 deficiency had decreased airspace hemorrhage, an attenuated cytokine profile, and an altered lung transcriptional profile during injury induced by P. aeruginosa type II secretion system exoproducts, which was not recapitulated in mice deficient for Gfral. Airspace GDF15 reconstitution did not significantly modulate key lung cytokine levels but increased circulating erythrocyte counts. Lung epithelium releases GDF15 during pathogen injury, which is associated with plasma levels in humans and mice and can increase erythrocyte counts in mice, suggesting a novel lung-blood communication pathway.

STAT1 Employs Myeloid Cell-Extrinsic Mechanisms to Regulate the Neutrophil Response and Provide Protection against Invasive Klebsiella pneumoniae Lung Infection.

Klebsiella pneumoniae (KP) is an extracellular Gram-negative bacterium that causes infections in the lower respiratory and urinary tracts and the bloodstream. STAT1 is a master transcription factor that acts to maintain T cell quiescence under homeostatic conditions. Although STAT1 helps defend against systemic spread of acute KP intrapulmonary infection, whether STAT1 regulation of T cell homeostasis impacts pulmonary host defense during acute bacterial infection and injury is less clear. Using a clinical KP respiratory isolate and a pneumonia mouse model, we found that STAT1 deficiency led to an early neutrophil-dominant transcriptional profile and neutrophil recruitment in the lung preceding widespread bacterial dissemination and lung injury development. Yet, myeloid cell STAT1 was dispensable for control of KP proliferation and dissemination, because myeloid cell-specific STAT1-deficient (LysMCre/WT;Stat1fl/fl) mice showed bacterial burden in the lung, liver, and kidney similar to that of their wild-type littermates. Surprisingly, IL-17-producing CD4+ T cells infiltrated Stat1-/- murine lungs early during KP infection. The increase in Th17 cells in the lung was not due to preexisting immunity against KP and was consistent with circulating rather than tissue-resident CD4+ T cells. However, blocking global IL-17 signaling with anti-IL-17RC administration led to increased proliferation and dissemination of KP, suggesting that IL-17 provided by other innate immune cells is essential in defense against KP. Contrastingly, depletion of CD4+ T cells reduced Stat1-/- murine lung bacterial burden, indicating that early CD4+ T cell activation in the setting of global STAT1 deficiency is pathogenic. Altogether, our findings suggest that STAT1 employs myeloid cell-extrinsic mechanisms to regulate neutrophil responses and provides protection against invasive KP by restricting nonspecific CD4+ T cell activation and immunopathology in the lung.