Specific Inhibition of Orai1-mediated Calcium Signalling Resolves Inflammation and Clears Bacteria in an Acute Respiratory Distress Syndrome Model

Rationale: Acute respiratory distress syndrome (ARDS) has an unacceptably high mortality rate (35%) and is without effective therapy. Orai1 is a Ca2+ channel involved in store-operated Ca2+ entry (SOCE), a process that exquisitely regulates inflammation. Orai1 is considered a druggable target, but no Orai1-specific inhibitors exist to date. Objectives: To evaluate whether ELD607, a first-in-class Orai1 antagonist, can treat ARDS caused by bacterial pneumonia in preclinical models. Methods: ELD607 pharmacology was evaluated in HEK293T cells and freshly isolated immune cells from patients with ARDS. A murine acute lung injury model caused by bacterial pneumonia was then used: mice were infected with Pseudomonas aeruginosa, Staphylococcus aureus, methicillin-resistant S. aureus, or multidrug-resistant P. aeruginosa and then treated with ELD607 intranasally. Measurements and Main Results: ELD607 specifically inhibited SOCE in HEK293T cells with a half-maximal inhibitory concentration of 9 nM. ELD607 was stable in ARDS airway secretions and inhibited SOCE in ARDS immune cells. In vivo, inhaled ELD607 significantly reduced neutrophilia and improved survival. Surprisingly, Orai1 inhibition by ELD607 caused a significant reduction in lung bacteria, including methicillin-resistant S. aureus. ELD607 worked as an immunomodulator that reduced cytokine levels, reduced neutrophilia, and promoted macrophage-mediated resolution of inflammation and clearance of bacteria. Indeed, when alveolar macrophages were depleted with inhaled clodronate, ELD607 was no longer able to resolve inflammation or clear bacteria. Conclusions: These data indicate that specific Orai1 inhibition by ELD607 may be a novel approach to reduce multiorgan inflammation and treat antibiotic-resistant bacteria.

Systemic THrombolysis Randomization IN Endovascular Stroke Therapy (SHRINE) Collaboration: a patient-level pooled analysis of the SKIP and DEVT Trials

OBJECTIVE

To evaluate the non-inferiority of endovascular treatment (EVT) alone versus intravenous thrombolysis (IVT) followed by EVT and to assess its heterogeneity across prespecified subgroups.

METHODS

We pooled data from two trials (SKIP in Japan; DEVT in China). Individual patient data were pooled to assess outcomes and heterogeneity of treatment effect. The primary outcome was functional independence (modified Rankin Scale score 0-2) at 90 days. Safety outcomes included symptomatic intracranial hemorrhage (sICH) and 90-day mortality.

RESULTS

We included 438 patients (217 EVT alone; 221 combined IVT+EVT). The meta-analysis failed to demonstrate the non-inferiority of EVT alone over combined IVT+EVT in achieving 90-day functional independence (56.7% vs 51.6%; adjusted common odds ratio (cOR)=1.27, 95% CI 0.84 to 1.92, pnon-inferiority=0.06). Effect sizes favoring EVT alone were present with stroke onset to puncture time longer than 180 min (cOR=2.28, 95% CI 1.18 to 4.38, pinteraction ≤180 vs >180 min=0.02) and intracranial internal carotid artery ICA occlusions (for ICA cOR=3.04, 95% CI 1.10 to 8.43, pinteraction ICA vs MCA=0.08). The rates of sICH (6.5% vs 9.0%; cOR=0.77, 95% CI 0.37 to 1.61) and 90-day mortality (12.9% vs 13.6%; cOR=1.05, 95% CI 0.58 to 1.89) were comparable.

CONCLUSIONS

The cumulative data of these two recent Asian trials failed to unequivocally demonstrate the non-inferiority of EVT alone over combined IVT+EVT. However, our study suggests a potential role for more individualized decision-making. Specifically, Asian patients with stroke onset to EVT longer than 180 min, as well as those with intracranial ICA occlusions and those with atrial fibrillation might have better outcomes with EVT alone than with combined IVT+EVT.

Different airborne particulates trigger distinct immune pathways leading to peanut allergy in a mouse model

BACKGROUND

Environmental exposure to peanut through non-oral routes is a risk factor for peanut allergy. Early-life exposure to air pollutants, including particulate matter (PM), is associated with sensitization to foods through unknown mechanisms. We investigated whether PM promotes sensitization to environmental peanut and the development of peanut allergy in a mouse model.

METHODS

C57BL/6J mice were co-exposed to peanut and either urban particulate matter (UPM) or diesel exhaust particles (DEP) via the airways and assessed for peanut sensitization and development of anaphylaxis following peanut challenge. Peanut-specific CD4+ T helper (Th) cell responses were characterized by flow cytometry and Th cytokine production. Mice lacking select innate immune signaling genes were used to study mechanisms of PM-induced peanut allergy.

RESULTS

Airway co-exposure to peanut and either UPM- or DEP-induced systemic sensitization to peanut and anaphylaxis following peanut challenge. Exposure to UPM or DEP triggered activation and migration of lung dendritic cells to draining lymph nodes and induction of peanut-specific CD4+ Th cells. UPM- and DEP-induced distinct Th responses, but both stimulated expansion of T follicular helper (Tfh) cells essential for peanut allergy development. MyD88 signaling was critical for UPM- and DEP-induced peanut allergy, whereas TLR4 signaling was dispensable. DEP-induced peanut allergy and Tfh-cell differentiation depended on IL-1 but not IL-33 signaling, whereas neither cytokine alone was necessary for UPM-mediated sensitization.

CONCLUSION

Environmental co-exposure to peanut and PM induces peanut-specific Tfh cells and peanut allergy in mice.

A single priming event prevents oral tolerance to peanut

BACKGROUND

Indoor dust (ID) is a source of peanut proteins and immunostimulatory adjuvants (e.g. LPS) that can promote airway sensitization to peanut. We aimed to determine whether a single airway exposure to peanut plus adjuvant is sufficient to prevent oral tolerance.

METHODS

To determine the effect of a single priming event, C57BL/6J mice were exposed once to peanut plus adjuvant through the airway, followed by either airway or low-dose oral exposure to peanut, and assessed for peanut allergy. Oral tolerance was investigated by feeding high-dose peanut followed by airway sensitization. To determine whether a single priming could prevent oral tolerance, the high-dose peanut regimen was applied after a single airway exposure to peanut plus adjuvant. Peanut-specific IgE and IgG1 were quantified, and mice were challenged to peanut to assess allergy. Peanut-specific CD4+ memory T cells (CD4+ TCRβ+ CD44hi CD154+ ) were quantified in mediastinal lymph nodes following airway priming.

RESULTS

Mice co-exposed to peanut with LPS or ID through the airway were primed to develop peanut allergy after subsequent low-dose oral or airway exposures to peanut. Oral tolerance was induced in mice fed high-dose peanut prior to airway sensitization. In contrast, mice fed high-dose peanut following a single airway exposure to peanut plus adjuvant led to allergy. Peanut-specific CD4+ memory T cells were detected as early as 7 days after the single airway priming with peanut plus adjuvant, however, delaying peanut feeding even 1 day following priming led to allergy, whereas peanut feeding the same day as priming led to tolerance.

CONCLUSIONS

A single airway exposure to peanut plus adjuvant is sufficient to prime the immune system to develop allergy following subsequent high-dose oral exposure. These results highlight the importance of introducing peanut as early as possible to prevent sensitization through a non-oral priming event.

Use of nonstigmatizing language is associated with improved outcomes in hospitalized people who inject drugs

BACKGROUND

Stigma surrounding opioid use disorder (OUD) is a barrier to treatment. The use of stigmatizing language may be evidence of negative views toward patients.

OBJECTIVE

We aimed to identify associations between language and clinical outcomes in patients admitted for infectious complications of OUD.

DESIGNS

We performed a retrospective medical record review.

SETTINGS AND PARTICIPANTS

Four U.S. academic health systems. Participants were patients with OUD admitted for infectious complications of injection opioid use from January 1, 2018, to December 31, 2018, identified through international classification of diseases, 10th revision codes consistent with OUD and acute bacterial/fungal infection.

MAIN OUTCOME AND MEASURES

Discharge summaries were reviewed for language, specifically: abuse, addiction, dependence, misuse, use disorder, intravenous drug use, and others. Binary outcomes including medication for OUD, planned discharge, naloxone provision, and an OUD treatment plan were evaluated using logistic regressions and admission duration was evaluated using Gamma regression.

RESULTS

A total of 1285 records were reviewed and 328 met inclusion criteria. Of those, 191 (58%) were male, with a median age of 38 years. The most common term was "abuse" (219, 67%), whereas "use disorder" was recorded in 75 (23%) records. Having "use disorder" in the discharge summary was associated with increased odds of having a documented plan for ongoing OUD treatment (adjusted odds ratio [AOR]: 4.11, 95% confidence interval [CI]: 1.89-8.93) and having a documented plan for addiction-specific follow-up care (AOR: 2.31, 95% CI: 1.30-4.09).

CONCLUSIONS

Stigmatizing language was common in this study of patients hospitalized for infectious complications of OUD. Best-practice language was uncommon, but when used was associated with increased odds of addiction treatment and specialty care referrals.

Peanut butter feeding induces oral tolerance in genetically diverse collaborative cross mice

Background

Early dietary introduction of peanut has shown efficacy in clinical trials and driven pediatric recommendations for early introduction of peanut to children with heightened allergy risk worldwide. Unfortunately, tolerance is not induced in every case, and a subset of patients are allergic prior to introduction. Here we assess peanut allergic sensitization and oral tolerance in genetically diverse mouse strains.

Objective

We aimed to determine whether environmental adjuvant-driven airway sensitization and oral tolerance to peanut could be induced in various genetically diverse mouse strains.

Methods

C57BL/6J and 12 Collaborative Cross (CC) mouse strains were fed regular chow or ad libitum peanut butter to induce tolerance. Tolerance was tested by attempting to sensitize mice via intratracheal exposure to peanut and lipopolysaccharide (LPS), followed by intraperitoneal peanut challenge. Peanut-specific immunoglobulins and peanut-induced anaphylaxis were assessed.

Results

Without oral peanut feeding, most CC strains (11/12) and C57BL/6J induced peanut-specific IgE and IgG1 following airway exposure to peanut and LPS. With oral peanut feeding none of the CC strains nor C57BL/6J mice became sensitized to peanut or experienced anaphylaxis following peanut challenge.

Conclusion

Allergic sensitization and oral tolerance to peanut can be achieved across a range of genetically diverse mice. Notably, the same strains that became allergic via airway sensitization were tolerized by feeding high doses of peanut butter before sensitization, suggesting that the order and route of peanut exposure are critical for determining the allergic fate.

Collaborative cross strain CC011/UncJ as a novel mouse model of T2-high, severe asthma

Among asthmatics, there is significant heterogeneity in the clinical presentation and underlying pathophysiological mechanisms, leading to the recognition of multiple disease endotypes (e.g., T2-high vs. T2-low). This heterogeneity extends to severe asthmatics, who may struggle to control symptoms even with high-dose corticosteroid treatment and other therapies. However, there are limited mouse models available to model the spectrum of severe asthma endotypes. We sought to identify a new mouse model of severe asthma by first examining responses to chronic allergen exposure among strains from the Collaborative Cross (CC) mouse genetics reference population, which contains greater genetic diversity than other inbred strain panels previously used for models of asthma. Mice from five CC strains and the often-used classical inbred strain BALB/cJ were chronically exposed to house dust mite (HDM) allergen for five weeks followed by measurements of airway inflammation. CC strain CC011/UncJ (CC011) exhibited extreme responses to HDM including high levels of airway eosinophilia, elevated lung resistance, and extensive airway wall remodeling, and even fatalities among ~ 50% of mice prior to study completion. Compared to BALB/cJ mice, CC011 mice had stronger Th2-mediated airway responses demonstrated by significantly elevated total and HDM-specific IgE and increased Th2 cytokines during tests of antigen recall, but not enhanced ILC2 activation. Airway eosinophilia in CC011 mice was completely dependent upon CD4⁺ T-cells. Notably, we also found that airway eosinophilia in CC011 mice was resistant to dexamethasone steroid treatment. Thus, the CC011 strain provides a new mouse model of T2-high, severe asthma driven by natural genetic variation likely acting through CD4⁺ T-cells. Future studies aimed at determining the genetic basis of this phenotype will provide new insights into mechanisms underlying severe asthma.

Impact of the exposome on food allergy development

PURPOSE OF REVIEW

The increasing global prevalence of food allergy indicates that environmental exposures are likely contributing to food allergy development. This review summarizes recent studies on how specific factors within the external exposome may impact the development of food allergy.

RECENT FINDINGS

There is strong evidence that nonoral exposure to food allergens within the living environment is a risk factor for food sensitization and food allergy. The role of air pollution in food allergy development remains unclear, as cohort studies have not found consistent relationships between air pollutant exposure and food sensitization. Early-life microbial exposures linked to a rural lifestyle are likely protective against food allergy development, possibly through alteration of the infant microbiome. In contrast, factors associated with urbanization and decreased exposure to microbes may contribute to food allergy development. Recent studies on the role of residential greenness in food allergy development suggest either no relationship or a possible increased risk for food allergy.

SUMMARY

The external exposome comprises a number of exposures that can modify food allergy risk. Improved understanding of how complex environmental exposures interact with genetic factors will be necessary for developing effective interventions aimed at preventing food allergy development in children.

Representation of patients with non-English language preferences in motor vehicle collision trauma and emergency medicine research

BACKGROUND

Individuals with non-English language preferences (NELP) represent a growing proportion of the USA population. Prior studies demonstrate disparate health outcomes related to NELP status; however, this patient population is often excluded from medical research. There is a paucity of literature describing the impact of NELP status on trauma, specifically injury and outcomes related to vehicle occupants injured during motor vehicle collisions (MVCs). The goal of this study was to evaluate the representation of patients with NELP in both emergency medicine and trauma literature.

METHODS

We conducted a systematic search of US-based publications from 2010 to 2021. Titles, abstracts and full texts of eligible articles were evaluated. Data were extracted using an a priori determined standardised reporting tool to evaluate language as study inclusion/exclusion criteria, manuscript reporting of language, assessment of language as a primary variable and consideration of language in study methodology.

RESULTS

A total of 82 studies met inclusion criteria. Twenty-three studies (28%) excluded NELP populations and only one study explicitly included the NELP population. None of the studies evaluated language as a primary outcome of the study or included language as a variable in the analysis. Over half of the studies (53.6%) used a public data set or registry.

CONCLUSION

NELP populations are routinely excluded from and are difficult to identify in MVC trauma research. Without appropriate inclusion and identification, it will be difficult to understand the prevalence and outcomes of traumatic injury in NELP patients and to develop culturally and linguistically appropriate interventions.

Neuropilin‐2 regulates airway inflammation in a neutrophilic asthma model

Background

Asthma is a heterogenous disease that can be classified into eosinophilic (type 2‐high) and noneosinophilic (type 2‐low) endotypes. The type 2‐low endotype of asthma can be characterized by the presence of neutrophilic airway inflammation that is poorly responsive to corticosteroids. Dysregulated innate immune responses to microbial products including Toll‐like receptor (TLR) ligands have been associated with the pathogenesis of neutrophilic asthma. The key molecules that regulate inflammatory responses in individuals with neutrophilic asthma remain unclear. We previously reported that the immunoregulatory receptor neuropilin‐2 (NRP2) is expressed by murine and human alveolar macrophage (AM) and suppresses lipopolysaccharide (LPS)‐induced neutrophilic airway inflammation.

Methods

Here, we investigated the immunoregulatory role of NRP2 in a mouse model of neutrophilic asthma.

Results

We found that TLR ligands, but not T helper 2 (Th2)‐promoting adjuvants, induced NRP2 expression by AM. Using an LPS‐mediated model of neutrophilic asthma, we demonstrate that NRP2 was increased in AM and other lung antigen‐presenting cells following airway challenge with antigen. Conditional deletion of NRP2 in myeloid cells exacerbated airway inflammation in a neutrophilic asthma model. In contrast, myeloid‐specific ablation of NRP2 did not affect airway inflammation in a Th2‐mediated eosinophilic asthma model. Myeloid‐specific ablation of NRP2 did not affect Th1/Th17 responses to inhaled antigens or expression of neutrophil chemokines but rather resulted in impaired efferocytosis by AM, which is necessary for effective resolution of airway inflammation.

Conclusion

Our findings suggest that NRP2 is a negative regulator of airway inflammation associated with neutrophilic asthma.

Integrative analysis reveals mouse strain-dependent responses to acute ozone exposure associated with airway macrophage transcriptional activity

Acute ozone (O3) exposure is associated with multiple adverse cardiorespiratory outcomes, the severity of which varies across individuals in human populations and inbred mouse strains. However, molecular determinants of response, including susceptibility biomarkers that distinguish who will develop severe injury and inflammation, are not well characterized. We and others have demonstrated that airway macrophages (AMs) are an important resident immune cell type that are functionally and transcriptionally responsive to O3 inhalation. Here, we sought to explore influences of strain, exposure, and strain-by-O3 exposure interactions on AM gene expression and identify transcriptional correlates of O3-induced inflammation and injury across six mouse strains, including five Collaborative Cross (CC) strains. We exposed adult mice of both sexes to filtered air (FA) or 2 ppm O3 for 3 h and measured inflammatory and injury parameters 21 h later. Mice exposed to O3 developed airway neutrophilia and lung injury with strain-dependent severity. In AMs, we identified a common core O3 transcriptional response signature across all strains, as well as a set of genes exhibiting strain-by-O3 exposure interactions. In particular, a prominent gene expression contrast emerged between a low- (CC017/Unc) and high-responding (CC003/Unc) strain, as reflected by cellular inflammation and injury. Further inspection indicated that differences in their baseline gene expression and chromatin accessibility profiles likely contribute to their divergent post-O3 exposure transcriptional responses. Together, these results suggest that aspects of O3-induced respiratory responses are mediated through altered AM transcriptional signatures and further confirm the importance of gene-environment interactions in mediating differential responsiveness to environmental agents.

1362. Adding Insult to Injury: Association of Stigmatizing Language and Suboptimal Outcomes in People Who Inject Drugs

Background

The National Academy of Medicine has identified stigma surrounding substance use disorders (SUDs) and infectious diseases (ID) as a key barrier to integration of opioid use disorder (OUD) and ID services. Prior literature on stigmatizing language in OUD clinical care focuses on surveys and theoretical scenarios rather than real-world data. As part of a larger study of patients admitted for infectious complications of injection drug use (CHOICE), we sought to determine how inpatient physicians describe persons with OUD, as well as associations of this language with outcomes along the OUD continuum of care.

Methods

CHOICE is a retrospective review of adults hospitalized with an infectious complication of OUD and IDU at four academic medical centers. Included patients were hospitalized between 1/1/2018-12/31/2018, had ICD9/10 diagnosis codes consistent with OUD and acute bacterial/fungal infection, and chart review verification of active infection associated with OUD. Data was abstracted regarding demographics, inpatient interventions, transitions of care, and outcomes 1 year after admission. Potentially stigmatizing language was identified based on the discharge summary. “Abuse” and “misuse” were considered potentially stigmatizing; “use disorder” was considered best practice. Associations of language and outcomes were analyzed via logistic generalized estimating equations.

Results

A total of 287 subjects met inclusion criteria; 119 (42%) were female and the median age was 40 years (IQR: 32 – 52). The most common terms used to describe OUD were “abuse” (190, 66%) and “IVDU” (119, 42%). “Use disorder” was noted in only 72 (25%) charts. In a regression analysis, any mention of “use disorder” was associated with not leaving against medical advice (OR 2.48, 95% CI 1.24 – 4.95), a plan for ongoing OUD treatment (OR 5.17, 95% CI 2.05-13.0), and addiction-specific follow up (OR 2.94, 95% CI 2.34-3.68).

Conclusion

In this multicenter retrospective study, inpatient physicians commonly referred to patients with OUD using stigmatizing language. When NIH-preferred language was used this was associated with improved outcomes along the OUD continuum of care, possibly reflecting increased awareness of best practices for treating patients with OUD.

Disclosures

Ellen Eaton, MD , Gilead (Grant/Research Support) Ellen Eaton, MD , Gilead (Individual(s) Involved: Self): Research Grant or Support Greer A. Burkholder, MD, MSPH, Eli Lilly (Grant/Research Support) Sarah Kattakuzhy, MD, Gilead Sciences (Scientific Research Study Investigator, Research Grant or Support) Elana S. Rosenthal, MD, Gilead Sciences (Research Grant or Support)Merck (Research Grant or Support)

Monitored anesthesia care during mechanical thrombectomy for stroke: need for data-driven and individualized decisions

BACKGROUND

The optimal anesthesia management for patients with stroke undergoing mechanical thrombectomy (MT) during the COVID-19 pandemic has become a matter of controversy. Some recent guidelines have favored general anesthesia (GA) in patients perceived as high risk for intraprocedural conversion from sedation to GA, including those with dominant hemispheric occlusions/aphasia or baseline National Institutes of Health Stroke Scale (NIHSS) score >15. We aim to identify the rate and predictors of conversion to GA during MT in a high-volume center where monitored anesthesia care (MAC) is the default modality.

METHODS

A retrospective review of a prospectively maintained MT database from January 2013 to July 2020 was undertaken. Analyses were conducted to identify the predictors of intraprocedural conversion to GA. In addition, we analyzed the GA conversion rates in subgroups of interest.

RESULTS

Among 1919 MT patients, 1681 (87.6%) started treatment under MAC (median age 65 years (IQR 55-76); baseline NIHSS 16 (IQR 11-21); 48.4% women). Of the 1677 eligible patients, 26 (1.6%) converted to GA including 1.4% (22/1615) with anterior and 6.5% (4/62) with posterior circulation strokes. The only predictor of GA conversion was posterior circulation stroke (OR 4.99, 95% CI 1.67 to 14.96, P=0.004). The conversion rates were numerically higher in right than in left hemispheric occlusions (1.6% vs 1.2%; OR 1.37, 95% CI 0.59 to 3.19, P=0.47) and in milder than in more severe strokes (NIHSS ≤15 vs >15: 2% vs 1.2%; OR 0.62, 95% CI 0.28 to 1.36, P=0.23).

CONCLUSIONS

Our study showed that the overall rate of conversion from MAC to GA during MT was low (1.6%) and, while higher in posterior circulation strokes, it was not predicted by either hemispheric dominance or stroke severity. Caution should be given before changing clinical practice during moments of crisis.

Feasibility of a screening tool for sex trafficking in an adult emergency department

BACKGROUND

Human trafficking (HT) is a human rights violation and public health issue. People with a history of HT are likely to see a physician during their exploitation. A screening tool was developed and implemented in a busy urban emergency department (ED) to aid in the identification of this population.

OBJECTIVE

The objective was to retrospectively assess a HT screening tool implemented in an urban ED and evaluate the feasibility of the tool as a component of standard emergency care.

METHODS

This was a retrospective observational study conducted at an urban adult ED after the implementation of an original 11-item HT screening tool. Adult patients 18 years and older were screened based on high-risk chief complaints, "red flag" risk factors, or provider gestalt. All patients with a positive screen were offered the opportunity to speak to a social worker, who then determined the patients' likely trafficking status. Data analysis was performed on this group of patients.

RESULTS

A total of 26,974 patients were screened in the ED during 2019. Of these patients, 189 of them had a positive screen. A total of 37 patients were confirmed to have a likely sex trafficking status based on the federal definition. Eight of these patients elected to go to a community partner safe house. Positive responses to eight of the questions were significantly associated with likely sex trafficking status. Through regularized regression analysis, the predictive power of the screen was found to be derived from seven of the questions.

CONCLUSION

Through the implementation of this screening tool, providers in a busy urban ED were able to identify patients with an experience of sex trafficking and offer them resources using a trauma-informed approach. This study demonstrates the feasibility of implementation of screening in the ED and identifies seven of the questions used as predictive of likely sex trafficking.

The impact of racism on emergency health care workers

INTRODUCTION

Discrimination based on race is a known source of stress in individuals and is a contributor to poor health outcomes in patients. However, less is known about how the experiences of racism impact the stress levels of emergency health care workers (EHCWs).

OBJECTIVES

The goal of this study was to assess the impact that racism has on the stress of EHCWs.

METHODS

An anonymous electronic cross-sectional survey of EHCWs including attending physicians, resident physicians, advanced practice providers, nurses, and staff at three large metropolitan hospitals was administered in the summer of 2020. The survey evaluated the stress related to systemic racism and the COVID-19 pandemic in addition to the wellness measures utilized to cope with these stressors. The focus of this article is the impact of systemic racism on EHCWs.

RESULTS

Of the 576 eligible participants, the total number of respondents utilized for analysis was 260. Overall, 64% of participants were very concerned about the state of racism in the United States, and 30% reported moderate-high or high stress resulting from racism. When stratified by race, 46% of Black participants reported moderate-high or high stress resulting from racism, compared to 31% of other participants of color and 23% of White participants (p = 0.002).

CONCLUSION

Systemic racism is a significant concern and source of stress for EHCWs. Additional research about systemic racism, its impact on medical providers, and more importantly, active strategies to reduce and ultimately eliminate it in health care is needed.

Self-Reported Use of Personal Protective Equipment among Emergency Department Nurses, Physicians and Advanced Practice Providers during the 2020 COVID-19 Pandemic

Background: Emergency departments (EDs) have seen dramatic surges in patients infected with COVID-19 and are high-risk transmission environments. Knowledge, attitudes and practice regarding personal protective equipment (PPE) among ED health care workers (HCWs) during the COVID-19 pandemic have not been studied, thus this study examines this knowledge gap. Methods: This was a cross-sectional survey of 308 HCWs in two urban EDs in Atlanta, Georgia in April and May of 2020. Results: We surveyed 308 HCWs; 137 responded (44% response rate). All HCWs reported adequate knowledge and 96% reported compliance with PPE guidelines. Reported sources of PPE information: 56.7% charge nurse, 67.3% the institutional COVID-19 website. Frequency of training was positively associated with understanding how to protect themselves and patients (OR = 1.7, 95% CI: 1.0–2.9). Conclusions: Few HCWs are willing to care for patients without PPE, and therefore we should aim for resiliency in the PPE supply chain. EDs should consider multiple communication strategies, including a website with concise information and enhanced training for key personnel, particularly the charge nurse. Attention to frequency in HCW training may be key to improve confidence in protecting themselves and patients. Findings can be leveraged by EDs to implement effective PPE training.

The airway as a route of sensitization to peanut: An update to the dual allergen exposure hypothesis

Food allergies have increased at an alarming rate over the past 2 decades, indicating that environmental factors are driving disease progression. It has been postulated that sensitization to foods, in particular, peanut, occurs through impaired skin. Peanut allergens have been quantified in household dust and may be the culprit source. Indeed, T_H2 cell-skewing innate cytokines can be driven by application of food antigens on both intact and impaired skin of mice, resulting in antigen-specific IgE production and anaphylaxis following allergen exposure. However, allergy induction through the skin can be prevented by induction of oral tolerance before skin exposure. These observations led to the dual allergen exposure hypothesis, according to which oral exposure to food antigens leads to tolerance and antigen exposure on impaired skin leads to allergy. Here, we propose the airway as an alternative route of sensitization in the dual allergen exposure hypothesis that leads to food allergy. Specifically, we will provide evidence from mouse models and human cell-based studies that together implicate the airway as a plausible route of sensitization.

Fecal IgA, Antigen Absorption, and Gut Microbiome Composition Are Associated With Food Antigen Sensitization in Genetically Susceptible Mice

Food allergy is a potentially fatal disease affecting 8% of children and has become increasingly common in the past two decades. Despite the prevalence and severe nature of the disease, the mechanisms underlying sensitization remain to be further elucidated. The Collaborative Cross is a genetically diverse panel of inbred mice that were specifically developed to study the influence of genetics on complex diseases. Using this panel of mouse strains, we previously demonstrated CC027/GeniUnc mice, but not C3H/HeJ mice, develop peanut allergy after oral exposure to peanut in the absence of a Th2-skewing adjuvant. Here, we investigated factors associated with sensitization in CC027/GeniUnc mice following oral exposure to peanut, walnut, milk, or egg. CC027/GeniUnc mice mounted antigen-specific IgE responses to peanut, walnut and egg, but not milk, while C3H/HeJ mice were not sensitized to any antigen. Naïve CC027/GeniUnc mice had markedly lower total fecal IgA compared to C3H/HeJ, which was accompanied by stark differences in gut microbiome composition. Sensitized CC027/GeniUnc mice had significantly fewer CD3+ T cells but higher numbers of CXCR5+ B cells and T follicular helper cells in the mesenteric lymph nodes compared to C3H/HeJ mice, which is consistent with their relative immunoglobulin production. After oral challenge to the corresponding food, peanut- and walnut-sensitized CC027/GeniUnc mice experienced anaphylaxis, whereas mice exposed to milk and egg did not. Ara h 2 was detected in serum collected post-challenge from peanut-sensitized mice, indicating increased absorption of this allergen, while Bos d 5 and Gal d 2 were not detected in mice exposed to milk and egg, respectively. Machine learning on the change in gut microbiome composition as a result of food protein exposure identified a unique signature in CC027/GeniUnc mice that experienced anaphylaxis, including the depletion of Akkermansia. Overall, these results demonstrate several factors associated with enteral sensitization in CC027/GeniUnc mice, including diminished total fecal IgA, increased allergen absorption and altered gut microbiome composition. Furthermore, peanuts and tree nuts may have inherent properties distinct from milk and eggs that contribute to allergy.

Poisonings due to storage in a secondary container reported to the National Poison Data System, 2007-2017

BACKGROUND

Transfer of xenobiotics from their original container to an unlabeled or secondary container is a well-identified risk factor for poisoning. Nonetheless, recent large-scale data on the practice are unavailable. The objective of this study is to describe the incidence and features of poisonings in the United States due to xenobiotics stored in a secondary container.

METHODS

This was a retrospective review of the National Poison Data System (NPDS) from 2007 to 2017. Non-suicidal exposures associated with the scenario "container transfer involved (product transferred from original container to unlabeled container, incorrectly labeled container, or food container for use or storage and patient accessed product from second container)" were included.

RESULTS

Forty-five thousand five hundred and twelve cases were included. The median age of subjects was 30 years (interquartile range: 6-53); 52% were female. Cleaning products (38.2%), disinfectants (17.3%), and hydrocarbons (5.0%) were the most common xenobiotics reported. The annual incidence of cases increased over the study period. There were 9369 (20.6%) ED visits and 1856 (4.1%) hospital admissions. Most cases (72%) were deemed nontoxic or resulted in no effects; 4.4% resulted in serious outcomes (moderate effects, major effects, or death), including 23 deaths. Morbidity was highest for pesticides, prescription medications, and herbicides, with 10.3%, 9.8%, and 7.6% of cases resulting in serious outcomes, respectively. Hydrofluoric acid and herbicides were associated with the most deaths (13/23 [57%]).

CONCLUSIONS

Transfer of xenobiotics to a secondary container is a scenario increasingly reported to U.S. poison centers. Although most exposures do not result in significant toxicity, ED visits are common and substantial morbidity can occur. This represents an opportunity for public health intervention to curb the practice.

The External Exposome and Food Allergy

PURPOSE OF REVIEW

The recent increase in childhood food allergy prevalence strongly suggests that environmental exposures are contributing to food allergy development. This review summarizes current knowledge about the role of the external exposome in food allergy.

RECENT FINDINGS

There is growing evidence that environmental exposure to food antigens in house dust through non-oral routes contributes to food sensitization and allergy. Co-exposure to environmental adjuvants in house dust, such as microbial products and fungal allergens, may also facilitate allergic sensitization. While a high-microbe environment is associated with decreased atopy, studies are mixed on whether endotoxin exposure protects against food sensitization. Several chemicals and air pollutants have been associated with food sensitization, but their role in food allergy remains understudied. Children are exposed to numerous environmental agents that can influence food allergy risk. Further studies are needed to identify the key early-life exposures that promote or inhibit food allergy development.

Indoor dust acts as an adjuvant to promote sensitization to peanut through the airway

BACKGROUND

There is growing evidence that environmental peanut exposure through non-oral routes, including the skin and respiratory tract, can result in peanut sensitization. Environmental adjuvants in indoor dust can promote sensitization to inhaled antigens, but whether they contribute to peanut allergy development is unclear.

OBJECTIVE

We investigated whether indoor dust promotes airway sensitization to peanut and peanut allergy development in mice.

METHODS

Female and male C57BL/6J mice were exposed via the airways to peanut, indoor dust extract, or both for 2 weeks. Mice were then challenged with peanut and assessed for anaphylaxis. Peanut-specific immunoglobulins, peanut uptake by lung conventional dendritic cells (cDCs), lung innate cytokines, and T cell differentiation in lung-draining lymph nodes were quantified. Innate cytokine production by primary human bronchial epithelial cells exposed to indoor dust was also determined.

RESULTS

Inhalational exposure to low levels of peanut in combination with indoor dust, but neither alone, resulted in production of peanut-specific IgE and development of anaphylaxis upon peanut challenge. Indoor dust triggered production of innate cytokines in murine lungs and in primary human bronchial epithelial cells. Additionally, inhaled indoor dust stimulated maturation and migration of peanut-laden lung type 1 cDCs to draining lymph nodes. Inhalational exposure to peanut and indoor dust induced peanut-specific T helper 2 cell differentiation and accumulation of T follicular helper cells in draining lymph nodes, which were associated with increased B cell numbers and peanut-specific immunoglobulin production.

CONCLUSIONS & CLINICAL RELEVANCE

Indoor dust promotes airway sensitization to peanut and development of peanut allergy in mice. Our findings suggest that environmental adjuvants in indoor dust may be determinants of peanut allergy development in children.

Walnut antigens can trigger autoantibody development in patients with pemphigus vulgaris through a "hit-and-run" mechanism

BACKGROUND

Environmental factors, as well as genetic predisposition, are known to be critical for the development of autoimmunity. However, the environmental agents that trigger autoimmune responses have remained elusive. One possible explanation is the "hit-and-run" mechanism in which the inciting antigens that initiate autoimmune responses are not present at the time of overt autoimmune disease.

OBJECTIVE

After our previous findings that some allergens can incite autoimmune responses, we investigated the potential role of environmental allergens in triggering autoantibody development in patients with an autoimmune skin disease, pemphigus vulgaris (PV).

METHODS

Revertant/germline mAbs (with mutations on variable regions of heavy and light chains reverted to germline forms) of 8 anti-desmoglein (Dsg) 3 pathogenic mAbs from patients with PV were tested for reactivity against a panel of possible allergens, including insects, pollens, epithelia, fungi, and food antigens.

RESULTS

All the PV germline mAbs were reactive to antigens from walnut, including the well-known allergen Jug r 2 and an uncharacterized 85-kDa protein component. Sera from patients with PV contained significantly greater levels of anti-Dsg3 autoantibodies than walnut-specific antibodies, suggesting that the autoreactive B-cell response in patients with PV might be initially triggered by walnut antigens but is subsequently driven by Dsg3.

CONCLUSION

Our findings suggest that walnut antigens/allergens can initiate autoantibody development in patients with PV through a "hit-and-run" mechanism. The revertant/germline mAb approach might provide a paradigm for the etiological study of other allergic and autoimmune diseases.

Neuropilin-2 regulates airway inflammatory responses to inhaled lipopolysaccharide

Neuropilins are multifunctional receptors that play important roles in immune regulation. Neuropilin-2 (NRP2) is expressed in the lungs, but whether it regulates airway immune responses is unknown. Here, we report that Nrp2 is weakly expressed by alveolar macrophages (AMs) in the steady state but is dramatically upregulated following in vivo lipopolysaccharide (LPS) inhalation. Ex vivo treatment of human AMs with LPS also increased NRP2 mRNA expression and cell-surface display of NRP2 protein. LPS-induced Nrp2 expression in AMs was dependent upon the myeloid differentiation primary response 88 signaling pathway and the transcription factor NF-κB. In addition to upregulating display of NRP2 on the cell membrane, inhaled LPS also triggered AMs to release soluble NRP2 into the airways. Finally, myeloid-specific ablation of NRP2 resulted in increased expression of the chemokine (C-C motif) ligand 2 ( Ccl2) in the lungs and prolonged leukocyte infiltration in the airways following LPS inhalation. These findings suggest that NRP2 expression by AMs regulates LPS-induced inflammatory cell recruitment to the airways and reveal a novel role for NRP2 during innate immune responses in the lungs.

Metabolite Profiling Reveals the Glutathione Biosynthetic Pathway as a Therapeutic Target in Triple-Negative Breast Cancer

Cancer cells can exhibit altered dependency on specific metabolic pathways and targeting these dependencies is a promising therapeutic strategy. Triple-negative breast cancer (TNBC) is an aggressive and genomically heterogeneous subset of breast cancer that is resistant to existing targeted therapies. To identify metabolic pathway dependencies in TNBC, we first conducted mass spectrometry-based metabolomics of TNBC and control cells. Relative levels of intracellular metabolites distinguished TNBC from nontransformed breast epithelia and revealed two metabolic subtypes within TNBC that correlate with markers of basal-like versus non-basal-like status. Among the distinguishing metabolites, levels of the cellular redox buffer glutathione were lower in TNBC cell lines compared to controls and markedly lower in non-basal-like TNBC. Significantly, these cell lines showed enhanced sensitivity to pharmacologic inhibition of glutathione biosynthesis that was rescued by N-acetylcysteine, demonstrating a dependence on glutathione production to suppress ROS and support tumor cell survival. Consistent with this, patients whose tumors express elevated levels of γ-glutamylcysteine ligase, the rate-limiting enzyme in glutathione biosynthesis, had significantly poorer survival. We find, further, that agents that limit the availability of glutathione precursors enhance both glutathione depletion and TNBC cell killing by γ-glutamylcysteine ligase inhibitors in vitro Importantly, we demonstrate the ability to this approach to suppress glutathione levels and TNBC xenograft growth in vivo Overall, these findings support the potential of targeting the glutathione biosynthetic pathway as a therapeutic strategy in TNBC and identify the non-basal-like subset as most likely to respond. Mol Cancer Ther; 17(1); 264-75. ©2017 AACR.

TNF is required for TLR ligand-mediated but not protease-mediated allergic airway inflammation

Asthma is associated with exposure to a wide variety of allergens and adjuvants. The extent to which overlap exists between the cellular and molecular mechanisms triggered by these various agents is poorly understood, but it might explain the differential responsiveness of patients to specific therapies. In particular, it is unclear why some, but not all, patients benefit from blockade of TNF. Here, we characterized signaling pathways triggered by distinct types of adjuvants during allergic sensitization. Mice sensitized to an innocuous protein using TLR ligands or house dust extracts as adjuvants developed mixed eosinophilic and neutrophilic airway inflammation and airway hyperresponsiveness (AHR) following allergen challenge, whereas mice sensitized using proteases as adjuvants developed predominantly eosinophilic inflammation and AHR. TLR ligands, but not proteases, induced TNF during allergic sensitization. TNF signaled through airway epithelial cells to reprogram them and promote Th2, but not Th17, development in lymph nodes. TNF was also required during the allergen challenge phase for neutrophilic and eosinophilic inflammation. In contrast, TNF was dispensable for allergic airway disease in a protease-mediated model of asthma. These findings might help to explain why TNF blockade improves lung function in only some patients with asthma.

Inhaled house dust programs pulmonary dendritic cells to promote type 2 T-cell responses by an indirect mechanism

The induction of allergen-specific T helper 2 (Th2) cells by lung dendritic cells (DCs) is a critical step in allergic asthma development. Airway delivery of purified allergens or microbial products can promote Th2 priming by lung DCs, but how environmentally relevant quantities and combinations of these factors affect lung DC function is unclear. Here, we investigated the ability of house dust extract (HDE), which contains a mixture of environmental adjuvants, to prime Th2 responses against an innocuous inhaled antigen. Inhalational exposure to HDE conditioned lung conventional DCs, but not monocyte-derived DCs, to induce antigen-specific Th2 differentiation. Conditioning of DCs by HDE was independent of Toll-like receptor 4 signaling, indicating that environmental endotoxin is dispensable for programming DCs to induce Th2 responses. DCs directly treated with HDE underwent maturation but were poor stimulators of Th2 differentiation. In contrast, DCs treated with bronchoalveolar lavage fluid (BALF) from HDE-exposed mice induced robust Th2 differentiation. DC conditioning by BALF was independent of the proallergic cytokines IL-25, IL-33, and thymic stromal lymphopoietin. BALF treatment of DCs resulted in upregulation of CD80 but low expression of CD40, CD86, and IL-12p40, which was associated with Th2 induction. These findings support a model whereby environmental adjuvants in house dust indirectly program DCs to prime Th2 responses by triggering the release of endogenous soluble factor(s) by airway cells. Identifying these factors could lead to novel therapeutic targets for allergic asthma.

Complement receptor C5aR1/CD88 and dipeptidyl peptidase-4/CD26 define distinct hematopoietic lineages of dendritic cells

Differential display of the integrins CD103 and CD11b are widely used to distinguish two major dendritic cell (DC) subsets in nonlymphoid tissues. CD103(+) DCs arise from FLT3-dependent DC precursors (preDCs), whereas CD11b(hi) DCs can arise either from preDCs or FLT3-independent monocytes. Functional characterization of these two lineages of CD11b(hi) DCs has been hindered by the lack of a widely applicable method to distinguish between them. We performed gene expression analysis of fractionated lung DCs from C57BL/6 mice and found that monocyte-derived DCs (moDCs), including CD11b(hi)Ly-6C(lo) tissue-resident and CD11b(hi)Ly-6C(hi) inflammatory moDCs, express the complement 5a receptor 1/CD88, whereas preDC-derived conventional DCs (cDCs), including CD103(+) and CD11b(hi) cDCs, express dipeptidyl peptidase-4/CD26. Flow cytometric analysis of multiple organs, including the kidney, liver, lung, lymph nodes, small intestine, and spleen, confirmed that reciprocal display of CD88 and CD26 can reliably distinguish FLT3-independent moDCs from FLT3-dependent cDCs in C57BL/6 mice. Similar results were obtained when DCs from BALB/c mice were analyzed. Using this novel approach to study DCs in mediastinal lymph nodes, we observed that most blood-derived lymph node-resident DCs, as well as tissue-derived migratory DCs, are cDCs. Furthermore, cDCs, but not moDCs, stimulated naive T cell proliferation. We anticipate that the use of Abs against CD88 and CD26 to distinguish moDCs and cDCs in multiple organs and mouse strains will facilitate studies aimed at assigning specific functions to distinct DC lineages in immune responses.

Epigenetic control of Ccr7 expression in distinct lineages of lung dendritic cells

Adaptive immune responses to inhaled allergens are induced following CCR7-dependent migration of precursor of dendritic cell (pre-DC)-derived conventional DCs (cDCs) from the lung to regional lymph nodes. However, monocyte-derived (moDCs) in the lung express very low levels of Ccr7 and consequently do not migrate efficiently to LN. To investigate the molecular mechanisms that underlie this dichotomy, we studied epigenetic modifications at the Ccr7 locus of murine cDCs and moDCs. When expanded from bone marrow precursors, moDCs were enriched at the Ccr7 locus for trimethylation of histone 3 lysine 27 (H3K27me3), a modification associated with transcriptional repression. Similarly, moDCs prepared from the lung also displayed increased levels of H3K27me3 at the Ccr7 promoter compared with migratory cDCs from that organ. Analysis of DC progenitors revealed that epigenetic modification of Ccr7 does not occur early during DC lineage commitment because monocytes and pre-DCs both had low levels of Ccr7-associated H3K27me3. Rather, Ccr7 is gradually silenced during the differentiation of monocytes to moDCs. Thus, epigenetic modifications of the Ccr7 locus control the migration and therefore the function of DCs in vivo. These findings suggest that manipulating epigenetic mechanisms might be a novel approach to control DC migration and thereby improve DC-based vaccines and treat inflammatory diseases of the lung.

Increased immunogenicity of a DNA-launched Venezuelan equine encephalitis virus-based replicon DNA vaccine

A novel genetic vaccine that is based on a Venezuelan equine encephalitis virus (VEE) replicon launched from plasmid DNA is described. The plasmid encodes a VEE replicon under the transcriptional control of the cytomegalovirus immediate-early promoter (VEE DNA). The VEE DNA consistently expressed 3- to 15-fold more green fluorescent protein in vitro than did a conventional DNA vaccine. Furthermore, transfection with the DNA-launched VEE replicon induced apoptosis and type I interferon production. Inoculation of mice with VEE DNA encoding human immunodeficiency virus type 1 gp160 significantly increased humoral responses by several orders of magnitude compared to an equal dose of a conventional DNA vaccine. These increases were also observed at 10- and 100-fold-lower doses of the VEE DNA. Cellular immune responses measured by gamma interferon and interleukin 2 enzyme-linked immunospot assay were significantly higher in mice immunized with the VEE DNA at decreased doses. The immune responses induced by the VEE DNA-encoded antigen, however, were independent of an intact type I interferon signaling pathway. Moreover, the DNA-launched VEE replicon induced an efficient prime to a VEE replicon particle (VRP) boost, increasing humoral and cellular immunity by at least 1 order of magnitude compared to VEE DNA only. Importantly, immunization with VEE DNA, as opposed to VRP, did not induce any anti-VRP neutralizing antibodies. Increased potency of DNA vaccines and reduced vector immunity may ultimately have an impact on the design of vaccination strategies in humans.

Alphaviral vector-transduced dendritic cells are successful therapeutic vaccines against neu-overexpressing tumors in wild-type mice

While dendritic cell (DC) vaccines can protect hosts from tumor challenge, their ability to effectively inhibit the growth of established tumors remains indeterminate. Previously, we have shown that human DCs transduced with Venezuelan equine encephalitis virus replicon particles (VRPs) were potent stimulators of antigen-specific T cells in vitro. Therefore, we investigated the ability of VRP-transduced DCs (VRP-DCs) to induce therapeutic immunity in vivo against tumors overexpressing the neu oncoprotein. Transduction of murine DCs with VRPs resulted in high-level transgene expression, DC maturation and secretion of proinflammatory cytokines. Vaccination with VRP-DCs expressing a truncated neu oncoprotein induced robust neu-specific CD8(+) T cell and anti-neu IgG responses. Furthermore, a single vaccination with VRP-DCs induced the regression of large established tumors in wild-type mice. Interestingly, depletion of CD4(+), but not CD8(+), T cells completely abrogated inhibition of tumor growth following vaccination. Taken together, our results demonstrate that VRP-DC vaccines induce potent immunity against established tumors, and emphasize the importance of the generation of both CD4(+) T cell and B cell responses for efficient tumor inhibition. These findings provide the rationale for future evaluation of VRP-DC vaccines in the clinical setting.

A Novel Viral System for Generating Antigen-Specific T Cells

Dendritic cell (DC)-based vaccines are increasingly used for the treatment of patients with malignancies. Although these vaccines are typically safe, consistent and lasting generation of tumor-specific immunity has been rarely demonstrated. Improved methods for delivering tumor Ags to DCs and approaches for overcoming tolerance or immune suppression to self-Ags are critical for improving immunotherapy. Viral vectors may address both of these issues, as they can be used to deliver intact tumor Ags to DCs, and have been shown to inhibit the suppression mediated by CD4+CD25+ regulatory T cells. We have evaluated the potential use of Venezuelan equine encephalitis virus replicon particles (VRPs) for in vitro Ag delivery to human monocyte-derived DCs. VRPs efficiently transduced immature human DCs in vitro, with approximately 50% of immature DCs expressing a vector-driven Ag at 12 h postinfection. VRP infection of immature DCs was superior to TNF-alpha treatment at inducing phenotypic maturation of DCs, and was comparable to LPS stimulation. Additionally, VRP-infected DC cultures secreted substantial amounts of the proinflammatory cytokines IL-6, TNF-alpha, and IFN-alpha. Finally, DCs transduced with a VRP encoding the influenza matrix protein (FMP) stimulated 50% greater expansion of FMP-specific CD8+ CTL when compared with TNF-alpha-matured DCs pulsed with an HLA-A*0201-restricted FMP peptide. Thus, VRPs can be used to deliver Ags to DCs resulting in potent stimulation of Ag-specific CTL. These findings provide the rationale for future studies evaluating the efficacy of VRP-transduced DCs for tumor immunotherapy.

Direct cytotoxic action of Shiga toxin on human vascular endothelial cells

To help explain a role of the Shiga toxin family in hemorrhagic colitis and hemolytic-uremic syndrome in humans, it has been hypothesized that these toxins cause direct damage to the vascular endothelium. We now report that Shiga toxin purified from Shigella dysenteriae 1 does indeed have a direct cytotoxic effect on vascular endothelial cells in cultures. Human umbilical vein endothelial cells (HUVEC) in confluent monolayers were reduced 50% by 10(-8) M Shiga toxin after a lag period of 48 to 96 h. In comparison, nonconfluent HUVEC were reduced 50% by 10(-10) M Shiga toxin within a 24-h period. These data suggest that dividing endothelial cells are more sensitive to Shiga toxin than are quiescent cells in confluent monolayers. Both confluent and nonconfluent HUVEC specifically bound 125I-Shiga toxin. However, in response to the toxin, rates of incorporation of [3H]leucine into protein were more severely reduced in nonconfluent cells than in confluent cells. Toxin inhibition of protein synthesis preceded detachment of cells from the substratum. The specific binding of 125I-Shiga toxin to human endothelial cells and the cytotoxic response were both toxin dose dependent and neutralized by anti-Shiga toxin antibody. Heat-denatured Shiga toxin was without the cytotoxic effect. In addition, the complete culture system contained less than 0.1 ng of bacterial endotoxin per ml, as measured by the Limulus amoebocyte lysate test.

The mode of action of Shiga toxin on peptide elongation of eukaryotic protein synthesis

The effect of Shiga toxin, from Shigella dysenteriae 1, on the component reactions of peptide elongation were investigated. Enzymic binding of [3H]phenylalanine-tRNA to reticulocyte ribosomes was inhibited by 50% at 7 nM toxin. Elongation factor 1 (eEF-1)-dependent GTPase activity was also inhibited. Both reactions were not restored by addition of excess eEF-1 protein. In contrast, toxin concentrations of 200 nM were required to inhibit by 50% the elongation factor 2 (eEF-2)-dependent translocation of aminoacyl-tRNA on ribosomes. Addition of excess eEF-2 restored translocation activity. The eEF-2-dependent GTPase activity was unaffected at toxin concentrations below 100 nM, and Shiga-toxin concentrations of up to 1,000 nM did not affect either GTP.eEF-2.ribosome complex-formation or peptidyltransferase activity. Thus Shiga toxin closely resembles alpha-sarcin in action, both being primary inhibitors of eEF-1-dependent reactions. In contrast, the 60 S ribosome inactivators ricin and phytolaccin are primary inhibitors of eEF-2-dependent reactions of peptide elongation.

Shiga toxin from Shigella dysenteriae 1 inhibits protein synthesis in reticulocyte lysates by inactivation of aminoacyl-tRNA binding

Inhibition of the peptide elongation cycle of eukaryotic protein synthesis by Shiga toxin from Shigella dysenteriae 1 was examined in toxin-treated reticulocyte lysate mixtures. Peptidyl transferase activity of toxin-treated ribosomes was measured by following the decrease in peptidyl-tRNA concentrations when puromycin was added after incubation with toxin. Concentrations of [3H]leucine-labeled peptidyl-tRNA were measured by extraction with cetyltrimethylammonium bromide. The data suggest that Shiga toxin inhibited aminoacyl-tRNA binding. Toxin-treated ribosomes retained peptidyl transferase activity, and toxin did not block translocation. Furthermore, no inhibition of initiation of protein synthesis could be observed. Finally, Shiga toxin had no detectable nucleolytic effect on polysomal 28S rRNA, nor was hydrolysis of 5.8S or 5S rRNA observed.