A retrospective observational study of mNGS test utilization to examine the role of diagnostic stewardship at two academic medical centers.

Given the cost and unclear clinical impact of metagenomic next-generation sequencing (mNGS), laboratory stewardship may improve utilization. This retrospective observational study examines mNGS results from two academic medical centers employing different stewardship approaches. Eighty mNGS orders [54 cerebrospinal fluid (CSF) and 26 plasma] were identified from 2019 to 2021 at the University of Washington (UW), which requires director-level approval for mNGS orders, and the University of Utah (Utah), which does not restrict ordering. The impact of mNGS results and the relationship to traditional microbiology orders were evaluated. Nineteen percent (10/54) of CSF and 65% (17/26) of plasma studies detected at least one organism. Compared to CSF results, plasma results more frequently identified clinically significant organisms (31% vs 7%) and pathogens not detected by traditional methods (12% vs 0%). Antibiotic management was more frequently impacted by plasma versus CSF results (31% vs 4%). These outcome measures were not statistically different between study sites. The number and cumulative cost of traditional microbiology tests at UW were greater than Utah for CSF mNGS testing (UW: 46 tests, $6,237; Utah: 26 tests, $2,812; P < 0.05) but similar for plasma mNGS (UW: 31 tests, $3,975; Utah: 21 tests, $2,715; P = 0.14). mNGS testing accounted for 30%-50% of the total microbiology costs. Improving the diagnostic performance of mNGS by stewardship remains challenging due to low positivity rates and difficulties assessing clinical impact. From a fiscal perspective, stewardship efforts should focus on reducing testing in low-yield populations given the high costs of mNGS relative to overall microbiology testing expenditures. IMPORTANCE: Metagenomic next-generation sequencing (mNGS) stewardship practices remain poorly standardized. This study aims to provide actionable insights for institutions that seek to reduce the unnecessary usage of mNGS. Importantly, we highlight that clinical impact remains challenging to measure without standardized guidelines, and we provide an actual cost estimate of microbiology expenditures on individuals undergoing mNGS.

Repeat testing of mpox specimens with late CTs improves detection of potential false positive cases.

The mpox pandemic necessitated the rapid development of clinical assays for monkeypox virus detection. While the majority of mpox specimens have high viral loads with corresponding early cycle threshold (CT) values, reports have indicated some specimens with late CT values can represent false positive results. To mitigate this risk, the Centers for Disease Control and Prevention (CDC) published an advisory recommending repeat testing of all specimens with CT values ≥34. However, limited experimental data were available to support this specific cutoff. In this study, we examine whether a more conservative approach in which all specimens with CT values ≥29 are repeated would improve the detection of potential false positive results. Compared to the CDC algorithm, our approach identified an additional 20% (5/25) of potential false positive results. To assess the impact of this cutoff on laboratory workload, we modeled the expected increase in test volume and turnaround time (TAT) relative to the CDC method. Using a lower repeat threshold, test volume increased by 0.7% while mean TAT increased by less than 15 minutes. Overall, a lower threshold than recommended by the CDC for repeating late CT mpox specimens may reduce the number of false positives reported while minimally impacting testing volume and TAT.

Characterization of the Cytopathic Effects of Monkeypox Virus Isolated from Clinical Specimens and Differentiation from Common Viral Exanthems.

While the practice of viral culture has largely been replaced by nucleic acid amplification tests, circumstances still exist in which the availability of viral culture will allow for the diagnosis of infections not included in a provider's differential diagnosis. Here, we examine the cytopathic effects (CPE) and clinical data associated with 18 cases of monkeypox virus (MPXV) isolated from 19 clinical samples submitted for viral culture. During the study period, a total of 3,468 viral cultures were performed with herpes simplex virus (HSV) most commonly isolated (646/3,468; 18.6%), followed by MPXV (19/3,468; 0.6%) and varicella-zoster virus (VZV) (12/3,468; 0.4%). Most MPXV-positive samples were obtained from males (14/19) and taken from genital (7/19) or rectal lesions (5/19). Cycle threshold values of tested samples ranged from 15.3 to 29.0. Growth of MPXV in cell culture was rapid, yielding detectable CPE at a median of 2 days (range: 1 to 4) often with >50% of the monolayer affected in RMK, BGM, A549, and MRC-5 cell lines. As clinical features of MPXV, HSV, and VZV lesions may overlap, CPE patterns were compared between viruses. HSV CPE developed in a similar time frame (median: 2 days, range: 1 to 7) but was more often negative in RMK cells relative to MPXV. VZV grew more slowly (median: 9 days, range: 5 to 11) and demonstrated CPE affecting ≤25% of cell monolayers when positive. Viral culture remains an important tool for the detection of rare or emerging viral pathogens, particularly when high viral load specimens are easily obtained.

Clinical Performance and Trends during the First Two Months of Monkeypox Virus PCR Testing at Two United States Reference Labs.

Recently, a sustained human-to-human outbreak of monkeypox virus (MPXV), a member of the Orthopoxvirus genus, which includes the etiologic agent of smallpox, has been documented in multiple nonendemic countries, including the United States. Prior to June 2022, testing in the United States was limited to public health labs and the Centers for Disease Control and Prevention. Following recognition of the scope of the outbreak, testing for MPXV has expanded into clinical laboratories. Here, we examine epidemiological characteristics, specimen collection practices, and cycle threshold (Ct) values for 10,019 MPXV PCR tests performed at two reference laboratories. Results from both laboratories support public health data showing a high positivity rate in men (>30%) and those ages 30 to 49 (25 to 35%). The overall positivity rate decreased during the study period but remains elevated (~20%). There was a significant difference in Ct values between laboratories (ARUP 23.9 versus UW 25.4) and collection method (22.8 for dry swab versus 24.4 for VTM), likely reflecting slight differences in specimen processing. When multiple specimens were collected for a single individual, the overall result concordance rate was greater than 95%, with less than 1.5% of individuals receiving three or more tests having a single positive result. Compared to the overall positive cohort, individuals with three or more swabs collected and a single positive result had significantly higher Ct values (22.9 versus 35.0). Intriguingly, individuals aged 50 to 59 years old had a significantly different viral load distribution than those found in younger age groups, potentially associated with prior vaccinia virus vaccination. These results provide an early snapshot of testing in the United States during the monkeypox virus outbreak and support restricting the number of swabs collected per individual.

In Vivo Generation of BK and JC Polyomavirus Defective Viral Genomes in Human Urine Samples Associated with Higher Viral Loads.

Defective viral genomes (DVGs) are parasitic viral sequences containing point mutations, deletions, or duplications that might interfere with replication. DVGs are often associated with viral passage at high multiplicities of infection in culture systems but have been increasingly reported in clinical specimens. To date however, only RNA viruses have been shown to contain DVGs in clinical specimens. Here, using direct deep sequencing with multiple library preparation strategies and confirmatory digital droplet PCR (ddPCR) of urine samples taken from immunosuppressed individuals, we show that clinical BK polyomavirus (BKPyV) and JC polyomavirus (JCPyV) strains contain widespread genomic rearrangements across multiple loci that likely interfere with viral replication. BKPyV DVGs were derived from BKPyV genotypes Ia, Ib-1, and Ic. The presence of DVGs was associated with specimens containing higher viral loads but never reached clonality, consistent with a model of parasitized replication. These DVGs persisted during clinical infection as evidenced in two separate pairs of samples containing BK virus collected from the same individual up to 302 days apart. In a separate individual, we observed the generation of DVGs after a 57.5-fold increase in viral load. In summary, by extending the presence of DVGs in clinical specimens to DNA viruses, we demonstrate the ubiquity of DVGs in clinical virology.IMPORTANCE Defective viral genomes (DVGs) can have a significant impact on the production of infectious virus particles. DVGs have only been identified in cultured viruses passaged at high multiplicities of infection and RNA viruses collected from clinical specimens; no DNA virus in the wild has been shown to contain DVGs. Here, we identified BK and JC polyomavirus DVGs in clinical urine specimens and demonstrated that these DVGs are more frequently identified in samples with higher viral loads. The strains containing DVGs had rearrangements throughout their genomes, with the majority affecting genes required for viral replication. Longitudinal analysis showed that these DVGs can persist during an infection but do not reach clonality within the chronically infected host. Our identification of polyomavirus DVGs suggests that these parasitic sequences exist across the many classes of viruses capable of causing human disease.

Histopathology and ultrastructural findings of fatal COVID-19 infections in Washington State: a case series.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of an ongoing pandemic, with increasing deaths worldwide. To date, documentation of the histopathological features in fatal cases of the disease caused by SARS-CoV-2 (COVID-19) has been scarce due to sparse autopsy performance and incomplete organ sampling. We aimed to provide a clinicopathological report of severe COVID-19 cases by documenting histopathological changes and evidence of SARS-CoV-2 tissue tropism. METHODS: In this case series, patients with a positive antemortem or post-mortem SARS-CoV-2 result were considered eligible for enrolment. Post-mortem examinations were done on 14 people who died with COVID-19 at the King County Medical Examiner's Office (Seattle, WA, USA) and Snohomish County Medical Examiner's Office (Everett, WA, USA) in negative-pressure isolation suites during February and March, 2020. Clinical and laboratory data were reviewed. Tissue examination was done by light microscopy, immunohistochemistry, electron microscopy, and quantitative RT-PCR. FINDINGS: The median age of our cohort was 73·5 years (range 42-84; IQR 67·5-77·25). All patients had clinically significant comorbidities, the most common being hypertension, chronic kidney disease, obstructive sleep apnoea, and metabolic disease including diabetes and obesity. The major pulmonary finding was diffuse alveolar damage in the acute or organising phases, with five patients showing focal pulmonary microthrombi. Coronavirus-like particles were detected in the respiratory system, kidney, and gastrointestinal tract. Lymphocytic myocarditis was observed in one patient with viral RNA detected in the tissue. INTERPRETATION: The primary pathology observed in our cohort was diffuse alveolar damage, with virus located in the pneumocytes and tracheal epithelium. Microthrombi, where observed, were scarce and endotheliitis was not identified. Although other non-pulmonary organs showed susceptibility to infection, their contribution to the pathogenesis of SARS-CoV-2 infection requires further examination. FUNDING: None.

Anti-SARS-CoV-2 Antibody Levels Measured by the AdviseDx SARS-CoV-2 Assay Are Concordant with Previously Available Serologic Assays but Are Not Fully Predictive of Sterilizing Immunity.

With the availability of widespread SARS-CoV-2 vaccination, high-throughput quantitative anti-spike protein serological testing will likely become increasingly important. Here, we investigated the performance characteristics of the recently FDA-authorized semiquantitative anti-spike protein AdviseDx SARS-CoV-2 IgG II assay compared to the FDA-authorized anti-nucleocapsid protein Abbott Architect SARS-CoV-2 IgG, Roche Elecsys anti-SARS-CoV-2-S, EuroImmun anti-SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA), and GenScript surrogate virus neutralization assays and examined the humoral response associated with vaccination, natural protection, and vaccine breakthrough infection. The AdviseDx assay had a clinical sensitivity at 14 days after symptom onset or 10 days after PCR detection of 95.6% (65/68; 95% confidence interval [CI], 87.8 to 98.8%), with two discrepant individuals seroconverting shortly thereafter. The AdviseDx assay demonstrated 100% positive percent agreement with the four other assays examined using the same symptom onset or PCR detection cutoffs. Using a recently available WHO international standard for anti-SARS-CoV-2 antibody, we provide assay unit conversion factors to international units for each of the assays examined. We performed a longitudinal survey of healthy vaccinated individuals, finding that median AdviseDx immunoglobulin levels peaked 7 weeks after first vaccine dose at approximately 4,000 IU/ml. Intriguingly, among the five assays examined, there was no significant difference in antigen binding level or neutralizing activity between two seropositive patients protected against SARS-CoV-2 infection in a previously described fishing vessel outbreak and five health care workers who experienced vaccine breakthrough of SARS-CoV-2 infection, all with variants of concern. These findings suggest that protection against SARS-CoV-2 infection cannot currently be predicted exclusively using in vitro antibody assays against wild-type SARS-CoV-2 spike. Further work is required to establish protective correlates for SARS-CoV-2 infection.

Emerging respiratory infections: The infectious disease pathology of SARS, MERS, pandemic influenza, and Legionella.

Lower respiratory infections remain one of the top global causes of death and the emergence of new diseases continues to be a concern. In the first two decades of the 21st century, we have born witness to the emergence of newly recognized coronaviruses that have rapidly spread around the globe, including severe acute respiratory syndrome virus (SARS) and Middle Eastern respiratory syndrome virus (MERS). We have also experienced the emergence of a novel H1N1 pandemic influenza strain in 2009 that caused substantial morbidity and mortality around the world and has transitioned into a seasonal strain. Although we perhaps most frequently think of viruses when discussing emerging respiratory infections, bacteria have not been left out of the mix, as we have witnessed an increase in the number of infections from Legionella spp. since the organisms' initial discovery in 1976. Here, we explore the basic epidemiology, clinical presentation, histopathology, and clinical laboratory diagnosis of these four pathogens and emphasize themes in humans' evolving relationship with our natural environment that have contributed to the infectious burden. Histology alone is rarely diagnostic for these infections, but has been crucial to bettering our understanding of these diseases. Together, we rely on the diagnostic acumen of pathologists to identify the clinicopathologic features that raise the suspicion of these diseases and lead to the early control of the spread in our populations.

Opportunities and challenges for the U.S. laboratory response to highly pathogenic avian influenza A(H5N1).

On March 25, 2024 an outbreak of highly pathogenic avian influenza (HPAI) A H5N1 was identified in dairy cows across multiple farms in the United States. Zoonotic cases originating in individuals with close contact to infected herds and poultry flocks have been subsequently identified. Spillover events such as this raise the specter of recent pandemics including COVID-19 and Mpox and may lead clinical laboratories to assess their capacity for diagnosis of HPAI H5N1. In this review, we detail the origins of the H5N1 clade 2.3.4.4b outbreak as well as the existing capacity to identify HPAI H5N1 as influenza A virus by commercially available assays. Furthermore, we highlight the absence of commercially available influenza A H5 subtyping assays and limitations associated with the current 510(k)-cleared assay. This outbreak also serves as an early opportunity to assess the new and unknown regulatory challenges faced by laboratory-developed tests in light of the FDA's final rule on in vitro diagnostic devices. National agencies along with public health and clinical laboratories all serve an essential role in the response to HPAI H5N1. To most effectively utilize each group's strength requires open communication and willingness to embrace novel approaches.

NADPH oxidase-dependent and -independent mechanisms of reported inhibitors of reactive oxygen generation.

NADPH oxidase isoform-2 (NOX2) generates reactive oxygen species (ROS) that contribute to neurodegenerative and cardiovascular pathologies. However, validation of NOX2 as a pharmacotherapeutic target has been hampered by a lack of mechanistically-defined inhibitors. Using cellular and biochemical assays, we explored previously reported inhibitors of ROS production (perhexiline, suramin, VAS2870 and two Shionogi patent compounds) as direct NOX2 inhibitors. All but suramin, which presumably lacks cell penetrance, inhibit cellular ROS production. However, only perhexiline and suramin inhibit biochemical NOX2 activity. Indeed, our data suggest that NOX2 inhibition by perhexiline may contribute significantly to its demonstrated cardioprotective effects. Inhibition of protein kinase CßII explains the cellular activity of the Shionogi compounds, whereas VAS2870 inhibits by an as-yet unidentified mechanism unrelated to direct NOX2 function or subunit assembly. These data delineate the mechanisms of action of these compounds and highlight their strengths and limitations for use in future target validation studies.

Review of the Clinical Presentation, Pathology, Diagnosis, and Treatment of Leishmaniasis.

Leishmaniasis is a vector-borne infection caused by kinetoplastid protozoans in the genera Leishmania and Endotrypanum. The disease occurs worldwide in the tropics and subtropics and can be particularly burdensome in resource-limited settings. Diseases caused by leishmaniasis range in severity from mild cutaneous lesions to life-threatening visceral and disfiguring mucocutaneous illnesses. Rapid and accurate diagnosis is needed to ensure proper clinical management of patients afflicted with this disease. Complicating matters of diagnosis and treatment are the diversity of species within these 2 genera and the variable specificity of diagnostic assays. This mini-review provides laboratory professionals with an overview of Leishmania epidemiology, biology, pathogenesis, clinical presentations, and treatments with additional emphasis placed on the nuances involved in diagnosis.

Clinical testing of pediatric mpox specimens: Unique features and challenges in a low prevalence population.

BACKGROUND: Pediatric mpox cases comprise less than 0.3% of the total cases reported in the United States during the global 2022 outbreak. As a result, relatively little is known about the epidemiology or performance characteristics of clinical testing in this group. METHODS: We retrospectively extracted and analyzed results for pediatric mpox specimens tested at a national reference laboratory from July to December 2022. RESULTS: During our study period 13.4% (2,063/15,385) of specimens were from individuals <18 years of age. The positivity rate of pediatric specimens was significantly lower than in adults (1.3% vs 22.3%). The pediatric cohort also consisted of a higher percentage of females (42.7% vs 31.0%) and lower percentage of specimens from genital sources (9.0% vs 19.7%) as compared to adults. In children, specimens were most frequently collected from 1-year-olds (10.1%) and least frequently from 11-year-olds (3.5%). Positivity rates were disproportionately elevated in the less than 1-year-old and 17-year-old age groups (7.8% and 6.4%, respectively). Ct values of positive cases were not statistically different between pediatric and adult cohorts (25.2 vs 22.2, p>0.05). When all pediatric cases with an initial positive mpox result were examined, 5/26 were classified as inconclusive and 2/26 were determined to be false positives. The positive predictive value of monkeypox virus detection was 90.5% (95% CI: 70.4-97.4%) in children. CONCLUSION: These results highlight important differences between pediatric and adult mpox populations and reinforce the need for clinical correlation when reporting positive results from a low prevalence population.

Pulmonary Co-Infections Detected Premortem Underestimate Postmortem Findings in a COVID-19 Autopsy Case Series.

Bacterial and fungal co-infections are reported complications of coronavirus disease 2019 (COVID-19) in critically ill patients but may go unrecognized premortem due to diagnostic limitations. We compared the premortem with the postmortem detection of pulmonary co-infections in 55 fatal COVID-19 cases from March 2020 to March 2021. The concordance in the premortem versus the postmortem diagnoses and the pathogen identification were evaluated. Premortem pulmonary co-infections were extracted from medical charts while applying standard diagnostic definitions. Postmortem co-infection was defined by compatible lung histopathology with or without the detection of an organism in tissue by bacterial or fungal staining, or polymerase chain reaction (PCR) with broad-range bacterial and fungal primers. Pulmonary co-infection was detected premortem in significantly fewer cases (15/55, 27%) than were detected postmortem (36/55, 65%; p < 0.0001). Among cases in which co-infection was detected postmortem by histopathology, an organism was identified in 27/36 (75%) of cases. Pseudomonas, Enterobacterales, and Staphylococcus aureus were the most frequently identified bacteria both premortem and postmortem. Invasive pulmonary fungal infection was detected in five cases postmortem, but in no cases premortem. According to the univariate analyses, the patients with undiagnosed pulmonary co-infection had significantly shorter hospital (p = 0.0012) and intensive care unit (p = 0.0006) stays and significantly fewer extra-pulmonary infections (p = 0.0021). Bacterial and fungal pulmonary co-infection are under-recognized complications in critically ill patients with COVID-19.

IL-13 is a driver of COVID-19 severity.

Immune dysregulation is characteristic of the more severe stages of SARS-CoV-2 infection. Understanding the mechanisms by which the immune system contributes to COVID-19 severity may open new avenues to treatment. Here, we report that elevated IL-13 was associated with the need for mechanical ventilation in 2 independent patient cohorts. In addition, patients who acquired COVID-19 while prescribed Dupilumab, a mAb that blocks IL-13 and IL-4 signaling, had less severe disease. In SARS-CoV-2-infected mice, IL-13 neutralization reduced death and disease severity without affecting viral load, demonstrating an immunopathogenic role for this cytokine. Following anti-IL-13 treatment in infected mice, hyaluronan synthase 1 (Has1) was the most downregulated gene, and accumulation of the hyaluronan (HA) polysaccharide was decreased in the lung. In patients with COVID-19, HA was increased in the lungs and plasma. Blockade of the HA receptor, CD44, reduced mortality in infected mice, supporting the importance of HA as a pathogenic mediator. Finally, HA was directly induced in the lungs of mice by administration of IL-13, indicating a new role for IL-13 in lung disease. Understanding the role of IL-13 and HA has important implications for therapy of COVID-19 and, potentially, other pulmonary diseases. IL-13 levels were elevated in patients with severe COVID-19. In a mouse model of the disease, IL-13 neutralization reduced the disease and decreased lung HA deposition. Administration of IL-13-induced HA in the lung. Blockade of the HA receptor CD44 prevented mortality, highlighting a potentially novel mechanism for IL-13-mediated HA synthesis in pulmonary pathology.

Regulation of the ADMA-DDAH system in endothelial cells: a novel mechanism for the sterol response element binding proteins, SREBP1c and -2.

Asymmetric dimethylarginine (ADMA) has been implicated in the progression of cardiovascular disease as an endogenous inhibitor of nitric oxide synthase. The regulation of dimethylarginine dimethylaminohydrolase (DDAH), the enzyme responsible for metabolizing ADMA, is poorly understood. The transcription factor sterol response element binding protein (SREBP) is activated by statins via a reduction of membrane cholesterol content. Because the promoters of both DDAH1 and DDAH2 isoforms contain sterol response elements, we tested the hypothesis that simvastatin regulates DDAH1 and DDAH2 transcription via SREBP. In cultured endothelial cells, simvastatin increased DDAH1 mRNA expression compared with vehicle. In an ADMA loading experiment, simvastatin treatment resulted in a decrease in ADMA content, an indication of increased DDAH activity. The knockdown of SREBP1c protein led to an increase in DDAH1 mRNA expression and activity, whereas the knockdown of SREBP2 led to a decrease in DDAH1 mRNA expression. The role of SREBP2 in the activation of the DDAH1 was supported by chromatin immunoprecipitation studies demonstrating increased binding of SREBP2 to the DDAH1 promoter upon simvastatin stimulation. These data indicate that SREBP1c might act as a repressor and SREBP2 as an activator of DDAH transcription and activity. This study describes a novel mechanism of reciprocal regulation by the SREBP family members of the DDAH-ADMA system, which represents a potential link between cellular cholesterol content and endothelial dysfunction observed in cardiovascular disease.

High-resolution profiling of human cytomegalovirus cell-free DNA in human plasma highlights its exceptionally fragmented nature.

Human cytomegalovirus (CMV) infections comprise a leading cause of newborn impairments worldwide and are pervasive concerns among the immunocompromised. Quantification of CMV viral loads is increasingly used to guide definitions of CMV disease but standardization of CMV quantitation remains problematic, mostly due to differences in qPCR amplicon sizes between clinical laboratories. Here, we used plasma cfDNA sequencing data from 2,208 samples sent for non-invasive prenatal aneuploidy screening to detect CMV and precisely measure the length of CMV fragments in human plasma. CMV reads were identified in 120 (5.4%) samples. Median cfDNA fragment size derived from CMV was significantly shorter than cfDNA derived from human chromosomes (103 vs 172 bp, p < 0.0001), corresponding to the 3rd percentile of human cfDNA. Sequencing of cfDNA from seven plasma samples from transplant patients positive for CMV confirmed the extraordinarily short nature of CMV cfDNA fragment size with a median length of 149 bp. We further show that these high-resolution measurements of CMV DNA fragment size accurately predict measured discrepancies in serum viral load measurements by different qPCR assays. These results highlight the exceptionally fragmented nature of CMV cfDNA and illustrate the promise of plasma cfDNA sequencing for quantitating viral loads through detection of fragments that would be unrecoverable by qPCR.

Most neutralizing human monoclonal antibodies target novel epitopes requiring both Lassa virus glycoprotein subunits.

Lassa fever is a severe multisystem disease that often has haemorrhagic manifestations. The epitopes of the Lassa virus (LASV) surface glycoproteins recognized by naturally infected human hosts have not been identified or characterized. Here we have cloned 113 human monoclonal antibodies (mAbs) specific for LASV glycoproteins from memory B cells of Lassa fever survivors from West Africa. One-half bind the GP2 fusion subunit, one-fourth recognize the GP1 receptor-binding subunit and the remaining fourth are specific for the assembled glycoprotein complex, requiring both GP1 and GP2 subunits for recognition. Notably, of the 16 mAbs that neutralize LASV, 13 require the assembled glycoprotein complex for binding, while the remaining 3 require GP1 only. Compared with non-neutralizing mAbs, neutralizing mAbs have higher binding affinities and greater divergence from germline progenitors. Some mAbs potently neutralize all four LASV lineages. These insights from LASV human mAb characterization will guide strategies for immunotherapeutic development and vaccine design.

Heme-oxygenase induction inhibits arteriolar thrombosis in vivo: effect of the non-substrate inducer cobalt protoporphyrin.

Heme oxygenase-1 (HO) metabolizes heme to form the vasodilator carbon monoxide and antioxidant biliverdin. Upregulation of HO-1 by hemin, which is also a substrate attenuates thrombosis in rodent models, however, whether protection is due to HO-1 upregulation or to increased substrate availability is unknown. This study tested the hypothesis that treatment of mice with cobalt protoporphyrin (CoPP), a non-substrate HO-1 inducer, would protect the endothelium from laser injury. C57Bl/J6 mice were treated with vehicle, CoPP (20 mg/kg), CoPP plus the HO-1 inhibitor tin protoporphyrin (SnPP; 20 mg/kg) or SnPP alone for 18 h. Intravital microscopy was used to quantitate thrombus formation in cremaster arterioles in response to laser ablation of the endothelium. CoPP treatment inhibited thrombosis by 43% compared to vehicle (P<0.05). SnPP co-treatment negated the inhibitory effect of CoPP while SnPP alone potentiated thrombosis compared to vehicle. In CoPP-treated animals, cremaster HO-1 mRNA expression was increased 59+/-17-fold over vehicle (P<0.001). Co-treatment with CoPP+SnPP attenuated this effect by 36%, however the increase in HO-1 protein induced by CoPP was unaffected by SnPP. Induction of HO-1 by the non-substrate inducer CoPP protects against laser induced endothelial injury without the need for increased substrate. Small molecule, substrate-independent upregulation of HO-1 expression represents a feasible approach to ameliorate endothelial dysfunction in cardiovascular disease.