Children with sickle cell anemia (SCA) often develop hyposthenuria and renal hyperfiltration at an early age, possibly contributing to the glomerular injury and renal insufficiency commonly seen later in life. The Phase III randomized double-blinded Clinical Trial of Hydroxyurea in Infants with SCA (BABY HUG) tested the hypothesis that hydroxyurea can prevent kidney dysfunction by reducing hyperfiltration.
193 infants with SCA (mean age 13.8 months) received hydroxyurea 20 mg/kg/day or placebo for 24 months. 99mTc diethylenetriaminepentaacetic acid (DTPA) clearance, serum creatinine, serum cystatin C, urinalysis, serum and urine osmolality after parent-supervised fluid deprivation, and renal ultrasonography were obtained at baseline and at exit to measure treatment effects on renal function.
At exit children treated with hydroxyurea had significantly higher urine osmolality (mean 495 mOsm/kg H2O compared to 452 in the placebo group, p=0.007) and a larger percentage of subjects taking hydroxyurea achieved urine osmolality >500 mOsm/kg H2O. Moreover, children treated with hydroxyurea had smaller renal volumes (p=0.007). DTPA-derived glomerular filtration rate (GFR) was not significantly different between the two treatment groups, but was significantly higher than published norms. GFR estimated by the Chronic Kidney Disease in Children Schwartz formula was the best non-invasive method to estimate GFR in these children, as it was the closest to the DTPA-derived GFR.
Treatment with hydroxyurea for 24 months did not influence GFR in young children with SCA. However, hydroxyurea was associated with better urine concentrating ability and less renal enlargement, suggesting some benefit to renal function.
kidney function; glomerular filtration rate; urine osmolality; hydroxyurea
The laboratory and clinical benefits of hydroxyurea therapy for children with sickle cell anemia (SCA) are well recognized, but treatment in young patients is limited in part by concerns about long-term genotoxicity, and specifically possible carcinogenicity.
The Pediatric Hydroxyurea Phase III Clinical Trial (BABY HUG) was a multi-center double-blinded placebo-controlled randomized clinical trial (NCT00006400) testing whether hydroxyurea could prevent chronic organ damage in very young patients with SCA. An important secondary objective was the measurement of acquired genotoxicity using 3 laboratory assays: chromosomal karyotype, illegitimate VDJ recombination events, and micronucleated reticulocyte formation.
Our data indicate that hydroxyurea treatment was not associated with any significant increases in genotoxicity compared to placebo treatment.
These data provide additional support to the safety profile of hydroxyurea for young patients with SCA, and suggest that genotoxicity in this patient population is low.
genotoxicity; hydroxyurea; mutagenicity; sickle cell anemia
Youth infected with HIV at birth often have sleep disturbances, neurocognitive deficits, and abnormal psychosocial function which are associated with and possibly resulted from elevated blood cytokine levels that may lead to a decreased quality of life. To identify molecular pathways that might be associated with these disorders, we evaluated 38 HIV-infected and 35 uninfected subjects over 18-months for intracellular cytokine levels, sleep patterns and duration of sleep, and neurodevelopmental abilities. HIV infection was significantly associated with alterations of intracellular pro-inflammatory cytokines (TNF-α, IFN-γ, IL-12), sleep factors (total time asleep and daytime sleep patterns), and neurocognitive factors (parent and patient reported problems with socio-emotional, behavioral, and executive functions; working memory-mental fatigue; verbal memory; and sustained concentration and vigilance. By better defining the relationships between HIV infection, sleep disturbances, and poor psychosocial behavior and neurocognition, it may be possible to provide targeted pharmacologic and procedural interventions to improve these debilitating conditions.
pediatric HIV infection; intracellular cytokines; sleep behavior; neurodevelopment; neurocognition; path analysis
This study's purpose was to determine whether asthma medication use in HIV+ children is associated with HLA alleles. We reviewed HLA and medication data collected during the Women and Infants Transmission Study for 124 HIV+ children and their mothers. Analysis revealed that HLA-A68 (P=0.006) was independent and predictive for time to first asthma medication use. There was a preventive association of Cw6 (P=0.008) with AT. HAART was also associated with time to first asthma medication use (P=0.05). HLA alleles may modulate risk of developing a need for asthma medications and seem to function independently of the actions of HAART therapy.
To estimate whether HIV-infected pregnant women were at increased risk of hepatotoxicity when taking nevirapine (NVP) containing regimens compared to HIV-infected pregnant women taking antiretroviral therapy (ART) not containing NVP.
This analysis included HIV-infected pregnant women on ART from two multicenter, prospective cohorts: The Women and Infants Transmission Study (WITS) and the International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) protocol P1025. Multivariate Cox proportional hazards regression models were used to investigate the association between NVP use and hepatotoxicity. NVP use was dichotomized as use or no use and further categorized according to ART exposure history. We investigated two outcomes: any liver enzyme elevation (LEE) (grade 1-4) and severe LEE (grade 3-4).
A total of 1229 women with ART use during pregnancy were studied, 218 (17.7%) of whom received NVP. Among the women receiving NVP, 137 (62.8%) were NVP naïve. Twenty-nine women (13.3%) who received NVP developed any LEE and one (0.5%) developed severe LEE. Of the 1011 women on non-NVP regimens, 145 (14.3%) developed any LEE and 14 (1.4%) developed severe LEE. There were no maternal deaths. In univariate models, LEE was not significantly associated with CD4+ count > 250 cells/μL or NVP use. In adjusted multivariate models, no significant increased risk of LEE (any or severe) in women taking NVP was detected as compared to those taking other ART regardless of prior exposure history.
We did not observe an increased risk of hepatotoxicity among HIV-infected pregnant women on NVP versus other ART, including women who were ART naïve.
AIDS; antiretroviral therapy; hepatotoxicity; HIV; nevirapine; pregnancy; women
The spectrum of lung diseases associated with HIV is broad, and many infectious and noninfectious complications of HIV infection have been recognized. The nature and prevalence of lung complications have not been fully characterized since the Pulmonary Complications of HIV Infection Study more than 15 years ago, before antiretroviral therapy (ART) increased life expectancy. Our understanding of the global epidemiology of these diseases in the current ART era is limited, and the mechanisms for the increases in the noninfectious conditions, in particular, are not well understood. The Longitudinal Studies of HIV-Associated Lung Infections and Complications (Lung HIV) Study (ClinicalTrials.gov number NCT00933595) is a collaborative multi-R01 consortium of research projects established by the National Heart, Lung, and Blood Institute to examine a diverse range of infectious and noninfectious pulmonary diseases in HIV-infected persons. This article reviews our current state of knowledge of the impact of HIV on lung health and the development of pulmonary diseases, and highlights ongoing research within the Lung HIV Study.
HIV/AIDS; pulmonary infections; pulmonary complications; smoking
To investigate the possible effects of antiretroviral therapy (ART) in utero on cardiac development and function in HIV-negative children.
ART reduces vertical HIV transmission. Long-term cardiotoxicity after in utero exposure to ART is unknown in children but has occurred in young animals.
Using a prospective multi-site cohort study design, we compared echocardiograms taken between birth and 24 months in two groups of HIV-negative infants of HIV-positive mothers: 136 infants exposed to ART (ART+) and 216 unexposed infants (ART−).
Mean LV mass Z-scores were consistently lower in ART+ girls than in ART− girls: differences in mean Z-scores were −0.46 at birth (P=0.005), −1.02 at 6 months (P<0.001), −0.74 at 12 months (P<0.001), and −0.79 at 24 months (P<0.001). Corresponding differences in Z-scores for boys were smaller: 0.13 at 1 month (P=0.42), −0.44 at 6 months (P=0.01), −0.15 at 12 months (P=0.37), and −0.21 at 24 months (P=0.21). Septal wall thickness and LV dimension were smaller than expected in ART+ infants, but LV contractility was consistently about 1 SD higher at all ages (P<0.001). In ART+ infants, LV fractional shortening was higher than in ART− infants; girls showed a greater difference.
Fetal exposure to ART is associated with reduced LV mass, LV dimension, and septal wall thickness Z-scores and increased LV fractional shortening and contractility up to age 2 years. These effects are more pronounced in girls than in boys. Fetal ART exposure may impair myocardial growth while improving depressed LV function.
Pediatric; HIV; Antiretroviral Therapy; Cardiomyopathy
Immunoreconstitution of HIV-infected (HIV+) patients after treatment with highly antiretroviral therapy (HAART) appears to provoke inflammatory diseases.
Determine whether HIV+ children on HAART (HIV+ HAART+) have a higher incidence of asthma than HIV+ children not on HAART (HIV+ HAART−).
To investigate this possibility, 2,664 children (193 HIV+, 2,471 HIV−) born to HIV+ women were evaluated for the incidence and prevalence of asthma (i.e., asthma medication use), and change of CD4+ T cell percentage with time.
The HIV+ HAART+ children had higher CD4+ T cell percentages, lower CD8+ T cell percentages, and lower viral burdens than the HIV+ HAART− children (P≤0.05 to P≤0.01). The cumulative incidence of asthma medication use in HIV+ HAART+ children at 13.5 year rose to 33.5% vs. 11.5% in HIV+ HAART− children (hazard ratio=3.34, P=0.01) and was equal to that in the HIV− children. In children born prior to the HAART era, the prevalence of asthma medication use for HIV+ HAART+ children at 11 years of age was 10.4% vs. 3.8% for HIV+ HAART− children (odds ratio=3.38, P=0.02) and was equal to that of the HIV− children. The rate of change of CD4+ T cells (percent/year) around the time of first asthma medication for HIV+ HAART+ vs. HIV+ HAART− children was 0.81 vs. −1.43 (P=0.01).
The increased incidence of asthma in HIV+ HAART+ children may be driven by immunoreconstitution of CD4+ T cells.
This HIV model of pediatric asthma may yield clues to help explain the epidemic of asthma in the general pediatric population.
pediatric HIV infection; CD4+ T cell mediated induction of asthma; HAART-produced immunoreconstitution
Sickle cell anaemia (SCA) is associated with significant morbidity from acute complications and organ dysfunction beginning in the first year of life. In the first multicenter randomised double-blinded trial in very young children with SCA, the impact of hydroxyurea (hydroxycarbamide) therapy on organ dysfunction, clinical complications, and laboratory findings, and its toxicity, were examined.
Eligible subjects had HbSS or Sβ0thalassaemia, were age 9–18 months at randomisation, and were not selected for clinical severity. Subjects received liquid hydroxyurea, 20 mg/kg/day, or placebo for two years. Primary study endpoints were splenic function (qualitative uptake on 99Tc spleen scan) and renal function (glomerular filtration rate by 99mTc-DTPA clearance). Additional evaluations included: blood counts, HbF, chemistry profiles, spleen function biomarkers, urine osmolality, neurodevelopment, transcranial Doppler ultrasonography, growth, and mutagenicity. Study visits occurred every two to four weeks.
Ninety-six subjects received hydroxyurea and 97 placebo; 86% completed the study. Significant differences were not seen for the primary endpoints, but suggestive benefit was noted in quantitative measures of spleen function. Hydroxyurea significantly decreased pain and dactylitis with trends for decreased acute chest syndrome, hospitalisation and transfusion. Hydroxyurea increased haemoglobin and HbF and decreased WBC count. Toxicity was limited to mild-moderate neutropaenia.
Although hydroxyurea treatment did not reduce splenic and renal dysfunction assessed by primary endpoint measures, it resulted in major clinical benefit because of diminished acute complications, favorable haematologic results, and a lack of unexpected toxicities. Based on the safety and efficacy data from this trial, hydroxyurea can now be considered for all very young children with SCA.
Detectable HIV-1 RNA at delivery is the strongest predictor of mother-to-child transmission. The risk factors for detectable HIV, including type of regimen, are unknown. We evaluated factors, including highly active antiretroviral (HAART) regimen, associated with detectable HIV-1 RNA at delivery in the Women and Infants Transmission Study.
Data from 630 HIV-1 infected women who enrolled from 1998–2005 and received HAART during pregnancy were analyzed. Multivariable analyses examined associations between regimens, demographic factors, and detectable HIV-1 RNA (>400 cp/ml) at delivery.
Overall, 32% of the women in the cohort had detectable HIV-1 RNA at delivery. Among the subset of 364 HAART-experienced women, a lower CD4+ cell count at enrollment (adjusted odds ratio [AOR]=1.20 per 100 cells/μl, CI 1.04–1.37) and higher HIV-1 RNA at enrollment (AOR=1.52 per log10 cp/ml, CI 1.32–1.75) were significantly associated with detectable HIV-1 RNA levels at delivery. For the 266 HAART-naïve women, both lower CD4+ cell count at enrollment (AOR=1.24 per 100 cells/μl, CI 1.05–1.48) and higher HIV-1 RNA at enrollment (AOR=1.35 per log10 cp/ml, CI 1.12–1.63) were associated with detectable HIV-1 RNA at delivery. In addition, age at delivery (AOR=0.92 per 10y older, CI 0.86–0.99), and maternal illicit drug use (AOR=3.15, CI 1.34–7.41) were significantly associated with detectable HIV-1 RNA at delivery among HAART-naïve women. Type of HAART regimen was not significant in either group.
Lack of viral suppression at delivery was common in the WITS cohort, but differences by antiretroviral regimen were not identified. Despite a transmission rate below 1% in the last 5 years of the WITS cohort, improved measures to maximize HIV-1 RNA suppression at term among high-risk women are warranted.
antiretrovirals; HIV; pregnancy; MTCT; HAART
HRQL in IPF patients is impaired. Data from other respiratory diseases led us to hypothesize that significant gender differences in HRQL in IPF also exist.
Data were drawn from the NIH-sponsored Lung Tissue Research Consortium (LTRC). Demographic and pulmonary physiology data along with MMRC, SF12, and SGRQ scores from women versus men were compared with two-sample t-tests. Multivariate linear regression was used to examine the association between SF-12 component scores and gender while adjusting for other relevant variables.
The study sample consisted of 147 men and 74 women. Among several baseline variables, only DLCO% predicted differed between women and men, (43.7 vs 38.0, p=0.03). In general, men exhibited lower (better) MMRC scores (1.7 vs 2.4, p=0.02), particularly those with milder disease as measured by DLCO% predicted. In an adjusted analysis, SF-12 PCS scores in men were lower (worse) than women (p=0.01), an effect that was more pronounced in men with greater dyspnea scores. In a similar analysis, SF-12 MCS scores in women were lower than men (worse) (48.3 vs. 54.4, p=0.0004), an effect that was more pronounced in women with greater dyspnea scores.
Significant gender differences in HRQL exist in IPF. As compared to women, men reported less severe dyspnea, had worse SF-12 PCS scores, but better SF-12 MCS scores. Dyspnea appears to have a greater impact on the physical HRQL of men and the emotional HRQL of women. An improved understanding of the mechanism behind these differences is needed to better target interventions.
interstitial pulmonary fibrosis; gender; health-related quality of life
Evidence of the laboratory benefits of hydroxyurea and its clinical efficacy in reducing acute vaso-occlusive events in adults and children with sickle cell anemia has accumulated for more than 15 years. A definitive clinical trial showing that hydroxyurea can also prevent organ damage might support widespread use of the drug at an early age. BABY HUG is a randomized, double-blind placebo-controlled trial to test whether treating young children ages 9 to 17 months at entry with a liquid preparation of hydroxyurea (20 mg/kg/day for two years) can decrease organ damage in the kidneys and spleen by at least 50%. Creation of BABY HUG entailed unique challenges and opportunities. Although protection of brain function might be considered a more compelling endpoint, preservation of spleen and renal function has clinical relevance, and significant treatment effects might be discernable within the mandated sample size of two hundred. Concerns about unanticipated severe toxicity and burdensome testing and monitoring requirements were addressed in part by an internal Feasibility and Safety Pilot Study, the successful completion of which was required prior to enrolling a larger number of children on the protocol. Concerns over recruitment of potentially vulnerable subjects were allayed by inclusion of a research subject advocate, or ombudsman. Finally, maintenance of blinding of research personnel was aided by inclusion of an unblinded primary endpoint person, charged with transmitting endpoint data and monitoring blood work locally for toxicity. (ClinicalTrials.gov number,NCT00006400)
hydroxyurea; clinical trial; infants; sickle cell
To estimate whether the association between nevirapine (NVP) and hepatotoxicity differs according to pregnancy status in HIV-infected women.
This analysis included HIV-infected pregnant women on ART from two multicenter, prospective cohorts: The Women and Infants Transmission Study (WITS) and the International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) protocol P1025 and HIV-infected non-pregnant women from one multicenter, prospective cohort: The Women’s Interagency HIV Study (WIHS). Using multivariate Cox proportional hazards regression, the interaction between NVP and pregnancy status in terms of hepatotoxicity was investigated. NVP use was dichotomized as use or no use and was further categorized according to ART exposure history. We investigated two outcomes: any liver enzyme elevation (LEE) (grade 1-4) and severe LEE (grade 3-4).
Data on 2050 HIV-infected women taking ART were included, 1229 (60.0%) pregnant and 821 (40.0%) non-pregnant. Among the pregnant women, 174 (14.2%) developed any LEE and 15 (1.2%) developed severe LEE as compared to 75 (9.1%) and 5 (0.6%) respectively of the non-pregnant women. In multivariate adjusted models, NVP was not significantly associated with risk of LEE regardless of pregnancy status; however, pregnancy was associated with an increased risk of any LEE (RR 4.7, CI 3.4 – 6.5) and severe LEE (RR 3.8, CI 1.3 – 11.1). The association of pregnancy and LEE was seen regardless of prior ART and NVP exposure history.
No significant association between NVP and LEE was observed regardless of pregnancy status, but pregnancy was significantly associated with increased hepatotoxocity in HIV-infected women.
AIDS; antiretroviral therapy; hepatotoxicity; HIV; nevirapine; pregnancy; women
Airway hyperresponsiveness is the ability of airways to narrow excessively in response to inhaled stimuli and is a key feature of asthma. Airway inflammation and ventilation heterogeneity have been separately shown to be associated with airway hyperresponsiveness. A study was undertaken to establish whether ventilation heterogeneity is associated with airway hyperresponsiveness independently of airway inflammation in subjects with asthma and to determine the effect of inhaled corticosteroids on this relationship.
Airway inflammation was measured in 40 subjects with asthma by exhaled nitric oxide, ventilation heterogeneity by multiple breath nitrogen washout and airway hyperresponsiveness by methacholine challenge. In 18 of these subjects with uncontrolled symptoms, measurements were repeated after 3 months of treatment with inhaled beclomethasone dipropionate.
At baseline, airway hyperresponsiveness was independently predicted by airway inflammation (partial r2 = 0.20, p<0.001) and ventilation heterogeneity (partial r2 = 0.39, p<0.001). Inhaled corticosteroid treatment decreased airway inflammation (p = 0.002), ventilation heterogeneity (p = 0.009) and airway hyperresponsiveness (p<0.001). After treatment, ventilation heterogeneity was the sole predictor of airway hyperresponsiveness (r2 = 0.64, p<0.001).
Baseline ventilation heterogeneity is a strong predictor of airway hyperresponsiveness, independent of airway inflammation in subjects with asthma. Its persistent relationship with airway hyperresponsiveness following anti‐inflammatory treatment suggests that it is an important independent determinant of airway hyperresponsiveness. Normalisation of ventilation heterogeneity is therefore a potential goal of treatment that may lead to improved long‐term outcomes.
Concern for potential adverse effects of antiretroviral (ARV) chemotherapy used to prevent mother-to-child HIV transmission has led the US Public Health Service to recommend long-term follow-up of ARV-exposed children. Nucleoside reverse transcriptase inhibitor ARV agents can inhibit DNA polymerase γ, impairing mitochondrial DNA (mtDNA) synthesis and resulting in depletion or dysfunction.
We measured the mtDNA content of stored peripheral blood mononuclear cells (PBMCs) of 411 healthy children who were born to HIV-uninfected women and 213 uninfected infants who were born to HIV-infected women with or without in utero and neonatal ARV exposure. Cryopreserved PBMC mtDNA was quantified by using the Primagen Retina Mitox assay.
Geometric mean PBMC mtDNA levels were lower at birth in infants who were born to HIV-infected women. Among HIV-exposed children, mtDNA levels were lowest in those who were not exposed to ARVs, higher in those with exposure to zidovudine alone, and higher still in those with combination nucleoside reverse transcriptase inhibitor exposure. A similar pattern was observed in the corresponding women. Levels of mtDNA increased during the first 5 years of life in all HIV-exposed children but achieved normal levels only in those with ARV exposure.
Levels of mtDNA are lower than normal in HIV-exposed children. Contrary to expectation, PBMC mtDNA levels are significantly higher in ARV-exposed, HIV-uninfected infants and their infected mothers compared with ARV-unexposed infants and women. By 5 years, levels of PBMC mtDNA rise to normal concentrations in ARV-exposed children but remain depressed in ARV-unexposed children.
HIV; mitochondria; antiretroviral agents
Defining the precise cellular mechanisms of neutralization by potently inhibitory antibodies is important for understanding how the immune system successfully limits viral infections. We recently described a potently inhibitory monoclonal antibody (MAb E16) against the envelope (E) protein of West Nile virus (WNV) that neutralizes infection even after virus has spread to the central nervous system. Herein, we define its mechanism of inhibition. E16 blocks infection primarily at a post-attachment step as antibody-opsonized WNV enters permissive cells but cannot escape from endocytic compartments. These cellular experiments suggest that E16 blocks the acid-catalyzed fusion step that is required for nucleocapsid entry into the cytoplasm. Indeed, E16 directly inhibits fusion of WNV with liposomes. Additionally, low-pH exposure of E16–WNV complexes in the absence of target membranes did not fully inactivate infectious virus, further suggesting that E16 prevents a structural transition required for fusion. Thus, a strongly neutralizing anti–WNV MAb with therapeutic potential is potently inhibitory because it blocks viral fusion and thereby promotes clearance by delivering virus to the lysosome for destruction.
Antibodies are essential components of the immune response against many pathogens, including viruses. A greater understanding of the mechanisms by which the most strongly inhibitory antibodies act may influence the design and production of novel vaccines or antibody-based therapies. Our group recently generated a highly inhibitory monoclonal antibody (E16) against the envelope protein of West Nile virus, which can abort infection in animals even after the virus has spread to the brain. In this paper, we define its mechanism of action. We show that E16 blocks infection by preventing West Nile virus from transiting from endosomes, an obligate step in the entry pathway of the viral lifecycle. Thus, a strongly inhibitory anti–West Nile virus antibody is highly neutralizing because it blocks fusion and delivers virus to the lysosome for destruction.
Like CD1d-restricted iNKT cells, mucosal-associated invariant T cells (MAITs) are “innate” T cells that express a canonical TCRα chain, have a memory phenotype, and rapidly secrete cytokines upon TCR ligation. Unlike iNKT cells, MAIT cells require the class Ib molecule MHC-related protein I (MR1), B cells, and gut flora for development and/or expansion, and they preferentially reside in the gut lamina propria. Evidence strongly suggests that MAIT cell activation is ligand-dependent, but the nature of MR1 ligand is unknown. In this study, we define a mechanism of endogenous antigen presentation by MR1 to MAIT cells. MAIT cell activation was dependent neither on a proteasome-processed ligand nor on the chaperoning by the MHC class I peptide loading complex. However, MAIT cell activation was enhanced by overexpression of MHC class II chaperones Ii and DM and was strikingly diminished by silencing endogenous Ii. Furthermore, inhibiting the acidification of the endocytic compartments reduced MR1 surface expression and ablated MAIT cell activation. The importance of the late endosome for MR1 antigen presentation was further corroborated by the localization of MR1 molecules in the multivesicular endosomes. These findings demonstrate that MR1 traffics through endocytic compartments, thereby allowing MAIT cells to sample both endocytosed and endogenous antigens.
Previous studies have suggested that monoclonal antibodies (MAbs) to flavivirus nonstructural protein-1 (NS-1) protect against infection in mice through an Fc-γ receptor-dependent pathway. To identify a specific mechanism, we evaluated the protective activity of anti-NS1 MAbs to WNV using mice and cells with deficiencies of specific Fc-γ receptors. Our results suggest that only MAbs that recognize cell surface-associated NS1 trigger Fc-γ receptor I- and/or IV-mediated phagocytosis and clearance of WNV-infected cells. These findings may be relevant for generating novel therapeutic MAbs or vaccines against flaviviruses that target the NS1 protein.
The flavivirus nonstructural protein NS1 is a highly conserved secreted glycoprotein that does not package with the virion. Immunization with NS1 elicits a protective immune response against yellow fever, dengue, and tick-borne encephalitis flaviviruses through poorly defined mechanisms. In this study, we purified a recombinant, secreted form of West Nile virus (WNV) NS1 glycoprotein from baculovirus-infected insect cells and generated 22 new NS1-specific monoclonal antibodies (MAbs). By performing competitive binding assays and expressing truncated NS1 proteins on the surface of yeast (Saccharomyces cerevisiae) and in bacteria, we mapped 21 of the newly generated MAbs to three NS1 fragments. Prophylaxis of C57BL/6 mice with any of four MAbs (10NS1, 14NS1, 16NS1, and 17NS1) strongly protected against lethal WNV infection (75 to 95% survival, respectively) compared to saline-treated controls (17% survival). In contrast, other anti-NS1 MAbs of the same isotype provided no significant protection. Notably, 14NS1 and 16NS1 also demonstrated marked efficacy as postexposure therapy, even when administered as a single dose 4 days after infection. Virologic analysis showed that 17NS1 protects at an early stage in infection through a C1q-independent and Fc γ receptor-dependent pathway. Interestingly, 14NS1, which maps to a distinct region on NS1, protected through a C1q- and Fc γ receptor-independent mechanism. Overall, our data suggest that distinct regions of NS1 can elicit protective humoral immunity against WNV through different mechanisms.