Impact of Distinct Therapies on Antibody Response to SARS-CoV-2 Vaccine in Systemic Lupus Erythematosus.

OBJECTIVE: To date, the only study that has assessed the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 mRNA) vaccine in systemic lupus erythematosus (SLE) observed a moderate response, but the sample size precluded an accurate analysis of the effect of individual drugs. Therefore, we evaluated the immunogenicity of an inactivated SARS-CoV-2 vaccine (Sinovac-CoronaVac) and the influence of different medications in SLE. Safety was also assessed. METHODS: We conducted a prospective controlled study of 232 SARS-CoV-2-naive SLE patients and 58 SARS-CoV-2-naive controls who were vaccinated with 2 doses of Sinovac-CoronaVac with a 28-day interval (day 0/day 28 [D0/D28]). Immunogenicity analysis at D0/D28 and D69 included anti-SARS-CoV-2 S1/S2 IgG seroconversion (SC) and neutralizing antibodies (NAb) positivity. The influence of individual drugs on immune response and safety was assessed. RESULTS: Patients and controls were well balanced for age (P = 0.771). At D69, SLE patients showed a moderate SC (70.2% versus 98.1%; P < 0.001) and moderate frequency of NAb positivity (61.5% versus 84.6%; P = 0.002), although both frequencies were lower than in controls. Factors associated with lower SC in univariate analysis at D69 were prednisone use (odds ratio [OR] 0.215 [95% confidence interval (95% CI) 0.108-0.427], P < 0.001) and mycophenolate mofetil (MMF) use (OR 0.201 [95% CI 0.107-0.378], P < 0.001), whereas hydroxychloroquine (HCQ) use led to a 2.5 increase in SC (P = 0.011). SLE patients who were receiving HCQ monotherapy had similar SC to controls at D69 (100% versus 98.1%; P = 1.000). In multivariate analysis, prednisone and MMF use were independently associated with lower SC (P < 0.001) and NAb positivity (P < 0.001). Safety analysis revealed no moderate/severe adverse events. CONCLUSION: Sinovac-CoronaVac has a moderate immunogenicity in SARS-CoV-2-naive SLE patients with an excellent safety profile. We further demonstrate that HCQ may improve SC, whereas prednisone and MMF had a major deleterious effect in vaccine response, reinforcing the need to investigate the role of temporary MMF withdrawal or a vaccine-booster dose (ClinicalTrials.gov identifier: NCT04754698).

Surrogate test performance for SARS-CoV-2 neutralizing antibodies (nAbs) for convalescent plasma (CCP): How useful could they be?

BACKGROUND: COVID-19 high-titer CCP selection is a concern, because neutralizing antibody (nAb) testing requires sophisticated labs and methods. Surrogate tests are an alternative for measuring nAb levels in plasma bags, including those that are pathogen-reduced. STUDY DESIGN/METHODS: We studied a panel consisting of 191 samples from convalescent donors tested by nAb (CPE-VNT), obtained from 180 CCP donations (collection: March 20-January 21) and 11 negative controls, with a total of 80 and 111 serum and plasma samples (71 amotosalen/UV treated), with nAb titers ranging from negative to 10,240. Samples were blindly tested for several surrogates: one anti-RBD, two anti-spike, and four anti-nucleocapsid tests, either isolated or combined to improve their positive predictive values as predictors of the presence of high-titer nAbs, defined as those with titers ≥160. RESULTS: Except for combined and anti-IgA/M tests, all isolated surrogate tests showed excellent performance for nAb detection: sensitivity (98.3%-100%), specificity (85.7%-100%), PPV (98.9%-100%), NPV (81.3%-100%), and AUC (0.93-0.96), with a variable decrease in sensitivity and considerably lower specificity when using FDA authorization and concomitant nAb titers ≥160. All surrogates had AUCs that were statistically different from CPE-VNT if nAb≥160, including when using combined, orthogonal approaches. CONCLUSIONS: Surrogate tests (isolated or in combination) have an indirect good performance in detecting the presence of nAb, with lower sensitivity and specificity when high nAb titer samples are used, possibly accepting a considerable number of donors whose nAb titers are actually low, which should be evaluated by each laboratory responsible for CCP collection.

Hibridación de anticuerpos en la Covid-19 / Antibody hybridization in Covid-19

Introducción: El nuevo coronavirus tiene material genético. Esto permite a un receptor transformarse en el sitio de acción polibásica y es capaz de infectar a través de múltiples receptores de entrada y resaltar a las proteínas de tipo espiga (S). La proteína 'espiga' es una proteína de fusión viral de la Covid-19, es por ello que en la búsqueda terapéutica se establece las siguientes preguntas, ¿la hibridación de anticuerpos logrará ganar la guerra contra la pandemia de la Covid-19?; o ¿el plasma rico en anticuerpos puede mantener a las personas fuera de las unidades de cuidados intensivos? Estas preguntas radican en que los estudios actuales no establecen la verdadera utilidad de la terapia inmunológica. Objetivo: Presentar la utilidad de anticuerpos híbridos ante la actual pandemia de la Covid-19 y otros coronavirus. Métodos: Se desarrolló una revisión bibliográfica a partir de la evidencia existente acerca del panorama de la proteómica en el estudio del sistema inmune para combatir infecciones. Se utilizó un margen de tiempo entre el año 1999 al 2020. Se seleccionaron un total de 37 documentos que cumplen con los protocolos de inclusión en idioma inglés o español; en la búsqueda se utilizaron términos MeSH. Se escogieron estudios de orden observacional o analíticos; de carácter experimental, reporte de casos que dataran aspectos bioquímicos, biológicos, patológicos y clínicos del sistema inmune como blanco terapéutico ante la pandemia actual. El análisis documental fue realizado por el Grupo de Investigación en Salud de la Universidad del Cauca-Popayán, con apoyo y dirección de la Universidad de Houston, Texas (EEUU), con el apoyo de profesorado del Programa de Investigación Humana de la NASA. Resultados: La respuesta positiva para controlar esta pandemia está basada en los cuidados preventivos y en las posibles terapias innovadoras ante los nuevos coronavirus que logren transmitirse de animales a humanos. Se resalta el posible uso de anticuerpos de dominio único híbridos para frenar infecciones víricas nuevas. Conclusiones: Se resalta el posible uso de anticuerpos de dominio único híbridos para frenar infecciones víricas nuevas(AU)

Introduction: The new coronavirus has genetic material. This allows a receptor to transform into the polybasic site of action and it is capable of infecting through multiple entry receptors and highlighting spike-like (S) proteins. The spike protein is a viral fusion protein of Covid-19, which is why in the therapeutic search the following questions are established, will antibody hybridization succeed in winning the war against the Covid-19 pandemic? Or can antibody-rich plasma keep people out of intensive care units? These questions are that current studies do not establish the true utility of immune therapy. Objective: To settle the usefulness of hybrid antibodies to the current Covid-19 pandemic and other coronaviruses. Methods: A bibliographic review was developed from the existing evidence about the panorama of proteomics in the study of the immune system to fight infections. A time frame was used between 1999 and 2020. A total of 37 documents, in English or Spanish, that comply with the inclusion protocols were selected; MeSH terms were used in the search. Observational or analytical studies were chosen; experimental, case report dating biochemical, biological, pathological and clinical aspects of the immune system as a therapeutic target in the current pandemic. The documentary analysis was carried out by the Health Research Group of the Universidad del Cauca-Popayán, with the support and direction of the University of Houston, Texas (USA), with the support of faculty from NASA Human Research Program. Results: The positive response to control this pandemic is based on preventive care and possible innovative therapies for the new coronaviruses that manage to be transmitted from animals to humans. Conclusions: The possible use of hybrid single domain antibodies to stop new viral infections is highlighted(AU)

Neutralising antibody escape of SARS-CoV-2 spike protein: Risk assessment for antibody-based Covid-19 therapeutics and vaccines.

The Spike protein is the target of both antibody-based therapeutics (convalescent plasma, polyclonal serum, monoclonal antibodies) and vaccines. Mutations in Spike could affect efficacy of those treatments. Hence, monitoring of mutations is necessary to forecast and readapt the inventory of therapeutics. Different phylogenetic nomenclatures have been used for the currently circulating SARS-CoV-2 clades. The Spike protein has different hotspots of mutation and deletion, the most dangerous for immune escape being the ones within the receptor binding domain (RBD), such as K417N/T, N439K, L452R, Y453F, S477N, E484K, and N501Y. Convergent evolution has led to different combinations of mutations among different clades. In this review we focus on the main variants of concern, that is, the so-called UK (B.1.1.7), South African (B.1.351) and Brazilian (P.1) strains.

Seroconversion and Abundance of IgG Antibodies against S1-RBD of SARS-CoV-2 and Neutralizing Activity in the Chilean Population.

COVID-19 is a pandemic caused by SARS-CoV-2. In Chile, half a million people have been infected and more than 16,000 have died from COVID-19. As part of the clinical trial NCT04384588, we quantified IgG against S1-RBD of SARS-CoV-2 (anti-RBD) in recovered people in Santiago and evaluated their suitability as COVID-19 convalescent plasma donors. ELISA and a luminescent SARS-CoV-2 pseudotype were used for IgG and neutralizing antibody quantification. 72.9% of the convalescent population (468 of 639) showed seroconversion (5-55 µg/mL anti-RBD IgG) and were suitable candidates for plasma donation. Analysis by gender, age, and days after symptom offset did not show significant differences. Neutralizing activity correlated with an increased concentration of anti-RBD IgG (p < 0.0001) and showed a high variability between donors. We confirmed that the majority of the Chilean patients have developed anti-SARS-CoV-2 antibodies. The quantification of anti-RBD IgG in convalescent plasma donors is necessary to increase the detection of neutralizing antibodies.

A new passive immune strategy based on IgY antibodies as a key element to control neonatal calf diarrhea in dairy farms.

BACKGROUND: Neonatal diarrhea remains one of the main causes of morbi-mortality in dairy calves under artificial rearing. It is often caused by infectious agents of viral, bacterial, or parasitic origin. Cows vaccination and colostrum intake by calves during the first 6 h of life are critical strategies to prevent severe diarrhea but these are still insufficient. Here we report the field evaluation of a product based on IgY antibodies against group A rotavirus (RVA), coronavirus (CoV), enterotoxigenic Escherichia coli, and Salmonella sp. This product, named IgY DNT, has been designed as a complementary passive immunization strategy to prevent neonatal calf diarrhea. The quality of the product depends on the titers of specific IgY antibodies to each antigen evaluated by ELISA. In the case of the viral antigens, ELISA antibody (Ab) titers are correlated with protection against infection in calves experimentally challenged with RVA and CoV (Bok M, et al., Passive immunity to control bovine coronavirus diarrhea in a dairy herd in Argentina, 2017), (Vega C, et al., Vet Immunol Immunopathol, 142:156-69, 2011), (Vega C, et al., Res Vet Sci, 103:1-10, 2015). To evaluate the efficiency in dairy farms, thirty newborn Holstein calves were randomly assigned to IgY DNT or control groups and treatment initiated after colostrum intake and gut closure. Calves in the IgY DNT group received 20 g of the oral passive treatment in 2 L of milk twice a day during the first 2 weeks of life. Animals were followed until 3 weeks of age and diarrhea due to natural exposure to infectious agents was recorded during all the experimental time. RESULTS: Results demonstrate that the oral administration of IgY DNT during the first 2 weeks of life to newborn calves caused a delay in diarrhea onset and significantly reduced its severity and duration compared with untreated calves. Animals treated with IgY DNT showed a trend towards a delay in RVA infection with significantly shorter duration and virus shedding compared to control calves. CONCLUSIONS: This indicates that IgY DNT is an effective product to complement current preventive strategies against neonatal calf diarrhea in dairy farms. Furthermore, to our knowledge, this is the only biological product available for the prevention of virus-associated neonatal calf diarrhea.

Immunoglobulin Therapy in a Patient With Severe Chikungunya Fever and Vesiculobullous Lesions.

Chikungunya virus (CHIKV) is an emerging arbovirus whose transmission has already been reported in several countries. Although the majority of individuals acutely infected with CHIKV appear to become asymptomatic, reports showing the occurrence of atypical and severe forms of the disease are increasing. Among them, the neurological and skin manifestations require medical attention. Treatment of CHIKV infection is almost symptomatic. In this sense, we report the case of a 56-years-old man who presented fever, headaches, paresthesia and pain in the right arm with visible red spots on the skin starting 30 days before Hospital admission. Tests determined Chikungunya infection and excluded other co-morbidities. Disease evolved with edema in hands and feet and extensive hemorrhagic bullous lesions on the skin of upper and lower limbs. Variations in hematological counts associated with liver dysfunction determined this patient's admission to the Intensive Care Unit. Then, he received intravenous antibiotic and immunoglobulin therapy (400 mg/Kg/day for the period of 5 days) with total recovery from the lesions after 10 days of follow-up. A general improvement in blood cell count and successful wound healing was observed. After discharge, no other clinical sign of the disease was reported until nowadays. This case reports for the first time the successful administration of intravenous immunoglobulin therapy to a patient with severe atypical dermatological form of Chikungunya Fever without any associated comorbidity.

A non-randomized multicentre trial of human immune plasma for treatment of hantavirus cardiopulmonary syndrome caused by Andes virus.

BACKGROUND: In Chile, Andes virus (ANDV) is the sole aetiological agent of hantavirus cardiopulmonary syndrome (HCPS) with mean annual incidence of 55 cases, 32% case fatality rate (CFR) and no specific treatment. Neutralizing antibody (NAb) titres at hospital admission correlate inversely with HCPS severity. We designed an open trial to explore safety and efficacy and evaluate pharmacokinetics of immune plasma as a treatment strategy for this disease. METHODS: We performed plasmapheresis on donors at least 6 months after HCPS and measured NAb titres through a focus-reduction neutralization test. Subjects admitted to 10 study sites with suspected/confirmed HCPS were eligible for treatment with immune plasma by intravenous infusion at an ANDV NAb dose of 5,000 U/kg. HCPS was confirmed through immunoglobulin M serology or reverse transcriptase-PCR. The main outcome was mortality within 30 days. RESULTS: From 2008-2012, we enrolled and treated 32 cases and confirmed HCPS in 29. CFR of hantavirus plasma-treated cases was 4/29 (14%); CFR of non-treated cases in the same period in Chile was 63/199 (32%; P=0.049, OR=0.35, CI=0.12, 0.99); CFR of non-treated cases at the same study sites between 2005-2012 was 18/66 (27%; (P=0.15, OR=0.43, CI=0.14, 1.34) and CFR in a previous methylprednisolone treatment study was 20/60 (33%; P=0.052, OR=0.32, CI=0.10, 1.00). We detected no serious adverse events associated to plasma infusion. Plasma NAb titres reached in recipients were variable and viral load remained stable. CONCLUSIONS: Human ANDV immune plasma infusion appears safe for HCPS. We observed a decrease in CFR in treated cases with borderline significance that will require further studies for confirmation.

Update on human rabies in a dog- and fox-rabies-free country.

UNLABELLED: Rabies is responsible for 50,000 deaths per year worldwide. Mainland France has been officially freed from rabies in non-flying animals since 2001. METHOD: We wanted to provide an update on the French situation, using published data, and describe possible options since official guidelines are lacking. RESULTS: Post-exposure prophylaxis (PEP) (early and careful cleaning and dressing of the wound, vaccination, and in case of high-risk exposure, injection of specific anti-rabies immunoglobulins) is known to be efficient except in rare cases. It is recommended after grade II contact (+specific immunoglobulins in immunodepressed patients), or grade III contact (vaccination+immunoglobulins). DISCUSSION: Mainland France being rabies-free, 3 options may be considered in case of bite by a dog or a cat that cannot be monitored in France: (a) consider the risk of rabies as null, so no PEP should be administrated, whatever the severity of bites; (b) consider there is a weak but lethal risk, so the international recommendations should be applied, using immunoglobulins in some cases; (c) consider that the risk is extremely low but cannot be excluded, and that the patient should be vaccinated to be protected, but without adding immunoglobulins (whether in case of grade II or III bites). CONCLUSION: There are no national guidelines for rabies in France, and so the physician managing the patient is the one who will decide to treat or not.

Treatment of mice with human monoclonal antibody 24h after lethal aerosol challenge with virulent Venezuelan equine encephalitis virus prevents disease but not infection.

We recently described a Venezuelan equine encephalitis virus (VEEV)-specific human monoclonal antibody (MAb), F5 nIgG, that recognizes a new neutralization epitope on the VEEV E2 envelope glycoprotein. In this study, we investigated the ability of F5 nIgG given prophylactically or therapeutically to protect mice from subcutaneous or aerosolized VEEV infection. F5 nIgG had potent ability to protect mice from infection by either route when administered 24h before exposure; however, mice treated 24h after aerosol exposure developed central nervous system infections but exhibited no clinical signs of disease. Infectious virus, viral antigen and RNA were detected in brains of both treated and untreated mice 2-6 days after aerosol exposure but were cleared from the brains of treated animals by 14-28 days after infection. This fully human MAb could be useful for prophylaxis or immediate therapy for individuals exposed to VEEV accidentally in the laboratory or during a deliberate release.

Development of a novel monoclonal antibody with reactivity to a wide range of Venezuelan equine encephalitis virus strains.

BACKGROUND: There is currently a requirement for antiviral therapies capable of protecting against infection with Venezuelan equine encephalitis virus (VEEV), as a licensed vaccine is not available for general human use. Monoclonal antibodies are increasingly being developed as therapeutics and are potential treatments for VEEV as they have been shown to be protective in the mouse model of disease. However, to be truly effective, the antibody should recognise multiple strains of VEEV and broadly reactive monoclonal antibodies are rarely and only coincidentally isolated using classical hybridoma technology. RESULTS: In this work, methods were developed to reliably derive broadly reactive murine antibodies. A phage library was created that expressed single chain variable fragments (scFv) isolated from mice immunised with multiple strains of VEEV. A broadly reactive scFv was identified and incorporated into a murine IgG2a framework. This novel antibody retained the broad reactivity exhibited by the scFv but did not possess virus neutralising activity. However, the antibody was still able to protect mice against VEEV disease induced by strain TrD when administered 24 h prior to challenge. CONCLUSION: A monoclonal antibody possessing reactivity to a wide range of VEEV strains may be of benefit as a generic antiviral therapy. However, humanisation of the murine antibody will be required before it can be tested in humans.

Validation of a virus neutralization potency test in BHK-21 cells for rabies immunoglobulins in a two-center study.

A rabies virus neutralization potency test (VNPT), adapted to microplates from the rapid fluorescent focus inhibition test (RFFIT) for rabies therapeutic immunoglobulin potency evaluation, was standardized and validated in a two-center study in Brazil. The two institutes involved in the study were: Instituto Nacional de Controle de Qualidade em Saúde (Fundação Oswaldo Cruz) and Instituto Butantan. Two equine rabies immunoglobulin samples, all diluted to 1IU/ml, were tested against the WHO 2nd Rabies Human Ig International Standard. Four dilutions of the samples and standards were tested with the VNPT. The potency of the samples was calculated in IU/ml using the probit method; linearity, accuracy, repeatability (intra-assay variation), intermediate precision (inter-assay variation) and reproducibility (inter-laboratory variation) were assessed to evaluate the reliability of the VNPT. Laboratories were arbitrarily coded as Laboratory A and Laboratory B. The following results were obtained with the International Standard: (a) linearity, the overall coefficient of correlation of the dose-response curve was -0.97; (b) accuracy, % error of -0.70 (IU/ml); (c) repeatability, 17.06% (Laboratory A) and 11.61% (Laboratory B); (d) intermediate precision, 16.99% (Laboratory A) and 22.05% (Laboratory B); (e) reproducibility, 14.5%. The final conclusion was that VNPT presents satisfactory linearity, accuracy, repeatability, intermediate precision and reproducibility and is a reliable and suitable method by which to evaluate rabies immunoglobulin potency.

Treatment of Argentine hemorrhagic fever.

Argentine hemorrhagic fever (AHF) is a rodent-borne illness caused by the arenavirus Junin that is endemic to the humid pampas of Argentina. AHF has had significant morbidity since its emergence in the 1950s, with a case-fatality rate of the illness without treatment between 15% and 30%. The use of a live attenuated vaccine has markedly reduced the incidence of AHF. Present specific therapy involves the transfusion of immune plasma in defined doses of neutralizing antibodies during the prodromal phase of illness. However, alternative forms of treatment are called for due to current difficulties in early detection of AHF, related to its decrease in incidence, troubles in maintaining adequate stocks of immune plasma, and the absence of effective therapies for severely ill patients that progress to a neurologic-hemorrhagic phase. Ribavirin might be a substitute for immune plasma, provided that the supply is guaranteed. Immune immunoglobulin or monoclonal antibodies should also be considered. New therapeutic options such as those being developed for systemic inflammatory syndromes should also be valuated in severe forms of AHF.

A humanized murine monoclonal antibody protects mice either before or after challenge with virulent Venezuelan equine encephalomyelitis virus.

A humanized monoclonal antibody (mAb) has been developed and its potential to protect from or cure a Venezuelan equine encephalomyelitis virus (VEEV) infection was evaluated. The VEEV-neutralizing, protective murine mAb 3B4C-4 was humanized using combinatorial antibody libraries and phage-display technology. Humanized VEEV-binding Fabs were evaluated for virus-neutralizing capacity, then selected Fabs were converted to whole immunoglobulin (Ig) G1, and stable cell lines were generated. The humanized mAb Hy4-26C, designated Hy4 IgG, had virus-neutralizing capacity similar to that of 3B4C-4. Passive antibody protection studies with purified Hy4 IgG were performed in adult Swiss Webster mice. As little as 100 ng Hy4 IgG protected 90 % of mice challenged with 100 intraperitoneal (i.p.) mean morbidity (MD(50)) doses of virulent VEEV (Trinidad donkey) 24 h after antibody transfer; also, 500 mug Hy4 IgG protected 80 % of mice inoculated with 100 intranasal MD(50) doses of VEEV. Moreover, 10 mug passive Hy4 IgG protected 70 % of mice from a VEEV challenge dose as great as 10(7) i.p. MD(50). Hy4 IgG also protected mice from challenge with another epizootic VEEV variety, 1C (P676). Importantly, therapeutic administration of the humanized mAb to mice already infected with VEEV cured 90 % of mice treated with Hy4 IgG within 1 h of VEEV inoculation and 75 % of mice treated 24 h after virus infection.

Varicella Zoster: aspectos clínicos e abordagem terapêutica da neuralgia pós-herpética / Varicella Zoster: clinical features and therapeutical approach of the post herpetic neuralgia

O presente artigo busca informar o médico generalista sobre os aspectos clínicos da infecção causada pelo vírus varicela zoster. O autor cita o comportamento viral de inatividade nos gânglios das raízes dorsais e as causas prováveis para sua reativação, tais como idade avançada, ou extremamente precoce, doenças do sistema imunológico e determinados tumores entre outras circunstâncias, que são capazes de propiciar condições para a reinfecção conhecida como herpes zoster, cujas características clínicas são também apresentadas, bem como seu diagnóstico e tratamento. As complicações neurológicas relacionadas à infecção pelo vírus varicela zoster são estudadas no artigo. É feita, ainda, a conceituação da neuralgia pós-herpética, e a atualização da abordagem terapêutica deste tipo de dor neuropática. São estudados os vários fatores fisiopatológicos responsáveis por sua gênese, cujo conhecimento fundamenta o tratamento medicamentoso eficiente.

The aim of the present article is to inform the internist on the clinical aspects of the varicella zoster virus infection. The author refers the viral inactivity behavior, harbored in the dorsal root ganglia. The probable causes to its reactivation are mentioned, such as advanced or very precocious age, immunocompromised states and some tumors among other circunstances. These conditions are capable to create the right enviromnent to the reinfection, called herpes zoster, whose clinical aspects, diagnosis and treatment are presented. The neurological complications related to the Varicella Zoster Virus infection are studied in the article. The post herpetic neuralgia is defined as a specific type of naturopathic pain. The author brings up to date the therapeutical approach of the painful condition caused by herpes zoster and emphasizes the significance of understanding the post herpetic neuralgia pathophysiologic mechanisms to its effective treatment.

Development of a monoclonal antibody specific to a recombinant envelope protein from dengue virus type 4 expressed in Pichia pastoris.

A mouse monoclonal antibody (MAb, 4B6) was able to recognize dengue virus type 4 envelope (E) protein both as a recombinant protein in Pichia pastoris and when it was present in infected brains of suckling mice. 4B6 was characterized by enzyme-linked immunoadsorbent assay (ELISA), hemaglutination inhibition, neutralization, and immunoblot. The MAb was isotyped as IgG2a. It was serotype 4 specific and it inhibited hemaglutination and neutralized homologous virus. It did not enhance infection of P338D1 cells by dengue type 4 virus strain H-241 strain. This MAb was reactive with recombinant E protein and dengue 4 virus, as revealed by Western blot. In vivo, MAb 4B6 conferred passive protection in mice challenged with homologous virus. Currently, this MAb is being used to purify recombinant E protein for further studies.