2Dengue disease is caused by four different flavivirus 1 serotypes, which infect 390 million people yearly with 25% symptomatic cases 2 and for which no licensed vaccine is available. Recent phase III vaccine trials showed partial protection, and in particular no protection for dengue virus serotype 2 (DENV--2) 3,4 . Structural studies so far have characterized only epitopes recognized by serotype specific human antibodies 5,6 . We recently isolated human antibodies potently neutralizing all four DENV serotypes 7 . Here we describe the X--ray structures of four of these broadly neutralizing antibodies (bnAbs) in complex with the envelope glycoprotein E from DENV--2, revealing that the recognition determinants are at a serotype conserved site at the E dimer interface, including the exposed main chain of the E fusion loop 8 and the two conserved glycan chains.This "E--dimer dependent epitope" (EDE) is also the binding site for the viral glycoprotein prM during virus maturation in the secretory pathway of the infected cell 9 , explaining its conservation across serotypes and highlighting an Achilles heel of the virus with respect to antibody neutralization. These findings will be instrumental for devising novel immunogens to protect simultaneously against all four serotypes of dengue virus.Exposed at the surface of infectious mature DENV particles, protein E is the sole target of neutralizing antibodies. It displays an icosahedral arrangement in which 90 E dimers completely coat the viral surface 10,11 and which is sensitive to the environmental pH. Upon entry of DENV into cells via receptor--mediated endocytosis, the acidic 3 endosomal environment triggers an irreversible fusogenic conformational change in E that leads to fusion of viral and endosomal membranes 1 . The structure of the isolated E dimer has been determined by X--ray crystallography using the soluble ectodomain (sE) 8,12 . Protein E is relatively conserved, displaying about 65% amino acid sequence identity when comparing the most distant DENV serotypes. In particular, there are two conserved N--linked glycosylation sites at positions N67 and N153. To examine its interaction with the antibodies, we selected four highly potent bnAbs identified in the accompanying work: 747(4) A11 and 747 B7 (EDE2 group, requiring glycosylation at position N153 for efficient binding) and 752--2 C8 and 753(3) C10 (EDE1 group, binding regardless of the glycosylation at N153) 7 -referred to as A11, B7, C8 and C10 from hereon. The EDE2 bnAbs were isolated from the same patient (who had a secondary infection with DENV--2), and are somatic variants of the same IgG clone, derived from the IGHV3--74 and IGLV2--23 germ lines. The heavy chain has a very long (26 amino acids, IMGT convention) complementarity--determining region 3 (CDR H3). The EDE1 bnAbs were isolated from different patients and derive from (EDE1 C8, the patient appeared to have a primary infection of undetermined serotype) and IGHV1--3* and IGLV2--14 (EDE1 C10, from a patient with secondary DENV--1 infecti...

It is of paramount importance to evaluate the prevalence of both asymptomatic and symptomatic cases of SARS-CoV-2 infection and their differing antibody response profiles. Here, we performed a pilot study of four serological assays to assess the amounts of anti-SARS-CoV-2 antibodies in serum samples obtained from 491 healthy individuals prior to the SARS-CoV-2 pandemic, 51 individuals hospitalized with COVID-19, 209 suspected cases of COVID-19 with mild symptoms, and 200 healthy blood donors. We used two ELISA assays that recognized the full-length nucleoprotein (N) or trimeric spike (S) protein ectodomain of SARS-CoV2. In addition, we developed the S-Flow assay that recognized the S protein expressed at the cell surface using flow cytometry, and the Luciferase Immunoprecipitation System (LIPS) assay that recognized diverse SARS-CoV-2 antigens including the S1 domain and the C-terminal domain of N by immunoprecipitation. We obtained similar results with the four serological assays. Differences in sensitivity were attributed to the technique and the antigen used. High anti-SARS-CoV-2 antibody titers were associated with neutralization activity, which was assessed using infectious SARS-CoV-2 or lentiviral-S pseudotype virus. In hospitalized patients with COVID-19, seroconversion and virus neutralization occurred between 5 and 14 days after symptom onset, confirming previous studies. Seropositivity was detected in 32% of mildly-symptomatic individuals within 15 days of symptom onset and in 3% of healthy blood donors. The four antibody assays we used enabled a broad evaluation of SARS-CoV-2 seroprevalence and antibody profiling in different subpopulations within one region.

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In theSaimiri sciureusmonkey, erythrocytes infected with the varO antigenic variant of thePlasmodium falciparumPalo Alto 89F5 clone bind uninfected red blood cells (rosetting), form autoagglutinates, and have a high multiplication rate, three phenotypic characteristics that are associated with severe malaria in human patients. We report here that varO parasites express avargene having the characteristics of group Avargenes, and we show that the varO Duffy binding-like 1α1(DBL1α1) domain is implicated in the rosetting of bothS. sciureusand human erythrocytes. The soluble varO N-terminal sequence (NTS)-DBL1α1recombinant domain, produced in a baculovirus-insect cell system, induced high titers of antibodies that reacted with varO-infected red blood cells and disrupted varO rosettes. varO parasites were culture adapted in vitro using human erythrocytes. They formed rosettes and autoagglutinates, and they had the same surface serotype and expressed the samevarOgene as the monkey-propagated parasites. To develop an in vitro model with highly homogeneous varO parasites, rosette purification was combined with positive selection by panning with a varO NTS-DBL1α1-specific mouse monoclonal antibody. The single-variant, clonal parasites were used to analyze seroprevalence for varO at the village level in a setting where malaria is holoendemic (Dielmo, Senegal). We found 93.6% (95% confidence interval, 89.7 to 96.4%) seroprevalence for varO surface-reacting antibodies and 86.7% (95% confidence interval, 82.8 to 91.6%) seroprevalence for the recombinant NTS-DBL1α1domain, and virtually all permanent residents had seroconverted by the age of 5 years. These data imply that the varO model is a relevant in vivo and in vitro model for rosetting and autoagglutination that can be used for rational development of vaccine candidates and therapeutic strategies aimed at preventing malaria pathology.