DENV type 4 NS1 (50 kDa)

Dengue fever can be caused by one of four distinct dengue virus (DENV) serotypes that cocirculate in many parts of the world. Point of care serotype-specific nonstructural protein-1 (NS1) capture assays for the rapid serotyping of DENV in human sera would greatly support epidemiological surveillance and potentially also prognosis in individual patients. To ensure both serotype specificity and broad coverage of variants within serotypes, we have applied an innovative approach for the generation and selection of serotype-specific anti-NS1 mAbs. To elicit mAbs against conformational epitopes, NMRI mice were immunized with living HEK 293 transfectants expressing the native target Ags in multiple display on the cell surface. For each serotype, three different NS1 sequence variants were sequentially used for immunization of mice, hybridoma selection, and capture assay development, respectively. Selection of optimal combinations of capturing and detecting mAbs yielded highly sensitive and specific NS1 serotyping ELISAs (st-ELISAs) for the four serotypes. st-ELISA testing of 41 dengue patient sera showed a 100% concordance with the serotype determined by serotype-specific reverse transcriptase real-time quantitative PCR. The respective NS1 variants could be detected for similar to 10 d after the onset of illness. Ab-dependent enhancement of DENV infections may be associated with a specific range of pre-existing anti-DENV serological Ab titers. Testing of patient sera with the developed st-ELISAs will not only be useful for epidemiological studies and surveillance, but it may also help to develop and validate assays that can distinguish protective versus enhancing Ab responses for risk assessment for the development of severe dengue disease in individual patients.

Zika virus (ZIKV) infection has been linked to congenital defects in fetuses and infants, as exemplified by the microcephaly epidemic in Brazil. Given the overlapping presence of Dengue virus (DENV) in the majority of ZIKV epidemic regions, advanced diagnostic approaches need to be evaluated to establish the role of pre-existing DENV immunity in ZIKV infection. From 2015 to 2017, five pregnant women with suspected ZIKV infection were investigated in Pavia, Italy. Among the five pregnant women, three were DENV-ZIKV immunologically cross-reactive, and two were DENV-naive. Advanced diagnosis included the following: (i) NS1 blockade-of-binding (BOB) ELISA assay for ZIKV specific antibodies and (ii) ELISpot assay for the quantification of effector memory T cells for DENV and ZIKV. These novel assays allowed to distinguish between related flavivirus infections. The three DENV-experienced mothers did not transmit ZIKV to the fetus, while the two DENV-naive mothers transmitted ZIKV to the fetus. Pre-existing immunity in DENV experienced mothers might play a role in cross-protection.