Comparative specificity and sensitivity of NS1-based serological assays for the detection of flavivirus immune response

Abstract

Flaviviruses are relevant animal and human pathogens of increasing importance worldwide. The similarities of the initial clinical symptoms and the serological cross-reactivity of viral structural antigens make a laboratory diagnosis of flavivirus infection problematic. The main aim of the present study was the comparative specificity and sensitivity analysis of the non-structural protein NS1 as an antigen to detect flavivirus antibodies in sera from exposed individuals. A strategy for the purification of native recombinant non-structural protein 1 of representative flaviviruses including tick-borne encephalitis, West Nile, Zika and dengue virus was developed. The immunological properties of the purified antigens were analyzed using sera of immunized mice and of infected individuals in comparison with standard commercial assays. Recombinant NS1 protein was confirmed as a valuable option for the detection of flavivirus antibodies with reduced cross-reactivity and high sensitivity offering additional advantages for the detection of vaccine breakthrough cases.

Author summary

Viruses transmitted by mosquitoes or ticks are on the rise worldwide and may cause life-threatening symptoms, such as brain damage or excessive bleeding. In recent years we experienced several epidemic threats caused by colonization of new geographic areas by the infected vector with large numbers of naive population at risk of infection. Furthermore, increased travel contributed to a rise of imported infections in non-endemic countries. Reliable diagnostics for these viruses have therefore become a pressing need. Serology of infection is complicated by a high level of cross reactivity among structural virion proteins that are generally used as antigens. Therefore, use of the viral non-structural protein NS1 secreted by Flaviviruses, a family of highly significant vector borne viruses that include that infectious cause of Zika, Dengue, west Nile fever and Tick-borne encephalitis, has been proposed as a more specific antigen for detecting specific immune responses. In this work NS1 from representative Flaviviruses were purified from mammalian cells to maintain full antigenic potential and used in serological assays in a comparative analysis with commercial assays. Results showed a high level of specificity and sensitivity of NS1-based assays that can be proposed in a variety of diagnostic formats, from standard assays to multiparametric portable devices for rapid deployment.