An interaction of Zika virus envelope fragments with serum antibodies derived from subjects after flavivirus infections

The causative agent of Zika fever (ZIKV) belongs to the genus Flavivirus of the family Flaviviridae. The flavivirus genus consists of more than 70 members. Based on virion structural organization and amino acid composition of proteins, this virus resembles other flaviviruses such as dengue (DENV), yellow fever and West Nile (WNV) posing a threat to human health. ZIKV is an arbovirus and may be transmitted by diverse mosquito species of the genus Aedes. It is believed that the main carriers are also able to transmit dengue virus, yellow fever virus as well as other flavivirus infections. In 1947, ZIKV was isolated for the first time from blood samples obtained from rhesus macaques inhabiting the Zika Forest (Uganda). Long time this virus was not considered as a dangerous to human pathogen, as Zika fever mostly occurs asymptomatically. However, analysis of Zika fever course in pregnant women unveiled a link between this disease and severe congenital disorders of the nervous system, including microcephaly, that allowed to deal with it as a dangerous infection thereafter. Rapid ZIKV spread outlined a number of problems faced by medical doctors, among which the main issue was the lack of assays for its virus-specific diagnostics. ZIKV displays a marked antigenic similarity with other flaviviruses. The majority of dengue-specific monoclonal antibodies binds to Zika virus. It is expected given the high degree of amino acid sequence similarity found for flavivirus polyprotein. Several antigens bearing ZIKV E surface protein fragments were constructed to assess an opportunity for conducting differential diagnostics for distinct flaviviruses based on detection of virus-specific antibodies. Vector plasmid pET32 was selected for producing recombinant antigens in E. coli cells. After creating constructs encoding the ZEa187 and ZEa40 proteins, the chimeric proteins were produced in amount necessary for performing ELISA with blood serum samples. Protein samples were prepared by isolating them from bacterial biomass via lysis followed by chromatographic purification. Blood sera obtained from human subjects recovered after Zika, Dengue and West Nile fevers were used to examined immunochemical properties of chimeric proteins. Human sera containing no antibodies against flavivirus types were used as a negative control. It was found that serum IgM class antibodies derived from patients with flavivirus infections demonstrated a high level of cross-reactivity by interacting with ZEa187 and ZEa40. Upon that, despite increment of mean specific interaction signal observed for such proteins and IgG of ZIKV sera, a marked cross-reactivity with the IgG of WNV and DENV sera was found. Thus, with some certainty it may be concluded that in immunochemical assays use of natural amino acid sequence specific to Zika virus surface protein as antigenic material does not allow to achieve high specificity for antibody detection.