Characterisation and analysis of the NS1 gene of tick-borne encephalitis virus
Tick-borne encephalitis virus (TBEV) encodes a highly immunogenic ncnstructural glycoprotein, NS1. The proposed NS1 gene from the TE V strains Neudörfl and K23 was identified, cloned and sequenced. The NS1 gene from the Neudorfl strain of TBEV was then cloned under the powerful constitutive cytomegalovirus (CMV) major immediate-early promoter (IE) and the CMV IEP/NS1 fragment used as the basis of an adenovirus Eta deletion mutant. The novel combination of the cytomegalovirus immediate- early promoter and the adenovirus vector produced extremely high levels of NS1 expression in cells which do not support the replication of the adenovirus deletion mutant. The recombinant protein was shown to be indistinguishable from authentic TBEV NS1 in its (i) apparent molecular weight by polyacrylamide gel electrophoresis, (ii) glycosylation pattern, (iii) ability to form high molecular weight complexes, and (iv) ability to be secreted from cells. Furthermore, appropriate processing of NS1 expressed by the adenovirus recombinant occurred independently of any additional TBEVencoded gene function. When inoculated directly into mice, the recombinant adenovirus RAd51 was shown to elicit an antibody response to the TBEV NS1 antigen. Immunization of mice with RAd51 conferred both protection from disease and death when challenged with a lethal dose of TBEV. The capability of RAd51 to elicit an immune response following inoculation into mice was shown to result fron de novo synthesised NS1 and not co-inoculated NS1. It has been proposed that protection elicited against TBEV challenge by NS1 is due to complement mediated cytolysis of infected cells. The ability of NS1 to protect mice deficient in the terminal lytic pathway of the complement cascade, implied that complement mediated cytolysis is not the major mechanism by which protection is elicited. This research programme was carried out in collaboration with the Centre for Applied Microbiology and Research, Porton Down
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