Immunoreactivity and protective effects in mice of a recombinant dengue 2 Tonga virus NS1 protein produced in a baculovirus expression system.

The double-stranded replicative form of dengue 2 virus (DEN-2) RNA (Tonga strain) was used as a substrate to produce DNA clones of the NS1-NS2A genes via reverse transcriptase synthesis of full length cDNA followed by polymerase chain reaction amplification of the NS1-NS2A region. Products were cloned into pTZ18R for sequencing and into baculovirus for expression studies. The deduced amino acid sequence of the NS1-NS2A was almost identical to that of the S1 attenuated strain of DEN-2 Puerto Rico 159, differing in only four amino acids. The NS1 protein expressed in insect cells [Spodoptera frugiperda (Sf-9)] from the baculovirus recombinant was indistinguishable from authentic NS1 of DEN-infected Aedes albopictus cells in glycosylation, dimerization, cellular presentation and antigenicity. Mice injected with the expressed protein developed NS1-specific complement-fixing antibodies and were partially protected against neurological residua after intracranial challenge. The protective effect was mouse strain- and gender-specific.