Recombinant RuV E2 Protein

The envelope glycoproteins E1 and E2 of rubella virus (RV) were engineered to display the FLAG epitope tag and a polyhistidine tag, at their amino and carboxy termini, respectively. These modified envelope proteins were produced in Sf9 insect cells utilizing baculovirus expression vectors, the E1 and E2 vectors giving rise to protein products of about 58 and 42 kDa, respectively. The recombinant proteins were purified by immobilized metal-ion affinity chromatography and reconstituted into liposomes via their hydrophobic transmembrane anchors. The liposomes were prepared by detergent dialysis in the presence of europium-DTPA chelate, enabling the subsequent measurement of the binding of the resultant proteoliposomes to the antibodies by time resolved fluorescence. RV mimicking proteoliposomes were recognized by antibodies specific for the E1 and E2 proteins, as well as the FLAG epitope tag. This type of virosome may prove useful for studies on the basic biological events of an RV infection or as diagnostic reagents. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

In an attempt to define diagnostic criteria that may help to distinguish the congenital rubella syndrome (CRS) from subclinical intrauterine rubella virus (RV) infection, maternal and fetal serum samples were analyzed using (1) enzyme immunoassay employing RV synthetic peptides as antigen, (2) IgG avidity assay, and (3) immunoblot under nonreducing conditions, in addition to hemagglutination inhibition and commercial enzyme immunoassays. Infants born with CRS and their mothers were shown to reveal low or undetectable levels of E2-specific antibodies and deficient IgG recognizing the major neutralizing antibody-inducing epitope on the E1 protein (SP15). Antibody responses were normal in mothers with presumed RV reinfection as well as in asymptomatic infants born after maternal primary rubella. The results indicate that the maturation of specific humoral immune responses is obviously less efficient when intrauterine RV infection results in CRS. The detection of high avidity IgG, conformational E2-specific as well as SP15-reactive antibodies may serve as a potential predictor for a benign outcome of intrauterine RV infections.