Different affinity of monoclonal antibodies for conserved neutralizing epitopes on two strains of rubella virus

Apoptosis induction by the infection with Gilchrist strain of rubella virus

Apoptosis is an active process of cellular self-destruction, which can be initiated in response to several stimuli such as toxic substances, hormones, cytokines, trophic or osmotic modifications and viral infections. In this study, we demonstrate that in vitro rubella-virus (RV) induced cell death exhibited properties of apoptosis, characterized by condensation and segmentation of nuclei and internucleosomal cleavage of nuclear DNA. Apoptosis was not seen in the cells absorbed with UV-inactivated virus, indicating that the viral replication is required for the induction of apoptosis. Our results suggest that most of the cells undergoing apoptosis are non-infected neighboring cells.

Evaluation of antibodies against a rubella virus neutralizing domain for determination of immune status

The protective immune responses against rubella virus (RV) are related to its neutralizing epitopes, an issue that is important to consider when assessing the immune status of patients with remote infection. In the present paper, we compare the antibodies detected by a synthetic-peptide-based enzyme immunoassay (EIA) with antibodies detected by the traditional technique of hemagglutination inhibition (HIA) in patients with remote RV infection. The synthetic peptide used as an antigen (SP15) represents a neutralizing epitope that corresponds to amino acids 208 to 239 of the E1 glycoprotein. The SP15-EIA was developed, all variables that affected the assay were standardized, and the test was validated using reference sera. Serum samples (n = 129) from patients with remote RV infection were tested by HIA and SP15-EIA. Discrepant sera were assayed by MEIA (IMX/Abbot). The comparison between HIA and SP15-EIA, taking HIA as the standard methodology for determining immune status, showed that SP15-EIA is very specific and sensitive for detecting protecting antibodies (specificity, 100%; sensitivity, 98.20%). This study demonstrates that antibodies against the neutralizing domain represented by SP15 would be important in the memory response after natural infection and may be a good tool in the determination of the true immune status of patients with remote infection with regard to RV.

Neutralizing monoclonal antibody to the E1 glycoprotein epitope of rubella virus mediates virus arrest in VERO cells

The best-known mechanism of action of antibody-mediated virus neutralization is to impede the entrance of viruses to host cells, as determined by neutralization assays. Antibodies may also inhibit the exit of rubella virus (RV) from infected host cells; in this case, the interaction of the antibodies with their domains must occur on the plasma membrane, because antibodies cannot enter the cells. In the present study, we were able to block temporally the exit of virions from RV-infected cells by the binding of monoclonal antibody (mAb) H3 to their surface. The objective was accomplished in three steps: first, we determined the duration of the viral replication cycle; then we established the kinetics of the presence of the domains defined by our mAbs in the cytoplasm of RV-infected VERO cells; and, finally, we assessed the release of viral particles to the supernatant of infected VERO cells in the presence or absence of mAbs or positive and negative mice sera. RV-specific mice sera and mAb H3, which binds to the amino acid sequence 208-239 of the RV-E1 glycoprotein, were able to delay for 24 hours the release of virions from infected cultures, suggesting that the reaction of mAb H3 with its epitope may arrest any change necessary for the assembly and/or release of virions. In conclusion, the neutralizing domain recognized by mAb induces antibodies that can block the viral replication by several mechanisms of action, such as the obstruction of virus entry into cells and the delay of viral release. All of these mechanisms are intimately involved in the critical virus-host cell interactions that allow self-limitation of the infection.

Presence of a neutralizing domain in isolates of rubella virus in Cordoba, Argentina

We studied the presence of a neutralizing epitope of rubella virus (RV) in locally circulating strains in Cordoba, Argentina, using binding by the monoclonal antibody (MAb) H3. This epitope is contained in a sequence of the E1 glycoprotein (E1208-239) represented by the synthetic peptide SP15. H3 MAb showed specific binding to SP15 by enzyme-linked immunosorbent assay (ELISA). One wild-type postnatal isolate, four clones derived from this isolate, and one congenital isolate were reactive with H3 by ELISA. These results suggest that the region of RV represented by SP15 is a domain present in locally circulating strains.