Neutralization of measles virus infectivity and antibody-dependent cell-mediated cytotoxicity activity against an Epstein-Barr virus-infected cell line by intravenous immunoglobulin G [corrected]

Abstract

Patients with antibody deficiency disorders are highly susceptible to microbial infections. Intravenous (i.v.) immunoglobulin concentrates were originally developed as replacement therapy for such patients. The present study assesses the measles virus neutralizing antibody titers and the antibody-dependent cell-mediated cytotoxicity (ADCC) capacities against Epstein-Barr virus (EBV)-infected cells of immunoglobulin G (IgG) preparations produced for i.v. use (i.v. IgG). The level of neutralizing antibodies against measles virus was determined by a syncytium neutralization test with Vero cells as targets. The measles virus neutralizing antibody titers of the i.v. IgG preparations were >3 x 10(2) and were an average of 1.0 log higher than the titers in pooled plasma from healthy subjects. The two IgG preparations tested showed similar ADCC activities against EBV-infected Raji cells, being active at concentrations of 3 mg/ml or higher. i.v. IgG bound to Raji cells but not to the EBV-negative Ramos cells, as evaluated by flow cytometry. Our in vitro findings may provide further support for the use of i.v. IgG for the prevention and treatment of infections caused by specific viral pathogens.

FIG. 1.

ADCC activities against EBV-infected Raji cells provided by i.v. IgG preparations. The ADCC potentials of i.v. IgG and plasma samples against EBV-positive Raji cells and EBV-negative Ramos cells were tested. The mean ± SD percentage of specific cell death following incubation of the targets with blood lymphocytes is shown. The IgG concentrations in the i.v. IgG preparations and plasma samples are indicated. A plasma pool was prepared with plasma from 12 donors and had 8.611 g of IgG per liter. PBS and 5% sorbitol replaced i.v. IgGs in the samples. All experimental points were run in triplicate. The results of one representative experiment from a total of four that were conducted are shown. BRP with human IgGs was used as a control and was obtained from European Directorate for the Quality of Medicines.

FIG. 2.

i.v. IgG binds to Raji cells but not to Ramos cells. Cells were incubated with i.v. IgG or plasma and stained with anti-human IgG-FITC (top panels), anti-human IgM-FITC (bottom panels), or the isotype control mouse IgG1-FITC (gray shading). 2ry Ab, cells incubated only with the FITC-conjugated secondary antibody. The results presented here are representative of those from two identical experiments.

FIG. 3.

Syncytium formation in MV-infected Vero cells. Vero cells were infected with MV, and syncytium formation was observed 48 h postinfection (a). At higher magnification (b), multiple nuclei are visible inside syncytia (arrows). The results presented here are representative of those from five identical experiments.

FIG. 4.

Syncytium-neutralizing capacity of i.v. IgG. Vero cells were incubated with MV-specific i.v. IgGs or an MV-plasma cocktail in duplicate wells (24-well plates) for 1 h, as explained in Materials and Methods. Shown are the mean ± SD numbers of syncytia counted in independent wells of duplicate samples. PBS and sorbitol indicate Vero cells incubated with a cocktail of MV and PBS and 5% sorbitol, respectively. The results of one representative experiment of a total of four that were performed are shown. BRP with human IgGs was used as a control and was obtained from the European Directorate for the Quality of Medicines.