Studies on the nonneutralizable fraction of poliovirus

Neutralization activity of some Coxsackie B3 antibodies is compromised by protein factor(s) secreted by Vero cells

When various anti-Coxsackie B3 virus antibodies were examined for the neutralizing activity in cultures under liquid medium, some antibodies including monoclonal antibodies gave abnormally low titers in the neutralization test in Vero cells, in comparison with the other cells such as HeLa, FL, HEp-2, or primary monkey kidney cells. The neutralization titer of these antibodies was, however, similar in all these cells by plaque reduction assays under agar overlay, i.e., the above phenomenon was restricted to cultures under liquid medium. The reduced neutralization titer in Vero cells under liquid medium was found to be brought about by protease-sensitive factor(s) released by Vero cells, because (1) the addition of Vero cell culture fluid resulted in a marked reduction of neutralizing titer in primary monkey kidney cells, and (2) the activity of the Vero cell factor was destroyed by trypsin (20 micrograms/ml for 1 h). As three-day incubation of virus-antibody complex in Vero cell culture fluid resulted in a partial restoration of virus infectivity, the binding of antibody to virions appears to be competed by the Vero cell factor.

Monoclonal antibodies to the glycoprotein of vesicular stomatitis virus: comparative neutralizing activity

Nineteen independently isolated hybridomas producing monoclonal antibodies to the glycoprotein of vesicular stomatitis virus were isolated and studied for their capacity to neutralize viral infectivity. By measuring competitive binding of 125I-labeled monoclonal antibodies in a radioimmunoassay. 11 different, non-cross-reacting antigenic determinants were identified on the vesicular stomatitis virus G protein. All monoclonal antibodies reacting with determinants 1, 2, 3, and 4 resulted in viral neutralization, whereas those binding to the other seven determinants did not neutralize infectivity. The mixture of two monoclonal antibodies binding to different determinants resulted in a more rapid neutralization than either antibody alone, suggesting that different antibodies can exert a synergistic effect on viral neutralization. Kinetic experiments revealed biphasic neutralization curves similar to those expected for heterologous antibody. No evidence could be obtained to relate biphasic kinetics of viral neutralization to heterogeneous populations either of antibody molecules or of virus. The possible significance of the kinetic data with monoclonal antibodies is discussed.

Neutralization and sensitization of cytomegalovirus by IgG antibody, anti-IgG antibody, and complement

Human cytomegalovirus (CMV) strain Ad 169 was reacted with IgG antibody obtained from infected renal transplant patients, and the degree of neutralization was determined. The mixture of antibody and virus was then incubated with anti-human IgG (A-IgG) or complement (C) to measure additional neutralization by these agents and thus to estimate the concentration of infectious virus-antibody complexes which had been formed. Neutralization and formation of infectious complexes susceptible to neutralization by A-IgG or C decreased with lower concentrations of antibody. The rate of neutralization of preformed complexes by A-IgG or C was more rapid than the formation of complexes or the neutralization of native virus. If equally infectious suspensions of native virus and virus plus antibody were challenged with additional CMV antibody both solutions were neutralized to the same degree. The data are most compatible with the suggestion that the formation of infectious virus-antibody complexes is the initial step in the neutralization process. These complexes do not appear to be protected from further neutralization.

Neutralization of animal viruses

Various aspects of the interaction of bacterial viruses and antibody were studied by Andrewes and Elford in England. Similar studies, as well as studies on animal viruses, were carried out in Australia by Burnet and his colleagues. One result of their extensive studies, which were summarized in great detail, was the conclusion that, with respect to their interaction with antibody, bacterial and animal viruses were basically different. Specifically, the difference resided in the stability of the union of virus and antibody, whereas bacterial viruses formed stable complexes, animal viruses formed complexes that tended to dissociate readily. The introduction of animal cell cultures as host systems greatly aided in the study of animal viruses, with respect to fewer and more readily controlled variables, and by the use of the plaque assay in enhanced quantitative reliability. In 1956, Dulbecco et al. described the interaction of two animal viruses with their respective antibodies. The results of these studies led these investigators to conclude, among other things, that animal viruses, at least the two they studied, reacted with antibodies to form complexes that did not dissociate spontaneously. This interpretation was challenged by Fazekas de St. Groth and Reid. As more animal virus-antibody systems were studied by many investigators, there seemed to be a greater accord for irreversible, rather than reversible, interaction. For this reason, in this chapter it is assumed that there are no differences between bacterial viruses, as one category, and animal viruses, as a separate category, concerning their interaction with antibodies. Rather, differences, when they exist, are considered to be related to the viruses per se. Although this chapter is intended to survey the neutralization of animal viruses, occasional reference is made to the studies on bacterial viruses when these studies are pertinent and illuminating to the topic at hand.

Enhancement by diethylamineothyl-dextran of the plaque-forming activity of foot-and-mouth disease virus-antibody complexes in pig kidney IB-RS-2 cells

Mixtures of foot-and-mouth disease (FMD) virus and homologous antibody, assayed for surviving plaque-forming units (PFU) in pig kidney IB-RS-2 cells, demonstrated an average ten-fold greater recovery of infectivity when diethylaminoethyl-dextran (DEAE-dextran) was included in the overlay medium. This enhancement, which was not detected in baby hamster kidney BHK21 cells, was due to the ability of the polycation to potentiate attachment of virus-antibody complexes to the IB-RS-2 cells. In some instances the effect was so pronounced that the plaque-forming activity of virus in the presence of homologous antibody exceeded that of virus alone.