Studies on the neutralization of herpes simplex virus. VI. The mode of action of complement upon antibodysensitized virus

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.

Familial herpes simplex infection associated with activation of the complement system

A patient with severe recurrent herpes infection was evaluated for immunologic analysis including a profile of complement components. The peripheral blood lymphocytes from the patient responded by proliferation to herpes simplex antigen but failed to produce leukocyte migration inhibition factor. Herpes simplex antibody titers increased during active infection. Total hemolytic complement (TCH50), the third (C3), fifth (C5), sixth (C6) and seventh (C7) components of complement, and factor B were dramatically reduced; the first (C1), second (C2) and fourth (C4) components of complement were within normal limits. In family members with a history of recurrent herpes simplex, one or more of the later complement components (C5, C6 or C7) was reduced. This study demonstrates the activation of complement in these serums via the alternative pathway.

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.

Studies on the neutralization of herpes simplex virus. VIII. Significance of viral sensitization for inactivation by complement

Early and late IgG of rabbits immunized with herpes virus showed, respectively, 8-fold and 2-fold enhancement of neutralization endpoint in the presence of complement (C). Kinetic curve experiments employing an appropriate amount of virus revealed that both neutralization and sensitization followed first-order reaction, and each IgG possessed a certain range of concentration where neutralization was negligible while sensitization was marked. Dose responses of neutralization and sensitization velocities demonstrated that the C enhancement of late IgG was about 7-fold and that of early IgG more than 20-fold. These facts suggested that the IgGs contained two different entities of complement-requiring (CRN) and non-requiring neutralizing (N) antibodies at different proportions, only the former being responsible for sensitization. The different CRN: N ratios obtained by the endpoint and kinetic methods may mean either that the two antibodies differ in avidity for the virus or that the number of critical sites per virion for CRN antibody is greater than that for N antibody. In this interpretation, sensitization by CRN antibody as well as neutralization by N antibody is thought to result from attachment of a single antibody molecule to the viral critical site. Alternative explanations, ascribing the mechanism of neutralization to steric hindrance of critical sites or to multiple hit of those sites by antibody, were denied by analyses of the present data.