Studies on the Neutralization of Herpes Simplex Virus

IX. Variance in Complement Requirement among IgG and IgM from Early and Late Sera under Different Sensitization Conditions

Abstract

Early and late sera of rabbits immunized with herpes simplex virus were fractionated into IgG and IgM, and the minimal concentration of complement (C) required for full enhancement of neutralizing activity was determined for each by the plaque reduction method. In tests employing simultaneous mixing of virus, antibody and C, C-requiring neutralizing (CRN) antibody in IgM required 2-8 times more C than that in IgG. When virus-antibody mixtures were incubated at 0 C overnight before addition of C, a marked enhancement of CRN endpoint especially of late IgG and IgM was exhibited, in contrast to materially unchanged titers of the ordinary neutralizing antibody. This result suggested an abundance of slow-reacting CRN-virus complexes. The CRN antibody so detected required about 4 times more C than that detectable by the usual test in the case of late IgG and IgM. When virus sensitized with late IgG at 0 C overnight was further incubated at 37 C for 1 hr, the C requirement changed but slightly without showing any more increase of the endpoint, whereas sensitization at 0 C for 2 to 3 days further increased the CRN antibody endpoint but the C requirement was equal to that after 1 day's sensitization at 0 C. Based on these and earlier findings, a hypothesis is proposed that binding of a single antibody molecule with virus may cause a series of changes of the virus particle or part of those changes depending on the nature of antibody and on the sensitization condition, and C added to such complexes at an appropriate stage of the changes can accelerate the procession of the changes leading eventually to inactivation.