Quantitation of antibodies to Herpes simplex virus types 1 and 2 by complement-dependent antibody lysis of infected cells

The release of 51Cr from cells infected with herpes simplex virus type 1 or type 2 by antibody and complement was examined as a method of quantitating antibodies to the viruses. With decreasing concentration of antibody, a typical dose-response curve was observed; a region of antibody excess in which dilution did not affect percentage of specific 51Cr release followed by a region in which a linear relation existed between dilution and percentage of specific 51Cr release. Therefore, a quantitative expression of antibody titer was defined as that dilution of serum which yielded 50% specific 51Cr release. The slopes of the linear portion of the dose-response curves were characteristic of the type of virus used to infect the cells and not upon the source of antiserum, thus, the slopes could be used to estimate antibody titers. The multiplicity of infection influenced the antibody titers; reproducible results were obtained when cultures were infected with 3 to 5 plaque-forming units per cell; the antibody titers decreased when less virus was used. The antibody titers obtained by the 51Cr release test were similar to those obtained by a microneutralization test. The 51Cr release test was found to be reproducible and to be useful in estimating the percentages of antibody activity attributable to antibodies to cross-reacting and type-specific antigens.