Analysis of complement-dependent antibody-mediated lysis of target cells acutely infected with measles

A sensitive assay for the detection of complement-dependent cytolytic measles-antibodies in monkey and human sera is described. The high sensitivity of the technique is dependent upon the use of Vero or MA-104 cells acutely infected with a high-titered, non-syncitiogenic strain of attenuated measles virus. Cytolytic antibody titers of serum can be determined either by endpoint dilution in the presence of a standard dilution of heterologous (guinea pig) complement or by percentage of lysis of a specific number of target cells at a standard dilution of immune serum (1:32). The latter technique proved expedient in the comparison of cytolytic activities of large numbers of serum samples. Clearly, the alternative complement pathway is effective in lysis of these cells, but neither the classical nor the alternative pathway alone appears to be as effective as both pathways combined. No prozone effect occurred with homologous complement, and inhibition of lysis was eliminated by washing sensitized cells before addition of heterologous complement. Lysis of measles-infected cells untreated with measles antibody occurred in the presence of both normal and C4-deficient guinea pig serum at high concentrations, but no such activity occurred with non-immune human or rhesus serum. Antibody-mediated complement-dependent lysis of measles-infected cells may be an important immune defense against acute measles infection.