Measurement of virus antigens on the surface of HeLa cells persistently infected with wild type and vaccine strains of measles virus by radioimmune assay.

Persistent states of measles virus infection have been established in HeLa cells by using Edmonston strain virus and two types of measles virus vaccine (M-VAC and Schwarz). The absolute amount of surface viral antigens expressed on these cells infected separately with the three viruses has been assessed by a newly developed method which employs [125I]-labelled Fab fragments of immunoglobulin G (IgG) from immune human sera. This method was used to determine the level of viral antigenic expression on acutely infected HeLa cells harvested at a time when 95 to 100% of cells could be lysed by antiviral antibody and complement. From our data, more than 1 X 10(6) antibody molecules must bind to each cell infected with measles virus before complement dependent lysis can occur in a homologous test system. Persistently infected cells bind 2 to 3 times less antibody than acutely infected cells and correspondingly exhibit less susceptibility to humorally-mediated immune lysis.