Sendai virus infected cells are readily cytolysed by guinea-pig complement without antibody

HeLa cells infected with Sendai virus (SV) acquired the ability to activate the alternative pathway (AP) of guinea-pig complement without antibody reaction. For induction of complement activating ability (CAA), at least 2 hr incubation of the infected cells was required. However, ultraviolet (UV)-irradiation (8400 erg/mm2) of SV did not impair the inducibility of CAA and 51Cr-labelled HeLa cells infected with UV-irradiated SV (UV-SV) became readily cytolysed by C4-deficient guinea-pig complement without antigen-antibody reaction. This phenomenon may represent a primary in vivo defence mechanism against SV infection by eliminating the virus-infected cells via activation of complement on the cell surface. Although SV-infected HeLa cells activated the AP of guinea-pig complement, they did not activate the AP of human or mouse complement. The species restriction in the CAA induced by SV infection may result in different pathological manifestations in virus-infected animals and may affect their susceptibility to this type of infection.