Immunization with solid matrix-antibody-antigen complexes containing surface or internal virus structural proteins protects mice from infection with the paramyxovirus, simian virus 5.

A mouse model system has been developed to examine the ability of purified virus proteins to protect mice from infection with the paramyxovirus simian virus 5. The system is based on the infection of mouse lungs by intranasal administration of infectious virus. The relative amounts of virus proteins and nucleic acid present within infected lungs were estimated either by Western blot analysis of disrupted lung tissues or by in situ hybridization studies using cryostat sections of infected lungs. During a normal time course of infection in non-immunized mice increasing amounts of virus protein and nucleic acid were detected in the lungs until 3 days post-infection (p.i.). Thereafter the amount of virus present within the lungs remained relatively constant until 7 days p.i. when there was a rapid decrease. Cytotoxic T cells, but not neutralizing antibody, could be detected at the time when the amount of virus within the lungs was decreasing. Prior immunization of mice with solid matrix-antibody-antigen (SMAA) complexes containing either surface or internal virus structural proteins reduced the amount of virus replication within infected lungs, the greatest degree of protection being observed when nucleoprotein or matrix protein was used to immunize the mice. There was no correlation between the degree of protection observed and the level of neutralizing antibody present in immunized animals; no neutralizing antibody was detected in mice immunized with internal virus proteins even at the time of sacrifice 5 days p.i. We have previously shown that immunization of mice with SMAA complexes containing either surface or internal virus structural proteins can induce cytotoxic T cells and thus conclude that the most likely explanation for the protection observed in immunized mice is through the induction of cytotoxic T cells.