Published online by Cambridge University Press: 15 May 2009
Photoinactivation of vaccinia virus sensitized by methylene blue had parameters similar to those observed with other viruses. Thus inactivation proceeded exponentially to completion, was irreversible, independent of temperature and the intensity of illumination. Inactivation was dependent on the dose of illumination and the concentrations of both methylene blue and hydrogen ions. The effects of pH appeared to be primarily concerned with the tenacity of dye-virus binding. Inactivation was inhibited by small amounts of nucleic acid but not by their bases or pentoses. Inactivation was only affected by the presence of extraneous protein in relatively high concentration: it was not affected by the enzymes catalase or peroxidase. Attempts to obtain direct chemical evidence of the participation of viral nucleic acid in photoinactivation were unsuccessful.
Recombination experiments strongly indicated the involvement of viral protein in photoinactivation. Immunogenicity was not impaired since good responses of neutralizing antibody were obtained in rabbits immunized with vaccines photoinactivated over a wide range of exposure times.