Outbred mice were vaccinated with various artificial
Salmonella vaccines and subsequently challenged intraperitoneally with graded doses of virulent Salmonella typhimurium. The
Salmonella vaccines used were: (i) octasaccharide, obtained by hydrolysis of the O-antigenic
polysaccharide chain of S. typhimurium strain SH 4809 with phage P22-associated endo-rhamnosidase and covalently linked to either
diphtheria toxin or edestine; (ii) purified outer
membrane proteins (
porins) from S. typhimurium; and (iii) octasaccharide covalently linked to
porins. All
vaccines induced significant protection against experimental
infection of mice with S. typhimurium. However, vaccination with the octasaccharide-
porin conjugate resulted in better protection than that obtained by vaccination with octasaccharide or
porin vaccines separately. Rabbit
antibodies raised against the different
vaccines were also passively administered intravenously to mice. Such mice were protected against challenge with virulent S. typhimurium by
antibodies specific for the S. typhimurium
O-antigen or for the
porins. Thus, active immunization with more than one surface component of Salmonella bacteria improved the efficacy of the
vaccine. The data from the passive immunization experiments also emphasized the role of humoral immunity for protection against S. typhimurium
infection.