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Infect. Immun., Jan 1998, 224-231, Vol 66, No. 1
MG Covone, M Brocchi, E Palla, W Dias da Silveira, R Rappuoli and CL Galeotti
The effects of heterologous gene dosage as well as Salmonella typhimurium
strain variability on immune response toward both the heterologous antigen,
the nontoxic mutant of the Escherichia coli heat- labile enterotoxin LTK63,
and the carrier Salmonella strain have been analyzed. Effects of a single
integration into the host DNA and different-copy-number episomal vectors
were compared in S. typhimurium delta cya delta crp delta asd strains of
two different serotypes, UK-1 and SR-11. Expression of the enterotoxin in
the different Salmonella isolates in vitro was found to vary considerably
and, for the episomal vectors, to correlate with the plasmid copy number.
LTK63-specific serum immunoglobulin G (IgG) and mucosal immunoglobulin A
(IgA) antibodies were highest in mice immunized with the high-level-
expression strain. High anti-LTK63 IgG and IgA titers were found to
correspond to higher anti-Salmonella immunity, suggesting that LTK63 exerts
an adjuvant effect on response to the carrier. Statistically significant
differences in anti-LTK63 immune response were observed between groups of
mice immunized with the attenuated delta cya delta crp UK-1 and SR-11
derivatives producing the antigen at the same rate. These data indicate
that the same attenuation in S. typhimurium strains of different genetic
backgrounds can influence significantly the immune response toward the
heterologous antigen. Moreover, delivery of the LTK63 enterotoxin to the
immune system by attenuated S. typhimurium strains is effective only when
synthesis of the antigen is very high during the initial phase of invasion,
while persistence of the S. typhimurium strain in deep tissues has only
marginal influence.
Copyright © 1998, American Society for Microbiology
Levels of expression and immunogenicity of attenuated Salmonella enterica serovar typhimurium strains expressing Escherichia coli mutant heat-labile enterotoxin
Immunobiology Research Institute Siena, Department of Molecular Biology, Chiron Vaccines, Italy.
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