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Infect. Immun., Apr 1996, 1154-1160, Vol 64, No. 4
C Chong, KL Bost and JD Clements
The use of attenuated Salmonella spp. as live oral vaccine carriers fo r
foreign antigens has been extensively studied. We have shown that
appropriately prepared nonviable organisms are as effective as viable
organisms in eliciting humoral immune responses against a foreign antigen
delivered by these vectors. It is not clear how strain viability affects
the development of a cell-mediated immune response. In the present study,
we demonstrate that BALB/c mice orally immunized with viable attenuated
Salmonella spp. were protected against subsequent challenge while animals
immunized with killed organisms were not. Protection was correlated with
increased production of interleukin- 12 (IL-12) p40 mRNA in the Peyer's
patches within hours of oral administration. Peritoneal macrophages from
lipopolysaccharide (LPS)- responsive and LPS-unresponsive mice were also
examined for production of IL-12 p40 mRNA following exposure to the viable
or killed attenuated Salmonella carrier. There was dramatic upregulation of
IL-12 p40 mRNA following exposure of macrophages to either viable or killed
organisms. By 4 h postexposure, viable organisms had induced a 27-fold
increase in IL-12 p40 mRNA levels while killed organisms had induced a
9-fold increase in IL-12 p40 mRNA levels. This was observed in macrophages
isolated from both LPS-responsive and unresponsive mice. The higher levels
of IL-12 induced by viable Salmonella spp. may result in the development of
a Th1 response and cell mediated immunity, while the lower levels of IL-12
induced by killed Salmonella spp. may not be sufficient to promote a Th1
response.
Copyright © 1996, American Society for Microbiology
Differential production of interleukin-12 mRNA by murine macrophages in response to viable or killed Salmonella spp
Department of Microbiology and Immunology, Tulane University Medical Center, New Orleans, Louisiana 70112, USA.
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