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Infection and Immunity, December 2007, p. 5993-6007, Vol. 75, No. 12
0019-9567/07/$08.00+0     doi:10.1128/IAI.00695-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Chicken Cecum Immune Response to Salmonella enterica Serovars of Different Levels of Invasiveness

Friedrich-Loeffler-Institute, Institute of Molecular Pathogenesis,¹ Institute of Bacterial Infections and Zoonoses, Naumburger Strasse 96a, D-07743 Jena, Germany²

Received 23 May 2007/ Returned for modification 6 July 2007/ Accepted 26 July 2007

Day-old chicks are very susceptible to infections with Salmonella enterica subspecies. The gut mucosa is the initial site of host invasion and provides the first line of defense against the bacteria. To study the potential of different S. enterica serovars to invade the gut mucosa and trigger an immune response, day-old chicks were infected orally with Salmonella enterica serovar Enteritidis, S. enterica serovar Typhimurium, S. enterica serovar Hadar, or S. enterica serovar Infantis, respectively. The localization of Salmonella organisms in gut mucosa and the number of immune cells in cecum were determined by immunohistochemistry in the period between 4 h and 9 days after infection. Using quantitative real-time reverse transcription (RT)-PCR, mRNA expression of various cytokines, chemokines, and inducible nitric oxide synthase (iNOS) was examined in cecum. As a result, all S. enterica serovars were able to infect epithelial cells and the lamina propria. Notably, serovar Enteritidis showed the highest invasiveness of lamina propria tissue, whereas serovars Typhimurium and Hadar displayed moderate invasiveness and serovar Infantis hardly any invasion capabilities. Only a limited number of bacteria of all serovars were found within intestinal macrophages. Elevated numbers of granulocytes, CD8⁺ cells, and TCR1⁺ cells and mRNA expression rates for interleukin 12 (IL-12), IL-18, tumor necrosis factor alpha factor, and iNOS in cecum correlated well with the invasiveness of serovars in the lamina propria. In contrast, changes in numbers of TCR2⁺ and CD4⁺ cells and IL-2 mRNA expression seemed to be more dependent on infection of epithelial cells. The data indicate that the capability of Salmonella serovars to enter the cecal mucosa and invade lower regions affects both the level and character of the immune response in tissue.

Published ahead of print on 20 August 2007.

Editor: F. C. Fang