Bacteria expressing invasion genes can penetrate the intestinal epithelial barrier only through cells located in Peyer's patches. But after oral administration Salmonella typhimurium bacteria deficient in invasion genes are still able to reach the spleen by an as yet unknown invasion route. In April Nature Immunology, researchers from the University of Milano-Bicocca report a mechanism that may be exploited by bacteria to spread throughout the body.

Maria Rescigno and colleagues infected murine intestinal segments either with non-pathogenic Escherichia coli expressing the red fluorescent protein (DsRed) or with a combination of unlabeled pathogenic Salmonella and DsRed-conjugated nonpathogenic E. coli. In both cases they found that dendritic cells from the epithelium take up bacteria directly. Dendritic cells open the tight junctions between epithelial cells, send dendrites outside the epithelium and directly sample bacteria (Nat Immun 2001, 2:361-367).

In addition, dendritic cells expressed the tight-junction proteins occludin, claudin 1...

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