Salmonella sneaks past security

Certain gut cells can leave resident bacteria alone but respond selectively to invaders. Satoshi Uematsu, Shizuo Akira, and colleagues (Osaka University, Japan) suggest that gut cells achieve this differentiation by using a special, pathogen-specific receptor called the Toll-like receptor 5 (TLR5). But the pathogenic Salmonella typhimurium turns the situation around: events triggered by the special receptor help the bug to invade its host.

TLRs, which are expressed on professional antigen-presenting cells, recognize common pathogen-associated molecules and trigger innate immunity. TLR5 on dendritic cells recognizes bacterial flagellin protein in vitro, but its function in vivo was previously unknown.

Akira's team found that TLR5 mRNA was highly expressed in the mouse intestine particularly in a specific subpopulation of antigen-presenting lamina propria cells (CD11c⁺ LPCs). In these cells, TLR5 was necessary for bacterial...