Amplifying Immunity

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Science  28 Feb 2014:
Vol. 343, Issue 6174, pp. 950
DOI: 10.1126/science.343.6174.950-b

Antigen-specific T cells are important for the control and clearance of many types of infection. T cells that do not recognize the specific pathogen, however, often participate in getting rid of infections, but the specific mechanisms that regulate the activation of these so-called “bystander” T cells are less well understood. O'Donnell et al. used mice infected with Salmonella to better understand this phenomenon and found that detection of microbe-associated molecular patterns by Toll-like receptor 4 and components of the inflammasome in a T cell extrinsic pathway led to the production of several cytokines, including interleukin 18 (IL-18). IL-18 in turn acted on bystander CD4+ T cells to amplify their antibacterial responses. In fact, mice in which the bystander activation of CD4+ T cells was inhibited were impaired in their ability to control Salmonella infection. Although not formally demonstrated, this may be a way for the immune system to avoid being overwhelmed by a rapidly dividing pathogen and/or to protect the host against co-infection.

Immunity 10.1016/j.immuni.2013.12.013 (2014).

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