Effective host response to Francisella tularensis requires functional mast cells.

Evaluation of: Ketavarapu JM, Rodriguez AR, Yu J et al.: Mast cells inhibit intramacrophage Francisella tularensis replication via contact and secreted products including IL-4. Proc. Natl Acad. Sci. USA 105(27), 9313-9318 (2008). The intracellular pathogen Francisella tularensis is a highly infectious organism that infects cells of the immune system. Mast cells have been known for their role in anaphylaxis, although they are also important for their ability to aid in the defense against pathogens. The report by Ketavarapu et al. has demonstrated that mast cells function to limit the replication of F. tularensis live vaccine strain within macrophages in vitro as well as in vivo. It was determined that IL-4 is one secreted mediator of this effect thus highlights a previously unknown mechanism of host defense against F. tularensis.