We utilize the intracellular bacterial pathogen Legionella pneumophila, causative agent of the severe pneumonia Legionnaires' disease, as our primary model. Legionella has evolved numerous mechanisms for modulating eukaryotic processes in order to survive and replicate within host cells. The ease with which Legionella can be genetically manipulated provides a powerful system for dissecting immune responses to bacteria that differ in defined virulence properties and for elucidating mechanisms of bacterial pathogenesis.

We recently found that infected macrophages circumvent Legionella's ability to block host translation by selectively synthesizing and releasing key cytokines. These cytokines then instruct bystander immune cells to generate an effective immune response. We are defining additional mechanisms that facilitate communication between infected and bystander cells and promote antimicrobial defense.

One key immune pathway involves the inflammasome, a multi-protein cytosolic complex that activates the host proteases caspase-1 and caspase-11 upon cytosolic detection of bacterial products. These caspases mediate the release of IL-1 family cytokines and other inflammatory factors critical for host defense, but overexuberant activation can lead to pathological outcomes such as septic shock. We are currently pursuing how mouse and human inflammasomes differentially respond to bacterial infection.

Insight into these areas will advance our understanding of bacterial pathogenesis, how the innate immune system distinguishes between virulent and avirulent bacteria and initiates antimicrobial immunity, and will ultimately aid in the design of effective antimicrobial therapies and vaccines.