Effector-triggered immunity against Legionella pneumophila in dendritic cells

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Project Summary Intracellular bacterial pathogens such as Legionella pneumophila, the causative agent of the severe pneumonia Legionnaires' disease, are responsible for significant disease burden in the United States every year. The growing use of immunosuppressive drugs, particularly TNF blockrs, to treat autoimmune diseases comes with a significantly increased risk of infection by intracellular bacterial pathogens, including Mycobacterium tuberculosis and Legionella pneumophila. The increasing numbers of individuals who are functionally immunocompromised due to growing use of TNF blockade, combined with the growing spread of antibiotic resistance, poses a serious public health concern. Our goal is to define the mechanisms by which TNF promotes immune defense against Legionella pneumophila. This information may enable development of targeted therapeutics that promote anti- bacterial defense in immunocompromised individuals. Critically, in new preliminary studies that take advantage of our ability to dissect the interactions between Legionella and dendritic cells, we find that TNF signaling drives a Legionella effector-triggered immune response that induces apoptosis in dendritic cells, thereby restricting intracellular Legionella replication. The proposed studies will provide fundamental insight into how TNF-mediated effector-triggered immunity promotes control of intracellular Legionella replication within dendritic cells. This information may provide a basis for the development of improved therapeutics for the treatment of Legionella and other bacterial pathogens.