Reassessing Legionella pneumophila Recognition during Intracellular Infection of Human Macrophages

Project: Research project

Project Details


Legionella pneumophila (Lp) causes Legionnaires' disease. Upon inhalation, Lp infects macrophages in the lung, and this is followed by severe inflammation. During infection of macrophages, Lp triggers the secretion of pro-inflammatory cytokines. Based largely upon studies done in murine models, the immune recognition of Lp is triggered by certain surface and endosomal Toll-like receptors (TLRs), cytosolic NOD-like receptors, RIG-I-like receptors, and inflammasomes. Recently, in order to discern the effect of Lp type II protein secretion on cytokine elicitation, we used shRNA to generate a panel of human macrophages that are deficient in individual immune components. While utilizing these new reagents, we made a number of observations concerning the recognition of Lp by human macrophages that deviate from / expand upon results obtained with murine cells. These findings include i) a minimal (rather than major) role for MyD88-dependent TLR signaling, ii) a larger role for the TRIF and TRAM adaptors and by extension endosomal TLR3 and/or endosomal TLR4, iii) a major role for the TBK-1 adapter, cGAS and STING, and by inference cytosolic DNA-sensing, and iv) a new role for PKR and likely other cytosolic RNA-sensors. These data call into question the field’s long-standing reliance on murine models and indicate a compelling need to further define the innate immune response in human macrophage models. Also, some of our results echo findings from human epidemiological studies that have been largely ignored in recent years. Therefore, we propose to utilize knockdown protocols to discern, in the context of Lp infection of human macrophages (both U937 cell lines and those derived from peripheral blood mononuclear cells), the relative importance of TLR3 and TLR4, cytosolic DNA sensors DDX41, DNA-PK, IFI16, and MRE11, and cytosolic RNA sensors DDX3, DHX9, DHX33, DDX1/DDX21/DHX36. In order to ensure an unbiased investigation of Lp recognition by human macrophages, we wi
Effective start/end date11/15/1810/31/21


  • National Institute of Allergy and Infectious Diseases (5R21AI137458-02)


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