The Birc1e cytosolic pattern-recognition receptor contributes to the detection and control of Legionella pneumophila infection

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Abstract
Baculovirus inhibitor of apoptosis repeat-containing 1 (Birc1) proteins have homology to several germline-encoded receptors of the innate immune system. However, their function in immune surveillance is not clear. Here we describe a Birc1e-dependent signaling pathway that restricted replication of the intracellular pathogen Legionella pneumophila in mouse macrophages. Translocation of bacterial products into host-cell cytosol was essential for Birc1e-mediated control of bacterial replication. Caspase-1 was required for Birc1e-dependent antibacterial responses ex vivo in macrophages and in a mouse model of Legionnaires' disease. The interleukin 1β converting enzyme–protease-activating factor was necessary for L. pneumophila growth restriction, but interleukin 1β was not required. These results establish Birc1e as a nucleotide-binding oligomerization–leucine-rich repeat protein involved in the detection and control of intracellular L. pneumophila.