Role of Type 4B Secretion System Protein, IcmE, in the Pathogenesis of .

is an obligate intracellular Gram-negative bacterium that causes Q fever, a life-threatening zoonotic disease. replicates within an acidified parasitophorous vacuole derived from the host lysosome. The ability of to replicate and achieve successful intracellular life in the cell cytosol is vastly dependent on the Dot/Icm type 4B secretion system (T4SSB). Although several T4SSB effector proteins have been shown to be important for virulence and intracellular replication, the role of the icmE protein in the host- interaction has not been investigated. In this study, we generated a Nine Mile Phase II (NMII) mutant library and identified 146 transposon mutants with a single transposon insertion. Transposon mutagenesis screening revealed that disruption of gene resulted in the attenuation of NMII virulence in SCID mice. ELISA analysis indicated that the levels of pro-inflammatory cytokines, including interleukin-1β, IFN-γ, TNF-α, and IL-12p70, in serum from Tn::icmE mutant-infected SCID mice were significantly lower than those in serum from wild-type (WT) NMII-infected mice. Additionally, Tn::icmE mutant bacteria were unable to replicate in mouse bone marrow-derived macrophages (MBMDM) and human macrophage-like cells (THP-1). Immunoblotting results showed that the Tn::icmE mutant failed to activate inflammasome components such as IL-1β, caspase 1, and gasdermin-D in THP-1 macrophages. Collectively, these results suggest that the icmE protein may play a vital role in virulence, intracellular replication, and activation of inflammasome mediators during NMII infection.