NF-kappaB translocation prevents host cell death after low-dose challenge by Legionella pneumophila

Area of Science:

• Microbiology
• Immunology
• Cell Biology

Background:

• Legionella pneumophila causes Legionnaires' disease by replicating within macrophages.
• The bacterial Dot/Icm type IV secretion system is crucial for vacuole formation and host cell manipulation.
• Host cell signaling pathways are significantly altered during L. pneumophila infection.

Purpose of the Study:

• To investigate the host cell response to L. pneumophila infection, focusing on signaling pathways.
• To elucidate the role of the Dot/Icm secretion system in modulating host cell gene expression.
• To determine the impact of NF-kappaB activation on host cell survival and bacterial replication.

Main Methods:

• Global microarray analysis of human macrophage-like U937 cells.
• Assessment of NF-kappaB nuclear localization in infected macrophages.
• Inhibition of NF-kappaB translocation and analysis of host cell death and bacterial replication.

Main Results:

• Dot/Icm-dependent upregulation of antiapoptotic genes controlled by NF-kappaB was observed.
• L. pneumophila induced Dot/Icm-dependent NF-kappaB nuclear localization, independent of MyD88 and Nod1 at low infection doses.
• Inhibition of NF-kappaB led to premature host cell death and reduced bacterial replication.

Conclusions:

• NF-kappaB activation and subsequent induction of antiapoptotic genes are critical for host cell survival during L. pneumophila infection.
• The Dot/Icm system plays a key role in manipulating host NF-kappaB signaling for bacterial benefit.
• Host cell responses differ significantly based on infection multiplicity, masking key bacterial virulence mechanisms at high doses.