Paradoxical Pro-inflammatory Responses by Human Macrophages to an Amoebae Host-Adapted Legionella Effector

Area of Science:

• Microbiology
• Cell Biology
• Immunology

Background:

• Legionella pneumophila naturally infects amoebae, but also causes pneumonia in humans by infecting alveolar macrophages.
• Understanding host-pathogen interactions is crucial for developing treatments against Legionella infections.

Purpose of the Study:

• To investigate the role of the effector protein LamA from Legionella pneumophila in host cell manipulation.
• To elucidate the mechanisms by which LamA affects both human macrophages and amoebae.

Main Methods:

• The study involved infecting human myeloid-differentiated macrophages (hMDMs) and amoebae with Legionella pneumophila.
• Researchers analyzed the effects of LamA injection on host cell metabolism, specifically glycogen degradation and glucose production.
• Bacterial proliferation and host immune responses, including M1-like differentiation and tryptophan degradation, were assessed.

Main Results:

• Legionella pneumophila injects LamA, an amylase, into host cells, degrading glycogen to produce hyper-glucose.
• In human macrophages, this triggers aerobic glycolysis, M1-like inflammation, and tryptophan degradation, modestly restricting bacterial growth.
• In amoebae, LamA disrupts glycogen availability, preventing cyst wall synthesis and hindering bacterial proliferation within the natural host.

Conclusions:

• LamA is an amoeba-adapted effector that subverts the natural host's encystation process.
• The pro-inflammatory response observed in human macrophages appears to be an unintended consequence of LamA's action, rather than a direct host-defense mechanism.