Lipid microdomain-dependent macropinocytosis determines compartmentation of Afipia felis

Area of Science:

• Cell Biology
• Microbiology
• Immunology

Background:

• Phagocytic compartments typically mature into phagolysosomes for degradation.
• The pathogen Afipia felis resides in a unique compartment distinct from standard phagocytic organelles.

Purpose of the Study:

• To investigate the mechanism of Afipia felis internalization by macrophages.
• To understand the intracellular trafficking and phagosome development of Afipia felis.
• To identify factors influencing Afipia felis uptake and survival within macrophages.

Main Methods:

• Macrophage cultures treated with cholera toxin B subunit, cholesterol modifiers, or amiloride.
• Ultrastructural analysis of Afipia felis uptake.
• Opsonization of Afipia felis with monoclonal IgG antibodies.

Main Results:

• Afipia felis internalization and unusual phagosome development are reduced by disrupting macrophage lipid rafts (GM1 ganglioside) or plasma membrane cholesterol.
• Amiloride inhibits a late stage of macropinocytosis, crucial for Afipia felis uptake.
• Ultrastructural studies confirm Afipia felis is primarily taken up via macropinocytosis.
• Bacteria opsonized with IgG are ingested via Fcgamma receptors, leading to normal phagolysosome maturation.

Conclusions:

• The preferred uptake of Afipia felis relies on intact lipid microdomains and macropinocytosis, resulting in an atypical phagosome that promotes intracellular survival.
• Alternative uptake via Fcgamma receptors directs bacteria to a degradative pathway, unlike the preferred macropinocytic route.