Aggregatibacter actinomycetemcomitans LtxA Hijacks Endocytic Trafficking Pathways in Human Lymphocytes

Area of Science:

• Microbiology
• Cell Biology
• Immunology

Background:

• Leukotoxin (LtxA) from *Aggregatibacter actinomycetemcomitans* damages host cells.
• LtxA internalization by leukocytes expressing LFA-1 leads to cell death.
• The intracellular trafficking and localization of LtxA remain poorly understood.

Purpose of the Study:

• To investigate the intracellular trafficking pathways of LtxA in human T lymphocytes.
• To determine the role of endosomal trafficking in LtxA-mediated cytotoxicity.
• To characterize the pore-forming activity of LtxA at different pH levels.

Main Methods:

• Multi-fluor confocal imaging and flow cytometry in Jurkat T cells.
• Rab5a knockdown to assess the role of endocytosis.
• Planar lipid bilayer experiments to analyze LtxA pore formation at varying pH.
• Co-localization studies with endosomal and lysosomal markers (Rab5, Rab11A, Rab7, Lamp1) and CD11a.

Main Results:

• LtxA/LFA-1 complex enters Jurkat cells cytosol via dynamin-dependent, clathrin-independent pathways without plasma membrane damage.
• LtxA follows LFA-1 endocytic trafficking, co-localizing with endosomal/lysosomal markers.
• Rab5a knockdown significantly reduced Jurkat cell susceptibility to LtxA, implicating endocytic trafficking in toxicity.
• LtxA forms pores at acidic pH, potentially permeabilizing endosomal/lysosomal membranes.

Conclusions:

• LtxA internalization and subsequent endocytic trafficking are crucial for its cytotoxic effects.
• The degradative endocytic pathway, potentially involving lysosomes or Rab11A-recycling endosomes, is implicated in LtxA's mechanism of action.
• LtxA's pH-dependent pore-forming ability may contribute to lysosomal membrane permeabilization and cell death.