ER-Coordinated Activities of Rab22a and Rab5a Drive Phagosomal Compaction and Intracellular Processing of Borrelia burgdorferi by Macrophages

• Rab22a is an early regulator of borreliae phagocytosis, preceding Rab5a
• Compaction of borreliae in phagosomes is driven by membrane tubulation
• The ER coordinates Rab22a and Rab5a activities
• Rab22a and Rab5a regulate intracellular survival of borreliae

SummaryBorrelia burgdorferi is the causative agent of Lyme disease, a multisystemic disorder affecting the skin, joints, and nervous system. Macrophages and dendritic cells counteract Borrelia dissemination through internalization and degradation of spirochetes. We now show that Borrelia internalization by primary human macrophages involves uptake and compaction into Rab22a-positive phagosomes that are in close contact with Rab5a-positive vesicles. Compaction of borreliae involves membrane extrusion from phagosomes, is driven by Rab22a and Rab5a activity, and is coordinated by ER tubules forming contact sites of Rab22a phagosomes with Rab5a vesicles. Importantly, Rab22a and Rab5a depletion leads to reduced localization to lysosomes and to increased intracellular survival of spirochetes. These data show that Rab22a- and Rab5a-driven phagosomal uptake is a crucial step in the vesicular cascade that leads to elimination of spirochetes by macrophages. Rab22a and Rab5a thus present as potential molecular targets for the modulation of intracellular processing of borreliae in human immune cells.

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