Development of uptake capacity and bactericidal activity in myeloid cells during GM-CSF-driven differentiation. (INC6P.326)

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Abstract The antigen presenting function of dendritic cells (DC) is well defined, yet their ability to handle bacterial infection is poorly understood. We have previously shown that GM-CSF-derived DC can confine Listeria monocytogenes (Lm) to the phagosome, preventing its invasion of the cytosol, growth, and spread. However, it is not clear at what stage of development DC acquire the capacity to retain Lm in the phagosome. To measure this activity at different stages of development, GM-CSF driven bone marrow cells were sorted based on expression of Ly6C, CD115, and CD11c. This strategy enables isolation of cells representing five distinct myeloid cell types: CMP, GMP, monocytes, inflammatory dendritic precursors (IDP), and inflammatory DC (IDC). To measure bacterial invasion of the cytosol, we used an Lm strain that expresses GFP upon cytoplasmic entry, in combination with fluorescent bioparticles to measure bulk uptake. The CMP demonstrated minimal uptake capacity and little bacterial cytoplasmic entry. The GMP population showed greatly increased uptake capacity, but also high susceptibility to bacterial cytoplasmic entry. In the monocyte population, the uptake capacity reached its peak, and these cells gained the capacity to confine the bacteria to the phagosome. Finally, the uptake capacity decreased modestly in the IDP and IDC populations, but these cells also blocked cytoplasmic invasion of the bacteria. The mechanistic basis of phagosomal retention was further examined.