Monocytes internalize nanoparticles via macropinocytosis while B and T cell associate externally.

<p>(<b>a</b>) Representative flow cytometry plots of <i>in vivo</i> NP-Dy649⁺ uptake kinetics after intradermal administration: monocytes (CD11b⁺GR1^midSSC^lowF4/80⁺) and B cells (B220⁺) in the spleen. (<b>b</b>) Characteristic flow cytometry plots of biotinylated nanoparticle (NP-biotin) association with splenic (B, CD4, and CD8 cells) and bone marrow (CD11b⁺Ly6c⁺ and CD11b⁺Ly6g⁺) cells after 12 h incubation <i>in vitro</i>. To distinguish surface-associated- from internalized-NPs, cells were incubated before permeabilization with streptavidin-A488 (for extracellular association) and after permeabilization with streptavidin-A647 (for intracellular uptake). (<b>c</b>) Percentage of fluorescently labeled NPs (NP-Dy649) taken up by bone marrow cells as a function of the PI3K inhibitor (Ly294002) concentration. Bone marrow cells were incubated with increasing concentrations of Ly294002 (maximum 50 µM) for 45′ prior to the addition of NP-Dy649 for 12 h. Cells were subsequently stained and analyzed by flow cytometry. Open circles: CD11b⁺Ly6c⁺, filled squares: CD11b⁺Ly6g⁺, continuous line: vehicle control (VH, DMSO) for CD11b⁺Ly6c⁺, dashed line: VH for CD11b⁺Ly6g⁺.