2.4. Cellular uptake study and mannose receptor blocking study

Cellular uptake was evaluated by fluorescence microscope (Olympus, Tokyo, Japan) and microplate system (CORONA, Tokyo, Japan) with FITC as a fluorescent marker. U937, M1, and M2 cells were seeded in six-well plates at a density of 10⁶ cells per well for 24 h. Dil at a concentration range of 10 μL/mL was added to these cells and stained for 10 minutes. Then, FITC-loaded MIC-NPs were added in the experimental group, and unloaded MIC-NPs were added in the control group. The mixtures were incubated in incubator at 37 °C under 5% CO₂ for 3 h. One milliliter of RPMI medium (1640, Gibco, Waltham, MA) was added and the cells were further cultured for 2 h. After washing with PBS (0.01 M, pH 7.4) for a total of three times, the cells were analyzed by fluorescence microscope and microplate system. The relative fluorescence intensity (RFU) was used to indicate the uptake of MIC-NPs by these cells. RFU = fluorescence intensity in experimental group/fluorescence intensity in control group.

M2 cells were seeded in six-well plates at a density of 10⁶ cells per well for 24 h. One microliter of mannose was added in the experimental group; 3 h later, FITC-loaded MIC-NPs were added in the experimental group, and unloaded MIC-NPs were added in the control group. The incubation method is the same as above. The cells were analyzed by fluorescence microscope and microplate system.