*2.6. Viability of Human Monocyte-Derived Dendritic Cells (moDCs)*

The effect of functionalized SiNPs on the cytotoxicity of moDCs was assessed by the commonly used lactate dehydrogenase (LDH) assay, which determines the release of the cytoplasmic enzyme LDH. For analysis, 90 µL of LDH buffer (200 mM NaCl, 80 mM Tris/HCl, pH 7.2) was mixed with 90 µL of the media samples of moDCs stimulated for 24 h. Then, 180 µL of the LDH reaction mixture (0.4 mM NADH and 4 mM sodium pyruvate in LDH buffer) were added and the absorption at 340 nm was immediately recorded and followed over a timeframe of 15 min. Cell viability was calculated by comparing extracellular LDH activities of samples with extracellular LDH activities of moDCs treated with 0.1% Triton X-100 (total LDH release).

Additionally, the viability was determined using the Fixable Viability Dye eFluor506 (eBioscience, Waltham, MA, USA) by flow cytometric analysis using a 510/50 band pass filter. The percentage of viable cells was calculated by gating CD1a on the x-axis, indicating the well-differentiated moDCs and viability stain on the y-axis.
