Novel coronavirus-like particles targeting cells lining the respiratory tract
LLC-Mk2 cells were transduced with (M + E) + S VLPs with (a) or without (b) PMA pre-treatment, immunostained and analyzed by confocal microscopy (Z-stacks). Rectangles indicate areas of xz plane seen in orthogonal views. ACE2 molecule was additionally stained in PMA-treated (c) or untreated LLC-Mk2 cells (d). Actin fibers are shown in red, nuclei are shown in blue, M protein is detected with anti-M antibody and visualized in green whereas ACE2 receptor is detected with anti-ACE2 antibody and visualized in yellow. Each image is a single confocal plane (xy) with its orthogonal view (xz) created by maximum projection of axial planes (thickness 3 μm). Scale bar: 10 μm. Number of VLPs internalized to LLC-Mk2 cells and the ACE2 relative quantity per cell after PMA treatment or mock-treatment was determined and is presented in graph: * P < 0.05; ** P < 0.01 (e).