Fig 2: mGluR2 is important for SARS-CoV-2 infection of mice.a Multiplex immunofluorescence staining for the detection of mGluR2-positive cells in olfactory epithelium sections of young mouse infected with SARS-CoV-2 on day 3 p.i.. SARS-CoV-2 N protein (red), mGluR2 (green), Ace2 (magenta), GAP43 (white), CK5 (gold), CK8 (yellow), and OMP (cyan). The yellow and green areas are shown adjacently at a higher magnification, respectively. The dashed box indicates the individual cell boundary. b Multiplex immunofluorescence staining for the detection of mGluR2-positive cells in lung sections of young mouse infected with SARS-CoV-2 on day 3 p.i.. SARS-CoV-2 N protein (red), mGluR2 (green), Ace2 (magenta), Foxj1 (white), SPC (gold), Tubb4 (yellow), and CC10 (cyan). The yellow and green areas are shown adjacently at a higher magnification, respectively. The red arrows indicate a mGluR2+/SARS-CoV-2+/Ace2+/CC10+ cell, and the green arrows indicate a mGluR2+/SARS-CoV-2+/Ace2+ cell. c The 3D-rendered image was generated by using Imaris software and the co-localization of mGluR2 and SARS-CoV-2 from the two single fluorescence channels is showed. d–g mGluR2 gene knockout (mGluR2-/-) (n = 13) and WT (n = 12) mice were infected with HRB26M (150 PFU/mouse), a mouse-adapted SARS-CoV-2 strain, via intranasal inoculation. At 3 days p.i., viral RNA copies and virus titers in the nasal turbinates (d, e) and lungs (f, g) were determined by use of qPCR (d, f) and plaque assays (e, g), respectively. The horizontal dashed line indicates the limit of detection. Data represent the sum of three independent experiments (d–g), means ± SD, Student’s t-test, ***P < 0.001.