Fig. 2: Neuronal pathology and cell death in SARS-CoV-2 infection.

Representative H&E images show a healthy Purkinje cell layer in the cerebellum of a non-infected control RM6 (a) and reveal cell death-associated neuronal changes in cerebellum of infected animals, (AGM4 b, AGM3 c), and brainstem from AGM3 (d). Arrows indicate pyknotic and karyolitic Purkinje cells and cellular blebs. Asterisks denote areas of tissue necrosis/vacuolation on H&E sections (b) and (d). H&E was performed and assessed twice on all brain regions. Neuronal degeneration in cerebellum was only seen in the context of infection, visualized by positive, green FluoroJade C-stained neurons (AGM2 e, AGM1 f). FluoroJade C staining was performed twice on the brain regions investigated. Abnormal neuronal morphology and cleaved caspase 3 positivity is demonstrated in cerebellum (AGM3 g) and brainstem (RM2 h). Summary data of cleaved caspase 3 positive cells stratified by brain region (i) where n = 4 biologically independent samples/brain region in the control group and n = 8 biologically independent samples/brain region in the infected group, except OL where n = 7 infected animals. Immunohistochemical staining for cleaved caspase 3 was performed twice on all brain regions. Statistics were performed with a two-tailed Mann–Whitney U test. *p ≤ 0.05 and **p ≤ 0.005 comparing mock-infected to infected animals. Data are expressed as mean ± SEM. p values: CER = 0.0081, BS = 0.0182, FL = 0.0323, OL = 0.0061, TL = 0.0485, PL = 0.0485, BG = 0.0040 (control vs. infected). Source data are provided as a Source Data file. Abbreviations: CER cerebellum, BS brainstem, FL frontal lobe, OL occipital lobe, TL temporal lobe, PL parietal lobe, BG basal ganglia, C control, I infected, AGM African green monkey, RM Rhesus macaque. Scale bars = 100 µm (a, c–f, h) and 50 µm (b, g).