SARS-CoV-2 Omicron variant causes brain infection with lymphoid depletion in a mouse COVID-19 model

• Published in: Laboratory animal research Vol. 39; no. 1; p. 8
• Main Authors: Lee, Na Yun, Lee, Youn Woo, Hong, Seung-Min, On, Dain, Yoon, Gyeong Min, An, See-He, Nam, Ki Taek, Seo, Jun-Young, Shin, Jeon-Soo, Choi, Yang-Kyu, Oh, Seung Hyun, Yun, Jun-Won, Lee, Ho Young, Choi, Kang-Seuk, Seong, Je Kyung, Park, Jun Won
• Format: Journal Article
• Language: English
• Published: England BioMed Central 09.05.2023; BMC; 한국실험동물학회
• Subjects: Animal model; Animal models; Antibodies; Antigens; Apoptosis; Body temperature; Body weight; Body weight loss; COVID-19; Encephalopathy; Hybridization; Infections; Inflammation; K18-hACE2; Laboratory animals; Lungs; Lymphoid depletion; Nucleocapsids; Severe acute respiratory syndrome coronavirus 2; Short Communication; Transgenic animals; Viruses; Wuhan; 수의학; United States > US; China; Animal model; K18-hACE2; Lymphoid depletion; Wuhan
• ISSN: 1738-6055; 2233-7660; 2233-7660
• DOI: 10.1186/s42826-023-00157-4

The Omicron variant has become the most prevalent SARS-CoV-2 variant. Omicron is known to induce milder lesions compared to the original Wuhan strain. Fatal infection of the Wuhan strain into the brain has been well documented in COVID-19 mouse models and human COVID-19 cases, but apparent infections into the brain by Omicron have not been reported in human adult cases or animal models. In this study, we investigated whether Omicron could spread to the brain using K18-hACE2 mice susceptible to SARS-CoV-2 infection. K18-hACE2 mice were intranasally infected with 1 × 10 PFU of the original Wuhan strain and the Omicron variant of SARS-CoV-2. A follow-up was conducted 7 days post infection. All Wuhan-infected mice showed > 20% body weight loss, defined as the lethal condition, whereas two out of five Omicron-infected mice (40%) lost > 20% body weight. Histopathological analysis based on H&E staining revealed inflammatory responses in the brains of these two Omicron-infected mice. Immunostaining analysis of viral nucleocapsid protein revealed severe infection of neuron cells in the brains of these two Omicron-infected mice. Lymphoid depletion and apoptosis were observed in the spleen of Omicron-infected mice with brain infection. Lethal conditions, such as severe body weight loss and encephalopathy, can occur in Omicron-infected K18-hACE2 mice. Our study reports, for the first time, that Omicron can induce brain infection with lymphoid depletion in the mouse COVID-19 model.