Comparative pathogenicity of vaccinia virus and mpox virus infections in CAST/EiJ mice:Exploring splenomegaly and transcriptomic profiles

Yongzhi Hou; Jianrong Ma; Baoying Huang; Na Li; Lin Zhu; Ziqing Jia; Jiasen Yang; Jingjing Zhang; Wenjie Tan; Jing Xue

doi:10.1002/ame2.70026

Abstract：Background: Vaccinia virus (VACV) and mpox virus (MPXV) belong to the ortho-poxvirus genus and share high genetic similarity, making VACV widely used in the mpox pandemic. CAST/EiJ mice have been widely used for studying orthopoxvirus infection. However, the histopathological features of CAST/EiJ mice with mpox virus (MPXV) and vaccinia virus (VACV) infections have not been fully elucidated. Methods: Four groups of CAST/EiJ mice were challenged with low-dose VACV (10^3 PFU, VACV-L), high-dose VACV (10^6 PFU, VACV-H), MPXV (10^6 PFU) or PBS via intraperitoneal route, and the disease signs and body weight were monitored daily. Subsequently, viral loads and titers in the blood and spleen of CAST/EiJ mice were analyzed via qPCR and TCID50 assay. Finally, the spleen samples were analyzed for histopathological, immunohistochemical and RNA-seq. Results: Herein, we found that VACV-L and MPXV caused splenomegaly via the intra-peritoneal route, whereas VACV-H caused rapid lethality with limited splenomegaly. Transcriptome analysis from spleen revealed significant differences in gene expression between VACV-L and VACV-H groups, but the differentially expressed genes induced by splenomegaly between VACV-L and MPXV groups were highly similar. Furthermore, pathway enrichment analysis demonstrated that the VACV-L, VACV-H, and MPXV groups were all associated with the calcium, MAPK, and PI3K-Akt signaling pathway. Compared to the lethal infection observed in VACV-H group, the splenomegaly in the VACV-L and MPXV groups was characterized by extramedullary hematopoiesis and increased macrophages infiltration in the red pulp. Transcriptome analysis of the spleen demonstrated that the Wnt, tumor necrosis factor (TNF), and transforming growth factor β (TGF-β) signaling pathways may promote splenomegaly by modulating granulocyte infiltration and inflammatory responses. Compared to VACV-L group, the limited splenomegaly but lethality in VACV-H-infected mice might be associated with extensive splenic necrosis, diffuse congestion, and hemorrhage in the red pulp, as well as changes in the cGMP-PKG, Ras signaling, and Fc gamma R-mediated phagocytosis pathways. Conclusions: Our findings systematically compared the pathogenicity of VACV and MPXV in CAST/EiJ mice, incorporating splenic transcriptome analysis to provide insights into the potential molecular mechanism behind orthopoxvirus-induced splenomegaly in CAST/EiJ mice.