Abstract

Feline calicivirus (FCV) is a primary cause of upper respiratory tract infections and oral ulcerative disease in cats and exhibits substantial genetic diversity that complicates prevention and control. In this study, we isolated the FCV‐BJ616 strain, established a reverse‐genetics system, and investigated its pathogenic mechanisms, thereby providing a foundation for antibody‐based therapies and broad‐spectrum vaccine development. The virus was purified by three rounds of plaque cloning, and its morphology was examined by electron microscopy. VP1 expression was confirmed by immunofluorescence and Western blotting. Using integrated systems‐biology and reverse‐genetics approaches, an infectious clone of rFCV‐BJ616 was successfully assembled and rescued, exhibiting genetic stability comparable to that of the parental strain. In vivo infection experiments showed that rFCV‐BJ616 retained wild‐type virulence, causing persistent high fever, weight loss, and multiorgan pathology in infected cats. Proteomic analysis indicated that infection with FCV‐BJ616 or rFCV‐BJ616 markedly activated cytokine‐mediated inflammatory signaling pathways. Both FCV‐BJ616 and rFCV‐BJ616 significantly upregulated the expression of IL‐8, S100A8/A9, and TLR3, which are associated with acute inflammation and tissue damage. Furthermore, elevated IFN‐β levels concomitant with STAT1 downregulation suggested a transient attenuation of antiviral signaling during early immune activation. These findings were corroborated by ELISA‐based validation of serum cytokine profiles. Collectively, this study provides new insights into the molecular pathogenesis and evolution of FCV‐BJ616 and establishes a robust reverse‐genetics platform for precise genome manipulation and future vaccine development. This study successfully isolated the FCV‐BJ616 strain derived from cats and established a reverse genetics system. In vivo experiments showed that rFCV‐BJ616 exhibits wild‐type virulence, leading to high fever, weight