Immune responses triggered by oral administration of recombinant Bacillus subtilis expressing the E2 protein of classical swine fever virus.

Classical swine fever virus (CSFV) causes an acute, febrile, and highly contagious disease of domesticated pigs and wild boars, resulting in substantial economic losses to the global swine industry. Conventional injectable vaccines fail to induce mucosal immunity and thus cannot block viral invasion via the digestive and respiratory tracts as the primary infection sites. In contrast, oral vaccines mimic the natural infection route and activate mucosal immune responses, thereby emerging as a novel direction for CSFV control. However, the degradation of vaccine antigens by the harsh gastrointestinal environment has limited development and application. Bacillus subtilis, a safe and efficient oral vaccine vector, can form spores that protect encapsulated antigens from gastrointestinal extremes, and possesses superior capabilities for heterologous protein expression and probiotic properties that improve intestinal microecology. The major structural E2 protein of CSFV effectively induces neutralizing antibody production, and its surface-specific epitopes serve as the molecular basis for targeted recognition by the host immune system. In this study, B. subtilis strain WB800N was used to construct a recombinant strain secreting the CSFV E2 protein. The mucosal immunogenicity of the recombinant strain was evaluated using a mouse oral immunization model, and its capacity to induce CSFV-specific immune responses was investigated. This research provides theoretical and experimental foundations for the development of safe and effective oral vaccines against CSFV.