Abstract
Listeria monocytogenes is an important intracellular bacterial pathogen that causes listeriosis in humans and animals, leading to severe systemic disease and posing a significant public health concern. The present study was conducted to evaluate the immunological and histopathological efficacy of a WSLAgs vaccine in an experimental rat model. Thirty adult male rats were randomly allocated into four experimental groups: negative control, positive control, vaccinated, and challenged groups. The vaccinated animals received the sonicated vaccine and were subsequently challenged with L.M. Serum levels of interferon-gamma (IFN-γ), interleukin-6 (IL-6), and immunoglobulin G (IgG) were determined using enzyme-linked immunosorbent assay (ELISA). Histopathological changes in the brain, liver, and spleen were evaluated using hematoxylin and eosin staining. On day 28 post-immunization, the WSLAgs group exhibited significantly higher serum levels of IFN-γ (173.8 ± 9.39 pg/mL) and IgG (129.9 ± 28.59 ng/mL) than the infected group (117.6 ± 15.72 pg/mL and 81.93 ± 14.73 ng/mL, respectively) (P≤0.05). In contrast, IL-6 levels were significantly lower in the vaccinated group (84.01 ± 6.32 pg/mL) compared with the infected group (427.2 ± 120.2 pg/mL) (P≤0.05), indicating attenuation of the inflammatory response. Histopathological examination revealed a marked reduction in the severity of lesions in the brain, liver, and spleen of vaccinated animals compared with the infected group, suggesting enhanced protective immunity. These findings demonstrate that the whole sonicated Listeria monocytogenes vaccine effectively stimulated both cellular and humoral immune responses while reducing tissue damage following experimental infection. Therefore, the sonicated vaccine represents a promising candidate for protection against listeriosis; however, further studies are required to evaluate its long-term protective efficacy and potential practical applications.

Key words: Listeria monocytogenes, Vaccine, Whole sonicated antigen, Immune response