Immunogenicity of culture filtrated proteins and whole-cell killed formalin of Listeria monocytogenes to induced cellular immune response in vivo.

Background: Listeria monocytogenes (LM) is a life-threatening bacterium affecting many individuals worldwide, including elderly people, pregnant women, and immune-deficient patients.

Aim: Whole-cell killed formalin of LM antigens (WKLMAgs) and Listeria culture filtrated proteins (LCFPs) against challenge-attenuated LM after two booster doses (0 and 14 days) of immunization act as an antigen activating a high level of IgG3, IgM, CXCL2, and IL-1 beta.

Methods: Forty male rats were randomly assigned to four groups. The first group served as a control negative, while the second positive (+) control was inoculation orally 1 ml with virulent (1 × 10⁷ colony forming unit CFU/ml) of LM on day 28, whereas the other two groups were injected with 1-ml WKLMAgs and 1-ml LCFPs in two subcutaneously doses with day 14 intervals, with at day 28 a challenged effective dose (1 × 10⁷ CFU/ml) of virulent LM. Serum blood parameters were measured. During the 35 days, the euthanized animal histopathology studies were performed on the spleen, liver, small intestine, and brain.

Results: The current study indicated a significant difference between WKLMAgs and LCFPs for serological tests Immunoglobulin (Ig) M, chemokine (C-X-C motif) ligand 2, Ig G3, and interleukin-1 beta compared to both negative and positive controls at P < 0.001. Additionally, the WKLMAgs and LCFPs led to a decrease in the histopathological changes of organs such as (brain, spleen, liver, and intestine) compared to the positive control, which affected the organs with microgranuloma, with a pathological difference between the WKLMAgs and LCFPs compared to the negative control group.

Conclusion: Both WKLMAgs and LCFPs are capable to be as a vaccine candidate antigen for the induction of protective immunity against L. monocytogenes.