Bifidobacterium is known to stimulate the immune system, and its administration has been shown to promote the production of proinflammatory cytokines such as interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), interleukin-2 (IL-2), interleukin-12 (IL-12), and interleukin-18 (IL-18), before viral infection in murine models, suggesting a protective effect against viral infections. Here, IL18 is linked to viral infectious disease.