A study is presented which investigated whether oral immunization with a polyvalent bacterial lysate (
Paspat oral) can sufficiently enhance cell-mediated defense mechanisms to protect mice against influenza A virus
infection. It was found that oral immunization reduced mortality due to
influenza A
infection with 15-70%, depending on the quantity of virus administered and and the moment of
infection.
Cyclosporin A severely reduced the protective effect of oral immunization, suggesting that a major effect of oral immunization in these studies is T-cell activation. The effect of oral immunization on macrophageal activity was evaluated by measuring
cyclic-AMP in alveolar macrophages (AMs) obtained by bronchoalveolar lavage. Before
infection, basal activity levels of AMs in immunized mice were significantly lower than in controls. Five days after
infection, however, basal activity level of AMs in immunized mice was significantly higher than AM activity in controls. Stimulation of AMs with
PGE2 significantly reduced cellular activity in both groups, before and after
infection. However, cellular activity of AMs from immunized animals was less reduced than cellular activity of control macrophages. Activity of AMs of immunized animals was significantly more reduced by
histamine than activity of control macrophages. It is concluded that oral immunization with
Paspat oral stimulates T-cell-dependent immune mechanisms, resulting in protection against influenza A virus
infection in mice.