Suppression of antibacterial immunity by infection with influenza virus.

The effect of influenza virus infection on systemic antibacterial resistance was assessed in a mouse model. Prior infection with influenza virus by the intranasal route led to a reduced level of macrophage activation in response to intravenous challenge with Listeria monocytogenes. Specific immunity to Listeria was measured using adoptive transfer of immune spleen cells. Preinfection of recipient mice with influenza virus reduced the level of adoptive immunity. Influenza virus preinfection of immune cell donors produced a similar decrease, which suggested that specific thymus-derived cell-mediated immunity was impaired in addition to macrophage function. The exact mechanism affected by influenza virus infection was not clear, but there was thought to be a direct effect on the macrophage with a secondary effect on the thymus-derived cell via its accessory role in the specific immune response. The immune parameters studied were still depressed at a time when actual resistance was enhanced, a result which implied that nonimmunologic factors may be involved in the enhanced susceptibility to secondary infection.