Influenza virus- and cytokine-immunoreactive cells in the murine olfactory and central autonomic nervous systems before and after illness onset.

Influenza virus invades the olfactory bulb (OB) and enhances cytokine mRNAs therein at the time of illness onset. Here we show that viral antigen immunoreactivity co-localized with glial markers in the OB but could not be detected in other brain areas. Interleukin 1beta- and tumor necrosis factor alpha-immunoreactivity co-localized with neuronal markers in olfactory and central autonomic systems, and the number of cytokine-immunoreactive neurons increased at the time of illness onset [15 h post-inoculation (PI)] but not before (10 h PI). These results suggest that the OB virus influences the brain cytokines and therefore the onset of illness.