Conclusions
It seems that noise exposure can activate a cochlear immune response, which in the presence of Ag, allows for greater recruitment of inflammatory cells than occurred in response to Ag alone.
Methods
We sensitized mice to an Ag, injected it intrathecally, and subsequently exposed the mice to noise (8-16 kHz, 90, 100, or 118 dB for 2 hours). Control mice received either noise exposure alone (100 or 118 dB), Ag challenge alone, intrathecal surgery and phosphate-buffered saline injection or no treatment. Four hours or 7 days later the mice were killed and cochlear sections were evaluated immunohistochemically for CD45, ICAM-1, and phospho-nuclear transcription factor-kappaB expression.
Results
Intrathecal Ag injection caused no hearing loss, but did result in a small immune response. Loud noise (118 dB) caused severe hearing loss and slight inflammation. The number of CD45-positive cells was significantly greater in the Ag plus-118 dB noise group relative to the Ag-alone group or 118 dB noise-exposure group. ICAM expression was seen in the lower part of the spiral ligament and small vessels within the normal cochlea. The amount of expression increased after Ag injection and acoustic trauma. Activated nuclear transcription factor-kappaB occurred in the nuclei of hair cells, supporting cells, spiral ligament fibrocytes, and neurons 4 hours after noise exposure. Conclusions: It seems that noise exposure can activate a cochlear immune response, which in the presence of Ag, allows for greater recruitment of inflammatory cells than occurred in response to Ag alone.