Inflammation and severe demyelination in the peripheral nervous system induced by the intraneural injection of recombinant mouse interleukin-12

Inflammatory cytokines appear to be involved in damage to Schwann cells, my elin and axons, although the exact role of the different cytokines is uncer tain. The direct injection model offers a new and simplified way of examini ng the mechanisms of early inflammation in the peripheral nervous system. T he present study was performed to assess the direct effects of interleukin (IL)-12 on rat sciatic nerves injected with recombinant mouse IL-12. Histol ogical and immunohistochemical examination 24 h after injection showed earl y inflammation as well as demyelination within the injected nerve fibres. B y 4 days the inflammatory and demyelinating changes were significantly incr eased. Seven days after injection, the endoneurium still contained signific ant numbers of inflammatory cells and the demyelination was even more sever e. Control rats injected with sterile phosphate-buffered saline exhibited n o such inflammatory and demyelinating response. These changes are similar t o those seen in inflammatory and demyelinating disorders of the peripheral nervous system and suggest that IL-12 could be relevant to the pathogenesis of demyelinating diseases such as Guillain-Barre syndrome.