Intrathecal anti-IL-6 antibody and IgG attenuates peripheral nerve injury-induced mechanical allodynia in the rat: possible immune modulation in neuropathic pain.

Interleukin-6 (IL-6) is a pleiotrophic cytokine with a diverse range of actions including the modulation of the peripheral and central nervous system. We have previously shown significant IL-6 protein and messenger RNA elevation in rat spinal cord following peripheral nerve injury that results in pain behaviors suggestive of neuropathic pain. These spinal IL-6 levels correlated directly with the mechanical allodynia intensity following nerve injury. In the current study, we sought to determine whether it is possible to attenuate mechanical allodynia and/or alter spinal glial activation resulting from peripheral nerve injury by specific manipulation of IL-6 with neutralizing antibodies or by global immune modulation utilizing immunogamma-globulin (IgG). Effects of peripheral administration of normal goat IgG and intrathecal (i.t.) administration of IL-6 neutralizing antibody, normal goat or normal rat IgG on mechanical allodynia associated with L5 spinal nerve transection were compared. Spinal glial activation was assessed at day 10 post surgery by immunohistochemistry. Low dose (0.01-0.001 microg) goat anti-rat IL-6 i.t. administration (P=0.025) significantly decreased allodynia and trended towards significance at the higher dose (0.08 microg to 0.008 microg, P=0.062). Low doses (0.01-0.001 microg) i.t. normal goat and rat IgG significantly attenuated mechanical allodynia, but not at higher doses (0.08-0.008 microg; P=0.001 for both goat and rat IgG). Peripherally administered normal goat IgG (30 or 100 mg/kg) did not attenuate mechanical allodynia. Spinal glial activation was unaltered by any treatment. These data provide further evidence for the role of central IL-6 and neuroimmune modulation in the etiology of mechanical allodynia following peripheral nerve injury.