In summary, our data support that lumbar spinal cord infiltrating Th1, and not Th2, CD4+ T lymphocytes mediate the maintenance of peripheral nerve injury-induced neuropathic pain. These infiltrating Th1 CD4+ T lymphocytes are likely to mediate their effects in mechanisms involving multiple Th1 cytokines and glial activation. Further investigation of CD4+ T lymphocyte-mediated pathways may result in novel, more efficacious treatments for neuropathic pain.