As one of the most devastating kinds of chronic pain, neuropathic pain, defined as pain caused by a lesion or disease of the somatosensory system [1], is a great challenge to physicians [2]. Decades of investigation using pre-clinical models has provided ample evidence of the contribution of the adaptive immune system (lymphocyte-mediated immune responses), to the development of neuropathic pain [3]. Specifically, using a well-established murine model, spinal nerve L5 transection (L5Tx), our laboratory has demonstrated that spinal cord-infiltrating CD4+ T lymphocytes contribute to the maintenance of L5Tx-induced mechanical hypersensitivity [4], indicating the involvement of helper CD4+ T lymphocyte-mediated immune responses in neuropathic pain. It is well known that helper CD4+ T lymphocytes can be classified into several functional subtypes, including type 1 (Th1, mediating primarily cell-mediated immunity), type 2 (Th2, mediating primarily humoral responses), and type 17 (Th17, mediating primarily inflammatory responses) helper T cells [5]. Each subtype of helper T cells has a distinct transcription factor and cytokine profile that drives the downstream responses they mediate. Previously, a limited number of studies that used indirect approaches suggested that Th1 is the dominant helper T cell subtype in mediating the development of neuropathic pain. First, Moalem et al. demonstrated that the passive transfer of in vitro maintained Th1, but not Th2, cells promoted nerve injury-induced behavioral hypersensitivity [6]. Others have subsequently shown the close association between increased spinal cord interferon IFN-γ (the signature cytokine produced by Th1 cells) and behavioral hypersensitivity, as well as an association between increased interleukin (IL)-4 (the signature cytokine produced by Th2 cells) expression and a reduction in nerve injury-induced sensory hypersensitivity [7,8]. More recently, the involvement of IL-17 (the signature cytokine produced by Th17 cells) in the development of peripheral nerve injury-induced neuropathic pain was described, suggesting a role of Th17 in neuropathic pain [9–11]. However, there have been no studies that directly examined the phenotype(s) of the infiltrating CD4+ T lymphocytes following peripheral nerve injury, which may in part be due to the technical difficulty of isolating the small number of lumbar spinal cord-infiltrating T cells. Thus, in the current study, we directly evaluated spinal cord-infiltrating CD4+ T lymphocytes based on their intracellular expression profiles of subtype-specific transcription factors and cytokines via flow cytometric analysis using the L5Tx model of neuropathic pain. As we did not detect significant changes in IL-17 expression in the lumbar spinal cord post-L5Tx in preliminary studies, we focused our investigation on the Th1 and Th2 subtypes.