Although considered an autoimmune disease, the mechanisms underlying oligodendrocyte (OL)/myelin injury in multiple sclerosis (MS) remain to be established. We utilized in vitro assays to demonstrate that human OLs, as well as other glial elements (astrocytes, microglia), were susceptible to injury mediated by peripheral blood-derived mononuclear cell preparations (MNCs) enriched for natural killer (NK cells) by depleting CD3(+) +/- CD19(+) cells through use of either magnetic beads or cell sorting. Cytotoxic effects of the NK cell-enriched effectors were dependent on pre-exposure of these cells to IL-2. Furthermore, we found that autologous OLs were as susceptible to injury mediated by IL-2 activated NK cells as were heterologous OLs. In context of the tissue injury that occurs in MS, our results suggest that the inflammatory milieu in MS lesions could provide conditions required for NK cell activation and that such effector cells can bypass the putative protective effects of self-MHC class I molecules that may be expressed on OLs.