The IL-7R alpha single nucleotide polymorphism rs6897932 is associated with an increased risk for multiple sclerosis (MS). IL-7Ra is a promising candidate to be involved in autoimmunity, because it regulates T cell homeostasis, proliferation, and antiapoptotic signaling. However, the exact underlying mechanisms in the pathogenesis of MS are poorly understood. We investigated whether CD4 and CD8 lymphocyte subsets differed in IL-7R alpha expression and functionality in 78 MS patients compared with 59 healthy controls (HC). A significantly higher frequency of IL-7R alpha(+) CD8 effector memory (CD8EM) was found in MS. Moreover, IL-7R alpha membrane expression was significantly increased in MS in naive and memory CD8 (all p<0.05) with a similar trend in CD8EM (p=0.055). No correlation was found between the expression level or frequency of IL-7R alpha(+)CD8(+) and rs6897932 risk allele carriership. Upon IL-7 stimulation, MS patients had stronger STAT5 activation in CD8EM compared with HC. IL-7 stimulation had a differential effect on both mRNA and protein expression of granzyme A and granzyme B between MS and HC. Stainings of different lesions in postmortem MS brain material showed expression of IL-7 and CD8(+)IL-7R alpha(+) in preactive, but not in active, demyelinating MS lesions, indicating involvement of IL-7R alpha(+) lymphocytes in lesion development. The intralesional production of IL-7 in combination with the lower threshold for IL-7 induced cytotoxicity in MS may enhance the pathogenicity of these CD8 T cells. This is of special interest in light of the established demyelinating and cytotoxic actions of granzyme A. The Journal of Immunology, 2012, 188: 1874-1883.